CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
THE CONDITIONED TASTE AVERSION: A MEANS OF PROTECTING
l\
AERIAL
COH~1UNICATION
CABLE FROM
DAHAGE BY THE FOX SQUIRREL (,?ciurus niger)
A thesis submitted in partial satisfaction
of the requirements for the degree of Master of Science in
Biology
by
David Lava.un Watkins
----
August, 1979
The thesis of David Lavaun \vatkins is approved:
---~-­
Jim VJ
Jtoh~
01
Dole
R. S\vanson
George F": Fisler, Corruni ttee Chairman
California State University, Northridge
August, 1979
ii
ACKNOWLEDGHENTS
T wish to thank all of the fine people at Pacific
Telephone Company who provided me with the technical
assistance needed to make this study possible, especially
Lee Nelson, Clyde Nelson, Leonard Morrow, Charles Weller,
Ken Brock, Bob Rollo and Don Trigg.
A special debt of
gratitude is owed to Dick Speidel and the University
Relations Committee for making the field study possible.
A special thanks goes to Lincoln \vard, general manager of
Pacific Telephone, for providing materials and equipment
needed for the field study.
In addition, I wish to thank Terry Liggett for the
fine photographs of the squirrel damage used in this paper.
I
wish to thank Professor Andrew Starrett for his help and
advice and Hary Jane Teiman for her suggestions on foods
used in experiment three.
I wish to thank the members of my committee, Dr.
George Fisler, Dr. Jim Dole and Dr. John Swanson for their
assistance and advice during the course of this study.
Finally~
I
want to thank my wife Judy, my son
Michael, and my daughter Dana for their help in the care
and feeding of the fox squirrels.
iii
TABLE OF CONTENfS
ACKNO\vL:CDGMENTS
LIST OF TABLES
LIST OF. FIGURES .
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
Field Experiment
Site Selection Method
Sampling Units
Experimental Site Descriptions
Data Collection Method
Alterations In Study Sites
Laboratory Experiments
Experimental Procedure
Experiment I
Experimerrt I I
Experiment III
Control Animals
RESULTS
Field Experiment
Data Analysis
Statistical Analysis
Laboratory Experiments
Experiment I
Experiment II
Experiment III
DISCUSSION AND CONCLUSIONS
LITERATURE CITED
iv
iii
v
vii
ix
1
6
6
6
11
12
37
lt-3
46
47
50
52
55
57
58
58
53
66
70
70
78
81+
91
106
TABLES
Table
1.
2.
3.
4.
5.
6.
7.
8.
9.
Page
Damage repairs, for each geographic area, during
the tenth (and final) rainstorm of December,
1977, and the first, second and third rainstorms
of January, 1978.
7
Squirrel damage repairs made by Pacific Telephone
Company employees from January, 1976 through May,
1978, in the Cedros and Reseda areas. The
squirrel damage is discovered when rainwater or
other moisture enters the cable through ·the
damaged insulation. Therefore, the damage may
not have occurred during the month in which it
was repaired .
9
The distribution of damage repairs made over the
time period used for site selection. (T)-Test
Site; (C)-Control Site.
10
The values computed for a lethal dose of lithium
chloride for each fox squirrel, based on
individual body weight and a given value for Mus
of 1.06 grams per kilogram of body wei~ht when
given as an intraperitoneal injection \J.T.
Baker Chernical Co.~ 1978).
49
Attacks and damage sustained by sampling units
from April 27, 1978 through June 13, 1978.
59
Attacks and damage sustained by sampling units
from June JJ+ s 1978 through July 13, 1978.
60
Attacks and damage sustained by sampling units
from July 14, 1978 through September 21, 1978.
61
Attacks and damage sustained by sampling units
from September22e 1978 through November 21,
1978.
63
A summary of the attacks and damage sustained by
sampling units from April 27, 1978 through
November 21, 1978.
64
10. A comparison of the number of attacks and the
damage sustained by test and control sites.
v
65
Table
Page
11. Percent LD 50 of LiCl Consumed/Percent of Test
Food Consumed for laboratory experiment number
one.
72
12. Test food consumption for experiment number
three,
86
vi
FIGURES
Page
Figure
1.
2.
3.
4.
5.
6.
7.
8.
9.
A schematic drawing of the Costella-Colbath
site (Test Site 1).
16
A schematic drawing of the Murietta-Costello
site (Test Site 2).
20
A schematic drawing of the Andasol Avenue site
(Test Site 3).
25
A schematic drawing of the Columbus Avenue site
(Control Site 1).
28
A schematic drawing of the Nestle Avenue site
(Control Sit:e 2).
32
A schematic d:cawing of the Corbin-Redwing site
(Control Site 3).
36
A section of lead-coated cable shmving the
beginning of a hole in the outer insulation
caused by squirrels gnawing on the cable.
38
A hole gnmved in a splice case (an old repair)
Here, s orne of ·the t e>oth marks run para lle 1 with
the long axis of the cable, due to the rounded
nature of the end of the splice case, where the
squirrel is able to apply pressure in all
directions.
39
A hole gnawed in the center of a length of leadcoated cable. Notice that the tooth marks are
primarily across the diameter of the cable. The
present opening is being enlarged at the edges
of the hole.
40
10. The feeding behavior of six fox squirrels
(Sciuru~ niger), at the three different levels
of toxicity, l,vhich were tested in experiment
number one. The squirrels did not receive any
test food on days 7 and 10 and the gaps in the
figure are to so indicate.
74
11. The percentage of an LD 50 for lithium chloride
consumed by the test squlrrels during the three
separate tests of experiment number one.
vii
76
Figure
Page
12. The feeding behavior of eight fox squirrels
(Sciurus niger) at the toxicity level of
LiCl tested in experiment pumber three.
88
13. The percentage of an Ln 50 for LiCl consumed
by the test squirrels during experiment number
three.
90
viii
':">-
.
ABSTRACT
THE CONDITIONED TASTE AVERSION: A HEANS OF PROTECTING
AERIAL COHMUNICATION CABLE FROM
DAMAGE BY THE FOX SQUIRREL (Sciurus niger)
by
David Lavaun Watkins
Master of Sctence in Biology
August, 1979
Laborato:cy experiments demonstrated that lithium
chloride is effective in inducing a conditioned taste
aversion in the fox squirrel (§,gj,.urus niger).
Foods
treated with lithium chloride produced illness in fox
squirrels ¥Thich resulted in avoidance behavior toward those
specific foods.
Squirrels ingesting between 0.12 and 0.17
grams of lithium chloride were shown to be conditioned in
one lithium trial.
In the field, incorporation of lithium
chloride into a protective sheath placed around aerial
cable is also effective.
Three test sites, each consisting
of five test sheaths (containing lithium chloride) ten feet
in length and five control sheaths (without lithium
ix
chloride) ten feet in length, were compared to three
control sites, each consisting of ten control lengths ten
feet in length.
The amount of cable damage to the control
lengths compared to the amount of damage to the test and
control sheaths showed a significant difference in damage
sustained by the cable due to squirrel gnawing of cable
insulation.
X
INTRODUCTION
Rodents cost utility companies millions of dollars
annually due to their habit of gnawing on communication
cable.
The pocket gopher (genus Thomomys) is responsible
for the majority of damage to underground cable.
Tree
squirrels (genus Sciurus) are responsible for the majority
of damage to aerial cable.
In southern California, the
fox squirrel (Sciurus
ni.~er)
aerial cable damage.
Damage to the cable occurs when
is the primary contributor to
rainwater or other moisture enters the cable through holes
gnmved. in the protective outer insulation (Pacific
Telephone Co., pers. comm.).
Fox squirrels prevent their evergrmving incisor teeth
from overgrmving by chewing on objects which are tough in
composition.
In discussing paptive squirrels, Crandall
(1964:213) stated:
"Nest boxes, logs, and branches will usually have
to be replaced at intervals because of damage by
chewing. This is a necessary evil for not even
the hardest nuts \vill always provide the constant
attrition required to keep the animals' teeth
from overgrowing."
In the v;ri ld, gnawing of objects by squirrels :i_s also a
'necessary evil', for overgrown incisors can result in
death.
Fox squirrels living in urban or suburban areas
utilize telephone cable as a relatively safe means of
traveling throughout their home range.
1
They can cross
2
busy streets in rush hour t.raffic without the slightest
danger.
By remaining arboreal, the fox squirre1 avoids
domestic cats and dogs, its major predators in heavily
populated areas.
The use by the squirrels of telephone
cable ultimately leads to cable damage as the animals will
chew on practically anything which will wear incisor teeth.
The telephone companies (under the Bell System) have
tried numerous methods of controlling rodent damage to
their aerial cable, including poisoning, shoot:ing, electric
shock, repellents and various types of protective shields
(Pacific Telephone Co. , pers. comm.) •
In recent years,
due in part to public outcry, all but the repellents and
protective shields have been abandoned.
Repellents have
proven unreliable at best and it is the present feeling of
Bell Telephone that physical protection is the most
practical solution Ovestern Electric, pers. comm.).
However, physical protection ha.s only a limited ability to
protect aerial cable as evidenced by the continued damage
in protected areas.
Gaps in the shielding created by poor
fit and weathering allow the rodents plenty of access to
cable insulation.
Lithium chloride is a chemical capable of causing
nausea, vomiting and diarrhea in mammals ingesting it
(Goodman and Gilman, 1965).
At extreme levels of lithium
intoxication, particularly when sodium intake is low,
nervous tremor, ataxia, convulsions, coma and even death
3
can occur (Goodman and Gilman, 1965).
The emetic nature of
lithium chloride will normally prevent the ingestion and
retention of a lethal dose in animals capable of vomiting.
The toxic effect of the lithium ion is apparently due to
its temporary replacement of sodium and other monovalent
cations in various biochemical reactions (Goodman and
Gilman, 1965).
Lithium chloride has been shmvn to be an
effective conditioning agent by causing illness in animals
ingesting a food substance contaminated with the toxin.
Since the chemical is odorless and has only a slightly
saline taste (J.T. Baker Chemical Co., 1978), the illness
is associated with the taste of the food.
The association
of illness with a particular food source results in
avoidance behavior directed toward that food substance.
The use of lithium chloride to initiate avoidance
behavior, through aversive conditioning (a type of trial
and error learning) toward a. specific food substance, has
been demonstrated by several \vo:ckers.
Coyotes (Canis
latrans) have been successfully conditioned against
killing sheep (Gustavson et al., 1974; Ellins et al., 1979;
Ellins et al., 197'7); rabbits (Gustavson et al., 1976); and
turkeys (Ellins et al., 1979).
Wolves
(Canis~)
have
been successfully conditioned against killing sheep
(Gustavson et al., 1976); buteo hawks against killing mice
(Brett et al., 1976); and laboratory rats agair:si: killing
mice (Rusiniak et al.,l976a).
4
Numerous other studies of lithium aversions have
been conducted, for example, Galef and Clark, 1971, 1972;
Galef and Henderson, 1972; Wilcoxon et al., 1971; and
Rusiniak et al., 1976b.
The literature contains
innumerable studies on natural aversions, but most of this
literature comes from studies of ·mimicry, for example, J,
Brower, 1958a, 1958b, 1960; J. Brower and L. Brower, 1962;
L. Brmver, 1969; L. Brower et al., 1960; Morrell et al.,
1970; Cott, 194-0; Linsley et al., 1961.
Excellent
discussions of these aversions may be found in books by
1-Jickler ( 1968) and Grant ( 1963).
None of the literature known to me contains any
mencion of conditioning experiments on the sciurids.
The
attempts made to control rodents, such as fox squirrels,
have been related to physical protective devices or
repellentsj for example, Tigner, 1966; Jones, 1961;
Cogelia et al., 1976; Barrett et al., 1958; Pirk, 1940.
Repellents contained within cable construction for the
purpose of repelling rodents has been dealt with many
times in the past, for example, Charmoy, 1938; Buckle,
1959; Shotten, 1966; Pirk, 1940; Szilard, 1937.
For a
wealth of information on this subject see Lee (1962) and
Godwin (1976).
The medical literature is filled with studies on the
lithium ion in the body of rats and man, for example,
Smith, 1976; Altamura et al., 1975; Edelson et al., 1975;
5
Mukherjee et al., 1976; Dolman and Edmonds, 1976a, l976b.
Lithium compounds and their pharmacology have been studied
extensively and much information may be found in the
following publications, Lewis, 1977; Christensen, 1976;
The Merck Hanual, 1977; The Merck Index, 1976; Luckey et
al., 1977.
In this study, laboratory experiments were conducted
to demonstrate that lithium chloride can initiate
avoidance behavior in the fox squirrel toward a specific
food substance.
Tl1ese experiments were designed to show
approximate· amoui1ts of lithium chlor-ide required to cause
illness in the fox squirrel and the number of exposures
necessary for the erection of an effective feeding barrier
against a particular food source.
In addit.ion, a field experiment was conducted to
determine \'-7hether the incorporation of a layer of lithium
chloride into the outer insulation of an aerial cable
would serve to reduce dam.ae;e by the fox squirrel to that
cable.
6
MATERIALS AND METHODS
Field Experiment
This experiment was conducted from April 27, 1978
through November 21, 1978, in the cities of Woodland Hills,
Tarzana, Reseda and Van Nuys, in the San Fernando Valley,
Los Angeles County, California.
Site Selection t-1ethod- Pacific Telephone Company has
approximately 3200 kilometers (2000 miles) of aerial caule
in the San Fernando Valley (Pacific Telephone Co., pers.
comm.).
The company divides the area they control
(General Telephone controls one-half of the San Fernando
Valley) into six geographic areas (Table 1).
A record of
darnage to aerial and underground cable is maintained at
the:i.r maintenance headquarters in Van Nuys, California.
The type of damage, address where the damage occurred,
repair made, cause of the damage and the person repairing
the damage are recorded onto computer data cards.
These
cards are filed according to month, year and geographic
area in which the damage occurred.
In addition, a record
was maintained (for this study) of all squirrel damage to
aerial cable repaired during the tenth (and final)
rainstorm of December, 1977, and the first, second and
third rainstorms of January, 1978.
From this information
(Table 1) the Cedros and Reseda areas were chosen for
analysis.
The computer data cards from January, 1977 through
7
TABLE 1.
Damage repairs, for each geographic area, during
the tenth (and final) rainstorm of December,
1977 and the first, second and third rainstorms
of January, 1978.
10
1977
STORM NUMBER
1
3
2
Total
1978
1978
1978
8
0
1
1
10
RESEDA
16
4
1
1
2l~
CEDROS
18
2
6
2
28
Y..ESTER
7
2
2
~~
15
17
1
2
1
21
2
2
0
0
4
GEOGRAPHIC
AREA
CANOGA PARK
HAGNOLIA
LANKERSHIM
8
January, 1978, for the Cedros and Reseda areas were sorted,
separating squirrel damage from all other types of repair
(Table 2).
Addresses where the damage occurred, were
mapped to reveal concentrations of damage.
These data,
coupled with field observations and with the following
criteria in mind, were used to select the exact locations
for the study.
1.
Type of cable (lead or plastic coated).
2.
Cable location (street lead or rear yard).
3.
Method of cable support (method of attachment
to a supporting steel strand).
4.
The distribution of squirrel damage over time.
5.
Number of damage points per hundred (city)
block.
6.
Presence of fox squirrels in the area.
7.
Cable accessibility (height a.bove the grourJd).
8.
Distance or geographic barriers (for squ:h:-rels)
between sites.
9.
10.
Habitat of the site.
Amount of vegetation overhanging the cable.
The results of my analysis revealed six sites
suitable for my study.
Each location was equal to a city
(hundred) block in length.
Each site had ten, plus or
minus one, damage repairs per hundred block (Table 3).
The distribution of damage over time was equal for each
site during the ·time period selected for analysis.
The
9
TABLE 2.
Squirrel damage repairs made by Pacific
Telephone Company employees from January, 1976
through Hay, 1978, in the Cedros and Reseda
areas. The squirrel damage is discovered \vhen
rainwater or other moisture enters the cable
through the damaged insulation. Therefore, the
damage may not have occurred during the month in
which it was repaired.
1976
MONTH
J
F
M
A
M
J
J
A
s
0
N
D
CEDROS
1
91
14
13
3
7
4
1
41
5
7
13
RESEDA
7
66
11
6
18
3
3
31
14
2
2
32
AREA
1977
MONTH
J
F
M
A
M
J
J
A
s
0
N
D
CEDROS
25
4
8
2
30
5
6
34
23
1
6
46
RESEDA
10
39
3
3
7
4
1
23
16
14
8
25
J
A
s
0
N
D
ARKA
1978
MONTH
J
F
M
A
CEDROS
30
29
2
17
2
RESEDA
25
11
14
2
1
M
AREA
J
TABLE 3.
The distribution of damage repairs made over the time period used for site
selection. (T) -Test Site; (C) -Control Site.
1977
SITE
Jan
Feb
Mar
Apr
COSTELLO-COLBATH (T)
Hay
Jun
Sep
Oct
Nov
Dec
1
2
2
2
ANDASOL AVENUE (T)
1
1
1
3
4
5
1
NESTLE AVENUE (C)
CORBIN-REDVVING (C)
Aug
2
MURIETTA-COSTELLO (T)
COLUMBUS AVENUE (C)
Jul
2
1
6
4
1
4
1978
Jan
Feb
COSTELLO-COLBATH (T)
2
2
HURIETTA-COSTELLO (T)
-·
ANDASOL AVENUE (T)
1
COLUt1BUS AVEI'mE (C)
3
SITE
Mar
May
2
;:::
1
NESTLE AVENUE (C)
CORBIN -REDIHNG (C)
Apr
1
1
1
1-'
0
11
damage repairs were monitored up to the day this experiment
began, a period of sixteen months (Table 3).
This was done
to insure an even distribution of damage from one site to
another and to keep damage information for each site
current.
The locations chosen were divided into three test
and three control sites.
Each site was geographically
isolated from every other site.
Animal population sizes were estimates based on
visual observations (Giles, 1971).
Any squirrel observed
within 100 meters (109.4 yards) of the site was considered
a part of the population.
Differences in population size,
cable type, cable location, method of cable support,
vegetation overhang and habitat were divided as evenly as
possible between test and control sites,
Sampling Units- \.Vithin each site, ten sampling units were
selected.
These sampling units consisted of 3.05 meter
(10 foot) sections of cable.
The sampling units were
selected near old damage repair sites.
The control lengths were unprotected and open to
rodent attack.
All existing squirrel damage in each
control length ,.vas marked and taped up to avoid confusion
with new attacks.
The test lengths were covered with a
plastic (polyvinyl chloride) sheath manufactured by the
Zippertubing Company of Los Angeles, California.
This
plastic is designed to zip together to form a tubular
12
protective cover and has various uses in industry.
Sampling units in the test areas were of two types.
One type was modified internally.
Packets of lithium
chloride contained in vinyl electricians tape were applied
to the inside of the sheath.
The packets of lithium
chloride were designed to protect the top and sides of the
cable around which the sheath was placed.
A second t.ype of
sheath was constructed in the same manner$ but without the
lithium chloride.
Since the cable was altered from its
original appearance in the test area, a control was
deemed necessary to test whether conditioned animals
would avoid objects with the same visual cues (Brmver,
1969).
In an effort to protect their aerial cable, Pacific
Telephone has installed protective coverings on many
cables.
This cover consists of an ABS (Acronitrile-
Butydiene-Styrene) plastic, Polyvinyl Chloride or
Polyethylene shield knm.vn as squirrel molding.
Thi.s
molding is an inverted V-shaped plastic shield which
overlaps the cable and its supporting steel strand.
\vherever squirrel molding '\vas present, sufficient lengths
were removed to allow exposure of control lengths or
installation of test and control sheaths as appropriate
for the situation.
Experimental Site Descriptions- Costello-Colbath (Test
Site 1) is a residential area, located in Van Nuys,
13
California.
This site was a housing tract built in an old
walnut (Juglans regia) orchard.
found in this- site.
Many large trees were
In addition to walnut, there were
orange (Citrus sinensis), avocado (Persea americana),
allepo pine (Pinus halepensis), apple (Malus §QQ.),
western sycamore
(Platanus~.),
ash (Fraxinus £QQ.),
white alder (Alnus rhombifolia), maple (Acer §_pQ.), olive
(Olea europaea) and silk oak (Grevillea robusta) trees.
The walnut, orange and pine trees provide a year round
food supply.
Seasonal foods include apples and avocados.
Garbage cans also provided occasional opportunities for
food gathering (Lenchner, 1976).
The squirrel population 'tvas approximately ten adult
animals 1vith seasonal increases when the young were born.
Several of ·the large:c trees contained leaf nests
(Stoddard, 1920).
These nests were easily seen after the
trees had shed their leaves in the fall.
Eight leaf nests
were obse:l:'ved in the 6500 block of Costello alone.
Two of
these nests ut.ilized the telephone cable as part of the
supporting structure, where the telephone cable passed
among the limbs of a walnut tree.
Since the fox squirrel
may build and maintain several leaf nests (Lenchner, 1976;
Moore, 1957; Hall and Kelson, 1959), this is not an
indicator of population numbers, but only provides an
indication of animal residence (Stoddard, 1920).
The Castello-Colbath site comprised portions of the
14
6600 blocks of Costello, Colbath and Murietta Avenues and
the 13900 and 14000 blocks of Kittridge Street.
Five test
and five control sheaths were installed in this and every
other test site.
Locations of the sampling units in site 1 (Figure 1).
Cable A was located in the rear yard of 6602 Colbath
Avenue.
This was a north-south running cable with a lead
exterior and was completely ·Covered with squirrel molding.
One test and one control sheath were installed in the open
on the north side of the yard.
The control sheath (2) was
installed south of and continuous with the ·test sheath (1).
Cable B was located in the rear yard of 6602 Costello
Avenue.
This was a north-south running cable \vith a
plastic (polyethylene) exterior and was completely covered
with squirrel molding.
One test sheath (9) was installed
just north of pole number 157465M.
Cable C crosses Kittridge Street midway bet\<Jeen
Costello and Murietta Avenues.
It was a north-south
running cable with a lead exterior and
covered with squirrel molding.
~Jas
completely
One control sheath (10)
was installed just south of pole number 157Lr.61M.
This
sheath overhung Kittridge Street.
Cable D is a street lead (a cable which parallels a
street, avenue, etc.), which ran in an east-west direction.
This street lead has a plastic exterior and was completely
covered with squirrel molding.
One test sheath (6) was
15
FIGURE 1.
A schematic drawing of the Costella-Colbath
site (Test Site 1).
16
L£/lEND
lobO.Z =f/OliSE
#-
----->- :::. OL l:Ji)A/'111 G[
REPAtR..
J
]
-::: C..ONIROL
.S\-lEATt-1
::; St\EATH
NLli'I\~ER
;VOrE: MAP IS NDI' TO
ANy .5C.IIt.6
17
inotalled on the western side of pole number 157465M near
the sheath on cable B.
A second test sheath (7) was
installed on the eastern side of pole number
corner of Costello and Kittridge.
157!~64-H
at the
A control sheath (8) was
added to the 'vestern side of that same pole.
Cable E was a street lead located parallel to, and
15 to 30 centimeters (6 to 12 inches) above cable D.
This
is a lead coated cable t uhich w•as covered with squirrel
molding.
One test sheath (3) was added to the cable on
the western side of pole number 157469M, adjacent to 6602
Colbath Avenue.
A control sheath (4) was installed just
west of the test sheath.
A second control sheath (5) was
installed on the eastern side of pole number 157465M,
perpendicular to the test sheath on cable B.
Murietta-Costello (test site 2) is a residential
area, located in Van Nuys, California.
similar to test site 1.
an old walnut orchard.
This site is very
It is a housing tract build in
The large trees in this area
include walnut, orange, lemon (Citrus limonia), grapefruit
(Citrus
par~),
apricot (Prunus armeniaca), red elm
(Ulmus fulva), ash, sycamore (Platanus £QQ.), avocado,
carob (Ceratoniq siliqua) and sweet gum (Liquidambar
styraciflua).
The walnut and citrus trees provide a year
round food supply.
carob.
Seasonal foods include avocado and
Garbage cans also provide some opportunity for
food gathering.
18
The squirrel population was approximately six adult
animals with seasonal increases when the young '\vere born.
Leaf nests in the larger trees indicated animals were in
residence.
Test site 2 was located 482.8 meters (528 yards)
1.
south of test site
It was separated from test site
by a small business district and a major boulevard.
1
The
fox squirrel uses telephone cable as a means of crossing
busy streets in relative safety.
However, no telephone
cable crosses this boulevard between sites 1 and 2.
The
boulevard, then, represents a formidable barrier between
the two sites.
I never observed any squirrel enter this
site from test site
1, but the close proximity of the two
sites does not eliminate that possibility.
The Murietta-Costellc site comprised portions of the
6300 blocks of Costello and Colbath Avenues and a portion
of the 6200 block of Hurietta Avenue.
Location of the sampling units in site 2 (Figure 2).
Cable F was located in the rear yard of 6303 Colbath
Avenue.
This was a north-south running cable "\vith a
plastic exterior.
This cable is what Pacific Telephone
calls a slack span, that is, a cable without a supporting
steel cable lashed to it.
One control sheath (3) was
installed in the southern side of the yard where a large
walnut tree overhung the cable.
One test sheath (4) was
installed on the north side of the yard just outside the
19
FIGURE 2.
A schematic drawing of the Murietta-Costello
site (Test Site 2).
20
--14000
VIC.TOR.Y
80ULE"VARD
L.
R.
'···::·•'
..;:;.
LEGEND
6500 -:::House NUMBE:R..
_____,..:::OLD DAMAGE
REPAIR.
[
:: TE.51 5/leATfl
[
-:.. S#EATH NUtvJJ3ER.
~
C.L;8LE H - PLASTIC
i
NOT£: fV/,4P IS NOT /0 AN'! SCALe
21
overhanging limbs of the walnut tree.
Cable G was an east-west running cable with a lead
exterior.
This cable was suspended from its supporting
steel cable by a series of \vire loops designed to prevent
squirrels from walking on the cable.
is known as inverted trapeze.
This type of cable
Cable G was primarily a
rear yard cable, but the cable passed near the cul-de-sacs
of Costello and Colbath Avenues and here may be considered
a street lead.
One control sheath (2) was installed on
cable G, 10 meters (10.9 yards) east of a small utility
pole (no number), adjacent to 6303 Colbath Avenue.
A
large walnut tree overhung the cable at this point.
A
test sheath (1) Has installed 2 meters (2.2 yards) east of
the control sheath.
This test sheath was overhung by a
large bottle brush plant
(~..?llistemon
villlinalis).
One
test sheath (5) was installed adjacent to 6302 Costello
Avenue at the western edge of the cul-de-sac.
A control
sheath (6) was i.nst.alled vlest.:. of a small pole (no number)
located at the eastern edge of the cul-de-sac.
Cable H was an east-west running cable with a
plastic exterior.
This cable crossed Murietta Avenue in
the 6200 block and passed between 6212 and 6216 Murietta.
Thls cable was covered with 12.9 meters (40 feet) of
--s-B.ea-t-h-i-n-a-e·ont-i-nuous-stretch-,-wrrere-t:tn s c c. 5Te eros sed
Murietta Avenue.
One test sheath (10) was installed to
the \vest of pole number 146 707M.
One control sheath ( 9)
22
was placed to the east of that same pole.
A test sheath
(8) was installed east of and continuous with sheath
number 9.
A second control sheath (7) was installed to
the east of and continuous with sheath number 8.
Sheaths
7 and 8 were overhung by a large ash.
Andasol Avenue (test site 3) is located in a
residential area of Resedag California.
The m.ajority of
the vegetation consisted of large (6.1 to 12.2 meter or 20
to 40 feet) coast live oaks
(Que~
line both sides of Andasol Avenue.
agrifolia), which
The canopy of these
trees completely covered the avenue in many places.
Several other species of trees \vere also found here
including olive, eucalyptus (EucalyQtus .§_QQ.), red elm,
camphox- tree (Qinnamomum camphorC!), allepo pine, Canary
Island pine (Pinus canariensi.s), orange, grapefruit,
apricot and coast redwood (Sequoia sempervirens).
The
diversity of the species in this site virtually assures
Sciurus niger a year round food supply.
cans are utilized
l-O
Again, garbage
some extent.
The squirrel pop11lation was approximately ten adult
animals, with seasonal increases when the young are born.
Leaf nests were seen in some of the large trees on the
stt~.----------------~---------------------
The Andasol site was located 6.6 kilometers (4.1
miles) due west of test site 1 and consisted of portions
of the 6500 and 6600 blocks of Andasol Avenue.
23
Locations of the sampling units in site 3 (Figure 3).
Cable I '\vas a north-south running street lead with a
lead exterior supported in the inverted trapeze manner.
This street lead ran the entire length of the 6500 and
6600 blocks, on the western side of Andasol Avenue.
One
test sheath (1) was installed at 6549 Andasol, just north
of a large coast live oak.
This sheath '\vas overhung for
fifty percent of its length by that oak tree.
A control
sheath (2) was installed at 6551 Andasol just south of
pole number 1371+27M.
One test sheath (3) was placed at
6603 Andasol just north of pole 'number 323908H.
A control
sheath (4) was ins·talled on the northern side of a pole
(no number) at 6603 Andasol.
A test sheath (5) was
installed at 6615 Andasol just south of pole number
137425M.
A second teat shea.th (6) was installed on the
north side of that same pole.
large camphor tree.
Sheath 5 was overhung by a
A control sheath ( 7) \vas placed at
6623 Andasol just south of pole number 137424M.
A second
control sheath (8) was installed to the north of that same
pole.
A test sheath (9) was installed at 6643 Andasol just
south of pole number 137423M.
A control sheath (10) was
placed to the north of that same pole.
Sheath number 10
was overhung for fifty percent of its length by a large
- - - -eea-s-t-1-i-ve--ea-k-.-----------------Columbus Avenue (Control Site 1) is located in a
residential area of Van Nuys, California.
This site was
24
FIGURE 3.
A schematic drawing of the Andasol Avenue site
(Test Site 3).
25
,..
..:;:•a
..........:•
...•:•..
..
.....
~:.
:::
...
!•
!i
b\ij
:.:t ~
·~·.
:::
;!:~
...
~
:.\'
.·:·.""'
~~· '.J
~ *?1
:~= C)
--~~~~Pole ,H.~,,
~I
~
-.....:z:o.;.-::. OLD
3Z3q OZM
V• "'\
-:·~
DAMAGE
F\EPAI R
f:~ 1.1)
~
66/JS
LEGEND
65.1Jq =A HOUSE#
[
=CoNTROL
·::
(
= TEST
~::
*"1
~.-~
:::.;z. ~
..
.......
...!::...·
·:··
•'';
...,•;......
.............
~:.:
·~t Q
~:t
::·
...~:~..
0
\()
\l)
·~·
NOT£: MAP IS NCJr TO A/Vt,l SeALE-
~11EATH
"'
.$HEATI-l
S\-\EAIH
#-
26
quite diverse in its habitat.
The majority of the large
trees at this site were coast live oak and English walnut.
Other species found here include orange, western sycamore,
olive, carob tree, silk oak, red elm, pecan (Carya
illinoensis), grapefruit and California pepper tree
(Schinus §_QQ.).
The squirrel population was approximately four adult
animals with seasonal increases when the young were born.
In addition, there is an influx of animals from surrounding
areas, when fruit is present on a large pecan tree at 6432
Columbus Avenue.
Leaf nests 1tJere found primarily on the
side streets, which run perpendicular to Columbus Avenue,
as the trees on Columbus had been heavily trimmed and most
were not suitable as nesting trees (Moore, 1957).
The Columbus site was located 2.2 kilometers (1.4
miles) due west of test site 1.
This site consisted of
portions of the 6400 and 6500 blocks of Columbus Avenue.
Locations of the sampling units in con-trol site 1 (Ftgure
4)
Cable J was a north-south running lead, with a
plastic exterior.
This street lead ran the entire length
of the 6400 and 6500 blocks on the eastern side of Columbus
Avenue.
One control length (1) was selected just south of
pole number 762509H at 6432 Columbus Avenue.
length was overhung by a large carob tree.
This control
A second
control sheath (2) was selected on the northern side of
27
FIGURE 4.
A schematic drawing of the Columbus Avenue site
(Control Site 1).
28
Lt:6f.ND
0400; l-lousE-#
----.:;.- = OLD "'DAMAGE
REPAIR.
[
:. CoNTRoL LENGTH
Pole..# 1fo25o9H
~1._/S/00
GtLMOR£
• ""l' ...... 9'' .......... ••• ••• • • • •• • • • ... •
.•;..:,..•·.
:r·:~:!······ ..-.::;.·.·~·.·: ·.:·:· . ...·.·.
'-I
~
~
..
~-
·:..·: ;·.:·.:~ ·::y
~-=·
~:-.
,.
\.
:.·
Nor£:
MAP IS No-r
-ro ANY
S~Lf"
:STREET
29
that same pole.
One control length (3) was placed at 6450
Columbus Avenue.
silk oak tree.
Control number three was overhung by a
A control length (4) was selected on the
northern side of that same tree and was overhung in a
similar manner.
One control length (5) 'vas chosen inside
the limbs of a silk oak at 6454 Columbus.
Control 6 was
located inside limbs of that same silk oak, but on the
more northern side of the tree canopy near pole number
87515M.
Control 7 was located at 6510 Columbus, just
north of pole number 762508H •. Control 7 was overhung for
fifty percent of its length by a sparsely foliated elm
tree.
Control 8 was selected at 6516 Columbus and was
overhung for fifty percent of its length by a second
sparsely foliated elm.
Control 9 was totally overhung by
a small elm tree at 6522 Cohunbus just north of pole
number 179895M.
Control 10 was located at 6552 Columbus
just north of pole number 1290151-1 and just south of a
large Chinese elm (Ulmu~ £arvifolia).
Nestle Avenue (control site 2) is located in a
residential area of Tarzana, California.
This site was
very diverse in habit.at and had many different species of
trees and shrubs.
The overall height of most of the trees
was under 6.1 meters (20 feet).
The tree species included
orange, grapefruit, alder, Canary Island pine, palm
(\vashington §_QQ.), western sycamore, olive, English walnut,
lemon, ash, jacaranda (Jacaranda acutifolia), Italian
-------------------~~-~~~~-~---
30
cypress (Cupressus
(Eucalyptus
§QQ.).
22Q.), apricot, maple and eucalyptus
The diversity of the tree species
provided an ideal habitat with a year round food supply for
the resident fox squirrels.
The squirrel population \vas approximately six adult
animals with seasonal increases when the young were born.
The only leaf nests observed were confined to the tall
eucalyptus trees near the edge of the site.
Hmvever, the
palm trees may have contained some nests which could not be
seen due to their dense foliage.
Squirrels were observed
using these trees to some extent.
The Nestle site was located 2.9 kilometers (1.8
miles) south by southwest
of the Andasol site.
This site
consisted of portions of the 5300 and 5400 blocks of
Nestle Avenue.
Locations of the sampling units in control site 2 (Figure
5).
Cable K was a nort:h-south running rear yard cable
with a lead exterior.
A control length (1) \vas selected
just north of a drop 1vire (a wire from the cable, which
connects to a residence) at 5326 Nestle Avenue.
A control
length (2) was selected at 5400 Nestle Avenue in the south
side of the yard.
Two control lengths (3 and 4) were
placed at 5406 Nestle.
Control number 3 was located in the
south side of the yard and was overhung by a large palm
tree.
Control number 4 was placed just north of control
~--~--
31
FIGURE 5.
A schematic drawing of the Nestle Avenue site
(Control Site 2).
32
t ::
(J ::'.
~
:::
'0 ••
If)::..
...·.·
.."'.......·:
....:i..
~/0
5422-
',h
.....·:··
...!,..·..
...
......,.
....
5ll18_
\...!=:G-El'{ D
5?2.6" /-lOUSE·#
----7'-=0LD
DAI'"\A&I:"
REPAIR.
#i-: CoNTRoL
LtNGIH
54oo==:
-#=
'l :·:.
<:) • :
\'I):.·
..
..
~
.I ··.:
' :...
..
...·.
-~-5331
53:Z.b-
·:
...
·~
NOT'£: MAP IS Ncrr ID
/ti'N St!.Al-1:
33
number 3 and was overhung by a second palm tree.
T\vO
control lengths (5 and 6) were selected at 5412 Nestle
Avenue.
wire.
Control number 5 was located just south of a drop
Control number 6 was located to the north of that
same drop wire.
Two control lengths (7 and 8) were chosen
at 5418 Nestle Avenue.
Control number 7 was placed in the
southern side of the yard on either side of pole number
225949.
Control number 8 was placed in the northern side
of the yard.
T\vo control lengths (9 and 10) were selected
at 5422 Nestle Avenue.
Control number 9 was placed in the
south side of the yard and \vas overhung by an Italian
cypress.
Control number 10 was placed just north of
control 9 and was also overhung by an Italian cypress.
CorbL1.-Red\ving (control site 3) \vas located in a
residential area of \\Toodland Hills, California.
was an ideal squirrel habitat:.
This site
The houses in this area had
extremely large yards which contained many frutt trees.
The area formally was composed of large citrus groves and
when houses were built, many of the trees were left
untouched by the construction.
In addition, many of the
residents have planted trees for landscaping purposes.
Tree species in this site include orange, grapefruit,
lemon, lime (Citrus aurantifolia), western sycamore, palm
silk oaki apple, apricot, sweet gum, Italian cypress,
Canary Island pine, Japanese black pine (Pinus .!Jt\lnbergjJ,
eucalyptus, olive a·nct maple.
This site contains a large
34
(30+ acre) orange and grapefruit orchard, located at the
end of the cul-de-sac of Corbin Avenue.
The squirrel population was approximately ten adult
animals, with seasonal increases when the young were born.
Leaf nests were confined to the orchard and a few large
trees on Corbin Avenue.
The Corbin-Redwing site was located 3.2 kilometers
(2.0 miles) due \vest of the Nestle Avenue site.
This site
consisted of portions of the 5400 block of Corbin Avenue
and a portion of the 19600 block of Redwing Drive.
Location of the sampling unitb in control site 3 (Figure 6).
Cable N was a north-south running rear yard cable
with a
l•~ad
exterior, which was completely covered \vith
squirrel molding.
Cable N \vas located approximately 50
meters (54.7 yards) east of Corbin Avenue.
This cable ran
in a northerly direction away from Redwi.ng Drive, toward
the 5500 block of Corbin Avenue.
w~s
One control length (10)
chosen just north of pole number 235511M, at 19637
Redwing Drive.
Cable M was an east-west running street lead with a
lead exterior, which was completely covered with squirrel
molding.
This cable was located on the northern side of
Redwing Drive in the 19600 block.
west portion of cable L.
This cable was an east-
One control leng·th ( 9) was
chosen on the western side of pole number 235511M
perpendicular to control number 10.
35
FIGURE 6.
A schematic drawing of the Corbin-Redwing site
(Control Site 3).
--------------------------~-
--------'--------
36
.....
,,='..
·:..
..
...
..
·:
.~.
-:~
..
~.
"·"""•!-,..:..
~,
....
:::;,
':s;.. \
~ ·~
"S ::·
~ :::
..::
~
'.;.:
....,
'V ..
...
~
() -~·
~ ..~:
.-:
(;)
...•,•,.~:..
.......
..:·
..
·.·....
........
.......
L.EG-END
5430= HOU.SE#
~ ~
[
r.. :.·
1it" ·:
'"I • •
•:.
..
:-.•
0
11
I
!
fi.ND oFc.A8LE
P£VA\R...
::. CoNTROL lfNG:rH
it-1
ORAN6E- &~M'E:FRu.rr CR<.\·\M<
OLtl UAMA6E
'D
r:: (.oNTR6L LENG-iH
I{UIY\'BER..
~-~-----~~-
37
Cable L was a north-south running rear yard cable
with a lead exterior, which was completely covered with
squirrel molding.
This cable ran the entire length of the
5400 block of Corbin Avenue, parallel to the rear property
lines.
Three control lengths (1, 2 and 3) were selected
in the rear yard of 5450 Corbin Avenue.
Control number 1
was located in the south end of the yard and w·as overhung
for seventy-five percent of its length by two Italian
cypress trees.
Control number two was located in the
central part of the yard.
Control number 3 was selected in
the northern end of the yard.
Three controls (4, 5 and 6)
were selected in the rear yard at 5460 Corbin Avenue.
Control number 4 was located in the south end of the yard.
Controls number 5 and 6 were located in the northern side
of the yard, with number five the more southerly of the
two.
One control length (7) was selected at 5472 Corbin
Avenue just south of pole number 235512H.
One control
length (8) was selected on the northern side of that same
pole.
Control number eight overhung Redwing Drive.
Data Collection Method - In my experience, the damage
inflicted on aerial cable by the fox squirrel is a series
of cutting motions which gradually wears away the outer
insulation, rather than puncture marks.
This is
accomplished as the animal bites across the diameter of the
cable.
Rarely are the bites parallel with the long axis of
the cable (Figures 7, 8 and 9).
This same gna\ving motion
38
\FIGURE 7.
I
:
A section of lead-coated cable showing the
beginning of a hole in the outer insulation
caused by squirrels gnawing on the cable.
Photograph by Terry Liggett
39
' FIGURE 8.
A hole gnawed in a splice case (an old repair).
Here, some of the tooth marks run parallel with
the long axis of the cable9 due to the rounded
nature of the end of the splice case, where the
squirrel is able to apply pressure in all
directions. Photograph by Terry Liggett
40
FIGURE 9.
A hole gnawed in the center of a length of
lead-coated cable. Notice that the tooth marks
are primarily across the diameter of the cable. ·
The present opening is being enlarged at the
edges of the hole. Photograph by Terry Liggett
41
is used by the squirrels to open walnut shells and other
hard coverings of foods.
Fox squirrels will return to an area which has been
damaged on a previous occasion, and proceed to lengthen the
damage point by gnawing at the edges of an existing opening
in the insulation.
After repairs have been made, the
animal may attack the repair.
Indeed, many stretches of
cable are notorious for their squirrel damage repair
records (Pacific Telephone Co., pers. comm.).
The width
of a damage point (across the cable diameter) changes very
little from one attack to another, because the size of the
cable itself is a limiting factor.
Cables are generally
damaged in the upper one third of the total circumference.
Thereafter the animal generally has some difficulty in
applying bite pressure with sufficient effec·t to damage
the cable.
This is not to say that a cable is never
damaged on its underside if the animal can maintain a
position of leverage enabling it to gnaw on the cable.
For purposes of this study variations in the width of a
damage point were not considered as a pertinent variable.
The depth of·a damage point is directly dependent on the
internal structure of the cable attacked.
A cable with a
steel liner is not penetrated as deeply as a cable without
such a liner.
Therefore, I chose to record only the
number of attacks, the length of the damage at the point of
attack (the damage point), and increases in length of a
42
previously damaged spot.
In addition, records were kept of
penetrations of the outer insulation.
Tooth marks were
recorded as attacks and were recorded as 1/8 inch (3.2 mm)
bites.
The cable was considered damaged if the outermost
insulation had been gnawed through.
Any squirrel damage
1/4 inch (6.4 mm) or longer was generally through the
outermost insulation.
Tooth punctures of the test and
control sheaths were counted as 1/8 inch bites.
The cable
was considered damaged (in test sites) if both layers of
the sheath and the outermost insulation of the cable '\vere
penetrated.
The squirrels could penetrate the soft
material of the sheath with relative ease; however, it was
hypothesized that the quick action of lithium chloride
would prevent the penetration of the outer insulation, as
the squirrel \vould become ill before this \vas accomplished.
The length of a bite in the outer insulation of the control
lengths was considered equal to the length of a bite in
the softer material of the test and control sheaths.
No
allmvance was made for differences in material density.
The installation of the test and control
sheaths~
and the marking and covering of old squirrel damage in
the control lengths, required several days to complete.
The process began on April 27, 1978 and was completed on
May 13, 1978.
The sheaths and control lengths "ivere
monitored for any signs of squirrel damage on
dates:
th·"~
follm·;ing
June 13, 1978; July 13, 1978; September ?lf 1978;
43
November 21, 1978.
The process of monitoring the sampling
units required approximately ten hours to complete and all
of the sampling units were checked on the same day.
Data were gathered with the help of one telephone
company employee.
Ladders, climbing belts and a hydraulic
lift truck (provided by Pacific Telephone Co.) equipped
with a '\vork platform \vere used.
The work pla-tform could
be raised, by means of the hydraulic lift up to the height
of the cable being monitored.
This type of truck is
commonly known as a "cherry picker".
The truck was used
to gather the data on street lead cables.
The climbing
belts and ladders were used in rear yard locations.
Damage points were measured and recorded for each test
sheath, control sheath and control length in the
appropriate site and the data for each site recorded
separately.
A Iterations In Study Sites- Several chang;es took place in
the study sites during the course of my study and the data
may have been affected as a result of these changes.
In
early May, 1978, a new cable \vas installed in ·the Andasol
Avenue test site by Pacific Telephone's construction
department.
The study was being carried out through the
maintenance department and apparently ·the construction
department was unaware of the study.
The new caL l.e was a
large diameter (3.8 em. or 1.5 in.), plastic coa·
which \vas not covered with squirrel molding.
Th
cable
cable
44
was installed parallel to cable I and was separated from
. cable I by a distance of 30.5 to 50.8 em. (12 to 20 in.).
Cable I was a small diameter (2.2 em. or 7/8 in.) cable of
the inverted trapeze type and was, therefore, difficult for
the squirrels to walk on.
The new cable was easy for the
squirrels to walk on and the squirrels were observed to
prefer it over the old cable.
During the month of May and
the first half of the month of June construction crews were
busy installing the new cable and connecting residences to
it.
The disturbance of these crews, coupled with a new
ro{lte of transportation for the squirrels, may have been
the reason for bite records for the Andasol site.
The new
cable was attacked in several places, '<vhi.ch 1.vere parallel
to the test and control sheaths on cable I, but the old
disconnected cable, which was left in place
a-i:
m.y request,
incurred no damage vJhatsoever.
In May, 1978, the majority of the orange and
grapefruit orchard within the Corbin-Red\ving site
wa.s
destroyed to make way for a tract of nmv homes.
Construction on these homes went on throughout the length
of my study with the result that the number of squirrels
observed within this site dropped to one.
The number of fox squirrels observed in the Nestle
Avenue control site dropped drastically in the month of
June, 1978; thereafter, only t"\vo squirrels were observed in
this site.
In conversing with the residents of the area,
45
I learned that a particular male house cat (Felis
domesticus) had become quite efficient at capturing and
killing fox squirrels and had reportedly killed three such
animals in recent days.
The Nestle site is extremely
isolated from other squirrel producing areas by several
large business districts to the south, east and \vest and
by the Ventura free-tvay to the north.
Immigration into such
an isolated area is either very low or nonexistant;
therefore, the loss of any individual from the population
is significant.
During the month of August, 1978, an outside
contractor to Pacific Telephone installed squirrel molding
in the Murietta-Costello test sitA and the Columbus Avenue
control site.
The squirrel molding "ivas placed over the
of the test and control sheaths in the
t~op
Hurietta.~Costello
site; control lengths were covered in the Columbus Avenue
control site.
The squirrel molding \vas removed by myself
and one telephone company employee on September 219 1978.
Since the length of time each site ·\vas covered (about 3
weeks) was approximately equal, the effects \ve:r.e considered
offsetting and were not taken into account in the data
analysis.
46
Laboratory Experiments
These experiments \vere conducted from May, 1978,
through April, 1979.
The subjects were three sub-adult
and nine adult fox squirrels (Sciurus niger).
The
squirrels were sexed by examination of the external
genitalia and aged by means of the tail characteristics
and the external genitalia (Giles, 1971) •
Six of these
animals were female (Alpha, Beta, Gamma, Delta, Epsilon,
Mu) and six were male (Zeta, Eta, Theta, Kappa, Lambda,
Iota).
Three squirrels (Epsilon, Lambda, Nu) were
sub-adults when they were captured.
All of the squirrels
were captured on or near the campus of California State
University, Northridge, California.
Six animals were
captured in the Historic Orange Grove located on the campus
and six were captured in the surrounding residential area.
The squirrels were trapped by placing live traps
baited with whole walnuts at the bases of trees which
squirrels were known to frequent.
The squirrels were maintained in a variety of cage
types and sizes ,
Alpha~
Beta., Lambda and Mu were kept in
wire mesh cages rneasuring 76 em. x 45 em. x 40 em. (29.9
in. x 17.7 in x 15.7 in.).
Gamma, Epsilon and Kappa were
kept in sheet steel and wire mesh cages measuring 60 em. x
45 ern. x 28 em. (23.6 in. x 17.7 in. x 11.0 in.).
Del~a,
Zeta, Eta, Theta and Iota were kept in wire mesh cages
measuring 60 em. x 40 em. x 35 em. (23.6 in. x 15.7 in. x
47
13.7 in.).
Each cage contained a water bottle, several
food containers and a 3.78 liter (1 gal.) glass jar for
use as a substitute nest.
The variation in cage size was
due to a shortage of uniform caging at our research
facility.
Experimental Procedure - In order to acertain the effect
of lithium chloride on fox squirrels, foods which would be
used to test them were determined by establishing a food
preference list.
The food preference was established by
offering various foods and observing both the amount of
each which was consumed and the order in which these foods
were eaten.
A va.riety of foods were offered and eliminated
until a clear order of preference was established for each
group of squirrels tested.
The types of foods offered were
based primarily on suggestions in Crandall (1964) and
observations of the animals.in the wild by myself and
descriptions in Lenchner (1976).
Foods were selected as
test foods which vtere h:tgh on the preference list and were
preferred over foods selected as safe or control foods.
Test foods \vere selected on the basis of ease of
incorporation of the lithiurrl chloride and a low
availability of these foods in the natural environment.
Since the squirrels were to be released at the conclusion
of my study, I wanted to avoid the possibility of
conditioning them against any food which was required for
their survival.
In addition, I computed an estimated
48
lethal dose-50 (an w 50 is the amount of any substance
required to kill 50 percent of the animals being tested)
of lithium chloride for each squirrel based on its
individual body weight and a previously established value
for Mus of 1.06 grams per kilogram of body weight when
given as an intraperitoneal injection (Baker, 1978; see
Table 4).
The value computed was considered low as the
chemical was to be administered orally and oral values tend
to run higher than these given by injection (Christensen,
1976).
Once the estimated lethal dose of lithium chloride
was computed and the food preference was established, one
of the more preferred foods was chosen as a poison bait
and a much less preferred food was chosen as a control.
The preferred food \vas then treated with crystaline or
powdered analytical grade (99% pure) lithium chloride and
fed to the test animals.
The control animals received
the same amount and type of food, but without the lithium
chloride.
The preferred food would then be re-offered at
a later time in an untreated condition along with a less
preferred food.
If the test animals refused to eat the
more preferred food on which they had been poisoned, but
instead ate the less preferred food and if the control
animals continued to eat these foods in their original
order of preference, it should be safe to assume that a
feeding barrier exists which is specific for the food on
49
TABLE 4.
The values computed for a lethal dose of lithium
chloride for each fox squirrel, based on
individual body weight and a given value for Mus
of 1.06 grams per kilogram of body weieht when
given as an intraperitoneal injection (J.T.
Baker Chemical Co., 1978).
COMPUTED LD 50
ANIMAL
WEIGHI
Alpha
0.540 kg. (1.19 lb.)
0.57 g.
Beta
0.660 kg. (1.46 lb.)
0.70 g.
Gamma
0.555 kg. (1.22 lb.)
0.59 g.
Delta
0.533 kg. (1.18 lb.)
0.56 g.
Epsilon
0.466 kg. (1 .03 lb.)
0 .1}9 g.
Zeta
0.548 kg. ( 1 .21 lb.)
0.58 g.
Eta
0.535 kg. ( 1 .18 lb.)
0.57 g.
Theta
0.566 kg. (1.25 lb.)
0.60 g.
Iota
0.653 kg. (1.44 lb.)
0.69 g.
Kappa
0.587 kg. (1.29 lb.)
0.62 g.
Lambda
0.474 kg. ( 1. 04 lb.)
o.so
Mu
0.469 kg. ( 1. 03 lb.)
0.50 g.
g.
50
which the animals had been poisoned.
My experiments are
not wholly original, as many of the techniques are modified
from the works of Gustavson (1974) and Galef and Clark
( 1971).
Experiment I- The subjects in this experiment were six fox
squirrels; Alpha, Beta,
Ga~~a,
Delta, Epsilon and Zeta.
Alpha and Beta were the control animals and G.9.mma, Delta,
Epsilon and Zeta were the test animals,
The food preference established for those animals
was as follows:
More preferred- walnuts
apples
filberts (hazelnuts)
oranges
peanuts
almonds
whole corn (dried)
Less preferred- rolled oats
Filberts v1ere chosen as the poison bait and a
mixture of whole corn and rolled oats served as the control
or safe food.
A twenty-four hour period \vas chosen as the
time length for each test.
The amount of lithium chloride
and its concentration (amount per individual nut) was
varied in order to establish an estimated threshold amount
of the chemical required to initiate conditioning.
On day 0 all food was removed for twenty-four hours.
51
On days 1-4 each squirrel received 8.3 grams of filberts,
30 grams of whole corn and 10 grams of rolled oats.
On
day 5 the test animals received 8.2 grams of filberts
treated \vith 0.1 gram of crystaline lithium chloride.
The
hollow center of the filberts contained the lithium
chloride.
A section was removed from each nut to allmv
the lithium salt to be added to the hollow center.
The
center was then plugged with a piece of filbert to keep
moisture mvay from the lithium chloride.
The plug \vas
also used to adjust the weight of these nuts to equal
amom1ts for each animal.
The control animals received 8.3
grams of untreated filberts which had been altered in the
same manner.
No other food was offered to avoid the
possibility of ·the animals becoming confused as to Fhich
food had made them ill.
On day 6 the results of feeding
on the poison bait "t>Jere recorded.
Any remaining treated
filberts \vere removed and each animal was given 8.3 grams
of untreated filberts, 30 grams of \vhole corn and 10 grams
of rolled oats.
On day 7 the results of the retest were
recorded and the animals were given a normal ration of
food.
On day 8 each test animal received 8.0 grams of
filberts treated \vith 0.3 gram of crystaline lithium
chloride.
The control animals received 8.3 grams of
untreated filberts.
The poison bait was prepared in the
same manner as before.
On day 9 the results of feeding on
the poison bait ·were recorded.
The remaining treated nuts
52
were removed and each animal received 8.3 grams of
untreated filberts, 30 grams of whole corn and 10 grams of
rolled oats.
recorded.
On day 10 the results of the retest were
Each animal received a normal ration of food
(walnuts, apple, orange, peanuts, whole corn and rolled
oats).
On day 11, each of the test animals were given 7.2
grams of filberts treated ·N·ith 0.3 gram of crystaline
lithium chloride.
The control animals received 7.5 grams
of untreated filberts.
On day 12, the results of feeding
on the poison bait -..-vere recorded.
The remaining treated
nuts were removed and. each animal received 7.5 grams of
filberts (untreated), 30 grams of whole corn and 10 grams
of rolled oats.
On day 13, the results of the retest were
recorded and the animals returned to normal rations.
Experiment II- Experiment number two was an attempt to
establish the number of lithium chloride treatments
necessary to initiate avoidance behavior tmvard a specific
food.
Evaluation of the da;ta from experiment one led to
the conclusion that two consecutive treatments, at a
slightly higher toxicity level than the final level
tested in experiment one, might condition the squirrels
v~ry
rapidly.
I also nmv attempted to avoid concentrating
the lithium chloride in a small area of the food.
In
addition, I hoped to slmv dovm the reaction time of the
chemical within the body of the animals and thereby allmv
more of the toxin to be ingested, through s lmv digestion
53
of the lithium-food mixture.
In order to accomplish the
above, I mixed the lithium chloride with Skippy brand,
smooth peanut butter.
The peanut butter was spread
between halved filbert nuts.
The nut halves were then
pressed back together to give the appearance of whole nuts.
The subjects in this experiment were six fox
squirrels.
Lambda and Iota were the control animals and
Beta, Eta, Theta and Kappa were the test animals.
Beta
was specially selected for this experiment, as she was the
only animal which would move freely about and feed in my
presence.
I wished to closely observe the behavior of
this animal and to record her reaction to the toxin both
durir~
and after feeding on the poison bait.
The food preference was the same as in experiment
one (see page SO).
I computed the Ln 50 for each animal,
using the same criteria as in experiment one (Table 4).
The time period selected for each test was again twentyfour hours.
chosen as
th~
Filbert nuts containing peanut butter ·were
test food.
A mixture of whole corn and
rolled oats "\vas chosen as the control or safe food.
On day 0 all food was removed for twenty-four hours.
On days 1-3 each squirrel received 6.0 grams of filberts
containing 1.0 gram of peanut butter, 30 grams of whole
corn and 10 grams of rolled oats.
On day 4 each test
animal received 6.0 grams of filberts containing 0.7 gram
of peanut butter mixed \vith 0.3 gram of lithium chloride.
54
The control animals received 6.0 grams of filberts
containing 1.0 gram of peanut butter.
On day 5 the results
of feeding on the poison bait were recorded.
The animals
were then given normal rations of walnuts, apple, orange,
peanuts, whole corn and rolled oats.
On days 6 through 9
the squirrels were also given normal rations of food.
On
day 10 the test animals received 6.0 grams of filberts
containing 0.7 grams of peanut butter mixed with 0.3 grams
of lithium chloride.
The control animals received 6.0
grams of filberts containing 1.0 grams of peanut butter.
On day J.l the results of feeding on the poison bait were
recorded and the squirrels given normal rations of food.
On day 12 the squirrels received normal rations of food.
On day 13 each animal was offered 6.0 grams of filberts
containing 1.0 grams of peanut butter, 30 grams of whole
corn and 10 grams of rolled oats.
On day 14, the results
of the retest were recorded and the animals were provided
with normal rations of food.
given a normal ration of food.
On day 15 each squirrel was
On day 16 the test animals
were offered 6.0 grams of filberts containing 0.7 grams of
peanut butter mixed with 0.3 grams of lithium chloride.
The control animals received 6.0 grams of filberts
containing 1.0 grams of peanut butter.
On day 17 the
results of feeding on the poison bait were recorded and the
squirrels were given normal rations of food.
each animal was given a normal ration of food.
On day 18,
On day 19
55
each animal received 6.0 grams of filberts containing 1.0
grams of peanut butter, 30 grams of whole corn and 10 grams
of rolled oats.
On day 20 the results of the retest were
recorded and the squirrels were returned to normal daily
rations.
Experiment III - Utilizing the knowledge gained in
experiments one and twos experiment three was designed to
rapidly condition the test animals showing a clear aversion
to a specific food.
The lithium chloride was combined with
the test food in such a '\vay as to insure an even
distribution of the toxin and prevent any possibility of
separation of the toxin from the food.
The control or
safe food was offered along with the test food during both
the test and retest portions of the experiment.
The subjects in this experiment \vere eight fox
squirrels Gamma, Epsilon, Eta and Kappa served as the
control animals while Delta, Zeta, Theta and Lambda were
the test animals.
The food preference established for these squirrels
was as follows:
More preferred - walnuts
prunes (sun dried)
oranges
dates (sun dried)
apples
grapes (all types)
56
whole corn
Less preferred- celery
Dates were chosen as the test food and a combination
of apple, whole corn and celery served as the control
The Ln
food~
50 of lithium chloride previously computed for each
animal (Table 4) was used in this experiment as it had been
in experiments one and two.
On day 0 all food was removed for twenty-f. 1r hours.
On days 1-3 each animal received 18.0 grams of dates, 30
grams of whole corn, 30 grams of celery and 20 grams of
apple.
On day Lt. each of t:he test animals was given 17.6
grams of dates treated with
chloride.
0.4 gram of powdered lithium
The test (poison) dates were prepared by first
halving them and removing the seed.
The contents of the
dates were then scraped from the outer epidermal layer and
thoroughly mixed with powdered lithium chloride (0.2 gram
per date; t'i10 dates minus their seeds equaled 17.6 grams).
The mixture of date meat and toxin \vas pressed back into
the outer epideDnal layer and the date halves \vere pressed
back together, giving the appearance of whole dates.
The
control animals received 18.0 grams of untreated dates,
which had been altered in a similar manner.
In addition
to the dates each animal received 30 grams of whole corn,
30 grams of celery and 20 grams of apple.
On day 5 the
results of feeding on the poison bait were recorded.
The
remaining treated dates were removed and each animal was
57
re-offered 18.0 grams of untreated dates, 30 grams of
whole corn, 30 grams of celery and 20 grams of apple.
On
day 6, the results of the retest were recorded and each
animal was re-supplied with the same retest ration as on
day 5.
On days 7 through 10, each squirrel received the
same retest ration as on day 5 and the results of feeding
were recorded on the following day.
returned to normal rations on day 11.
The squirrels were
On day 14, each
animal was again offered a retest ration of dates, corn,
celery and apple.
On day 15, the results of the retest
were recorded and the animals were reterned to normal
rations.
Control Animals- Alpha and Iota were not used as test
animals in any experiment.
These animals served as
controls on the after effects of lithium chloride on the
test animals throughout their captivity.
Mu served as a
control on the effects of the laboratory environment on the
experimental squirrels (both test and control) and was not
used in any experiment.
58
RESULTS
Field Experiment
Data Analysis- The data collected during this field
experiment have been assembled into tables 5 through 10.
Specific information regarding the length of damage in a
particular sampling unit and the specific sampling unit
attacked in any given site is contained in these tables.
The majority of the attacks sustained by the sampling
units consisted of tooth marks which cut across the
diameter of the cable.
Each of these tooth marked areas
was considered an attack, but unless the gnawing had
penetrated the outer insulation the tooth marks \vere not
considered damage.
During the period of April 27. 1978, through June 13,
1978, none of the sampling units in the tes·t areas \vere
attacked.
The Columbus control site suffered a total of
14 attacks in three separate control lengths.
The Nestle
control site suffered a total of 9 attacks in three
separate lengths.
The Corbin-Redwing control site incurred
2 attacks in one length (Table 5).
During the period of June 14, 1978 through July 13,
1978, the test and control sheaths began to show attacks in
the Murietta-Costello test site.
This site suffered a
total of 10 attacks in three different, but adiacent,
sheaths.
The Columbus site continued to be attacked,
sustaining 8 attacks in five of its control lengths.
No
59
TABLE 5.
Attacks and damage sustained by sampling units
from April 27, 1978 through June 13, 1978.
Costella-Colbath - No data
Murietta-Costello - No data
Andasol Avenue - No data
Columbus Avenue
Sample Type
Sample No.
No. of Attacks
Length of Damage
Control
3
7
2 in.
Control
4
6
3 1/8 in.
Control
5
1
1 in.
Nestle Avenue
Sample Type
Sample No.
No. of Attacks
Control
5
4
Control
6
4
Control
9
1
Length of Damage
1 !·
3 I.,.
in.
1 ine
li8 in.
Corbin-Redwing
Sample Type
Control
Sample No.
4
No. of Attacks
2
Length of Damage
1/4 in.
'
'
60
TABLE 6.
Attacks and damage sustained by sampling units
from June 14, 1978 through July 13, 1978.
Costello-Colbath - No data
Andasol Avenue - No data
Nestle Avenue - No data
Corbin-Redwing - No data
Murietta-Costello
Sample Type
Test
Test-Control
Test
Sample No.
No. of Attacks
Length of Damage
8
1
3/4 i.n.
9
1
1/8 tn.
10
8
3
1/8 in.
Columbus Avenue
Sample Type
Sample No.
No. of Attacks
Length of Damage
Control
1
1
1/8 in.
Control
3
2
2 1/8 in.
Control
4
2
1 1/2 in.
Control
5
1
1 1/2 in.
Control
8
2
1/4 in.
61
TABLE 7.
Attacks and damage sustained by sampling units
from July 14, 1978 through September 21, 1978.
Andasol Avenue
No data
Castello-Colbath
Sample Type
Test-Control
Sample No.
2
No. of Attacks
2
Length of Damage
5/8 i.n.
Murietta~Costello
Sample Type
Sample No.
No. of Attacks
Length of Damage
Test
4
2
1/4 in.
Test
5
1
3/4 in.
Test-Control
6
1
1/2 in.
Test-Control
7
2
1/4 in.
Test
8
8
1 1/2 in.
Test
10
3
1 1/2 in.
Columbus Avenue
Sample Type
Sample No.
No. of Attacks
Length of Damage
Control
1
3
3/8 in.
Control
2
1
1/8 in.
Control
4
2
5/8 in.
Control
.J
....
2
1/2 in.
Control
6
6
2 1/4 in.
Control
7
5
5/8 in.
Control
9
6
7/8 in.
62
TABLE
7. Continued
Nestle Avenue
Sample Type
Sample No.
No. of Attacks
Length of Damage
Control
7
1
1/8 in.
Control
8
1
1/8 in.
Corbin-Redwing
Sample Type
Sample No.
No. of Attacks
Length of Damage
Control
3
1
1/8 in.
Control
5
1
1/8 in.
Control
6
2
3/8 in.
63
TABLE 8.
Attacks arid damage sustained by sampli.ng units
from September 22, 1978 through November 21,
1978.
Costello-Colbath - No data
Andaso 1 Avenue
No data
.·
Nestle Avenue - No data
-
Corbin-Redwing - No data
Murietta-Costello
Sample Type
Sample No.
No. of Attacks
Length of Damage
1
3
1 3/8 in.
Test-Control
2
2
5/8 in.
Test-Control
7
1
1/2 in.
8
2
2
9
2
1 1/4 in.
Test
Test
Test-Control
l/4 in.
Columbus Avenue
Sample Type
Sample No.
No. of Attacks
Length of Damage
Control
1
1
1/8 in.
Control
3
2
7/8 in.
Control
4
10
1 7/8 in.
Control
5
2
Control
6
3
Control
7
4
1 in.
3/4 in.
1 in.
64
TABLE 9.
A summary of the attacks and damage sustained by
sampling units from April 27, 1978 through
November 21, 1978.
TEST AREAS
Castello-Colbath
Total Attacks
2
Length of Damage
Penetrations of Outer
Cable Insulation
5/8 in.
0
Murtetta-Costello
Tota 1 Attacks
37
Length of Damage
Penetrations of Outer
Ca1>le Insulation
12 1/2 in.
0
Andasol Avenue
Total Attacks
Length of Damage
Penetrations of Outer
Cable Insulation
0
0
0
CONTROL AREAS
Columbus Avenue
Total Attacks
69
Length of Damage
Penetrations of Outer
Cable Insulation
21 7/8 in.
34
Nestle Avenue
Total Attacks
11
LeP~th
of Damage
Penetrations of Outer
Cable Insulation
2 1/8 in.
6
Corbin-Redwing
Total Attacks
6
Length of Damage
7/8 in.
Penetrations of Outer
Cable Insulation
0
65
TABLE 10.
A comparison of the number of attacks and
damage sustained by test and control sites.
TEST SITES
ATTACKS
Control Sheaths
DAMAGE
Test Sheaths
11
Total
Times Cable
Damaged
39
0
28
CONTROL SITES
ATTACKS
DAMAGE
Control Lengths
Total
Times Cable
Damaged
86
86
40
DAMAGE TO CABLE
Damage per Attack
Control Areas
Test Areas
Percent Damaged
40/86
46.5 %
0/39
0.0 %
66
other damage was recorded in any other site (Table 6).
The period of July 14, 1978 through September 21,
1978, was the most productive time period for the
generation of data with all of the sites suffering attacks
except Andasol.
The Castello-Colbath site incurred 2
attacks in one sheath.
The Hurietta-Costello site was
attacked 17 times in six different sheaths.
The Columbus
site suffered a total of 25 attacks in eight of its
lengths.
The Nestle site incurred 1 attack in each of two
control lengths.
The Corbin-Redwing site sustained a
total of 4 attacks in three separate control lengths
(Table 7).
During the period of September 22, 1978, through
November 21, 1978, only the Nurietta-Costello and Columbus
sites incurred any damage.
The Murietta-Costello site
suffered a total of 10 attacks in five separate sheaths.
The Columbus site suffered a total of 22 attacks in six
of its control lengths.
Statistical Analysis - The field data were analyzed using
various statistical techniques to determine the
significance of the observed differences between the test
and control sites.
The Andasol Avenue test site was not
included in this analysis to avoid prejudicing the data in
favor of the test sites.
These data were analyzed using the Poisson
distribution (Sokal and Rohlf, 1969), based on the
67
assumption that a bite is a rare event, given the total
number of cable lengths available in the test and control
sites.
The data were analyzed in several lvays to
determine if there lvere differences between the protected
and unprotected cables in distributions of bites (attacks).
The combined total of attacks in test and control sites
were first lumped together and the following descriptive
statistics were obtained: standard deviation = 4.0419,
mean= 2.5000, coefficient of variation= 161.6748,
coefficient of dispersion= 6.5347.
The Poisson
distribution revealed that the attacks were clumped, which
is supported by the value obtained for the coefficient of
dispersion of 6.5347.
Separate frequency tables were then
established for the test and control sites.
Poisson
distributions were then used to determine if the bites
were clumped in both test and control sites.
The
following descriptive sta·tis·tics were obtained for the
control sites' mean
= 2.8333,
standard deviation
= 4.5035,
coefficient of variation= 158.9661, coefficient of
dispersion= 7.1591.
The Poisson distribution for the
control sites was clumped, which is supported by the
coefficient of dispersion of 7.1591.
The following
descriptive statistics were obtained for the test sites=
mean= 1.9500, standard deviation= 4.5035, coefficient of
variation = 169.2462, coefficient of dispersion = 5.5856.
The Poisson distribution again revealed that the bites were
68
clumped, which was supported by to coefficient of
dispersion of 5.5856.
A two by two test for independence (using the Gstatistic) using the Yates correction (Sokal and Rohlf,
1969), with no cell less than five, was employed to test
whether the number of sampling units attacked was
indeper.dent of the type of site (test or control) in which
it was located.
for Gadj of 0.03
indicated that the number of sampling units attacked \vas
A value
obt~ined
independent of the site in which it was loca-ted.
This test
was also used to determine whether the sampling units
which were overhung by vegetation were attacked more often
than those which were in the open.
A value for Gadj of
2.102 indicated that the number of sampling units attacked
was independent of overhanging vegetation.
The large difference in the number of attacks
sustained by sampling units which were overhung by
vegetation (n
= 88)
and those which were in the open (n =
37), was analyzed with the aid of at-test.
The value
obtained forts of 3.4677 was significant at: the 0.01 level
(Rohlf and Sokal, 1969).
A arcsine test for equality of two percentages
(Sokal and Rohlf, 1969) was used to determine the
significance of the observed differences between the
percent of damage by test and control sites.
69
Site
n
Damage
Attacks
Percent Damaged
Control
30
40
86
46.5
20
0
39
o.o
Test
The test (ts = 7.4456, p
< 0.001)
indicated that the
difference in damage at the two sites was highly
significant.
70
Laboratory Experiments
Experiment I- On days 1-4, the squirrels consumed all of
the filberts within the first thirty minutes of the test
period.
Only after consuming all of the filberts, did
any animal consume any of the whole corn or rolled oats.
The rolled oats were left untouched until day 3, when
Alpha and Epsilon ate approximately one half of the
quanity offered.
On day 4, all of the animals were feeding
to some extent on the rolled oats.
The fox squirrels consumed only a portion of the
corn seed, the embryo and cotyledon, while leaving the
endosperm untouched.
The remaining endosperm was, on
occasion, discarded onto the floor of the laboratory.
The
squi.rrels sometimes spilled portions of the corn and oats
onto the lab floor.
The spillage and discards from
several cages became mixed to the extent that only a
visual estimate of the amount of these foods consumed was
possible.
The filberts were either eaten in1mediately or
were left in such large pieces that they would not fit
through the wire mesh and so were seldom lost due to
spillage or discarding.
The amount of filberts consumed on day 5, at the
first toxicity level tested (0.1 gram LiCl/ 8.2 grams of
filberts), differed.
The control animals continued to feed
as on days 1 through 4, consuming 8.3 grams or 100% of the
71
test food offered.
The test animals have reduced their
consumption somewhat; Gamma, 6.2 grams or 75%; Delta, 6.4
grams or 77%; Epsilon, 7.8 grams or 94%; Zeta, 7.0 grams
or 84% of the test food offered (Table 11 and Figure 10).
The amount of lithium chloride ingested as a result of
feeding on the poison bait was as follows:
Gamma, 0.08
grams or 14% of an LD 50 ; Delta, 0.08 grams or 14% of an
Ln 50 ; Zeta, 0.08 grams or 14% of an LD 50 ; Epsilon, 0.09
grams or 18% of an Ln 50 (Table 11 and Figure 11). The
amount of li<chium chloride ingested is only approximate,
as it was calculated from the amount of food consumed and
assumes an even distribution of the toxin throughout the
test food, i.e., Zeta consumed 7.0 grams/8.3 grams or 84%
of the filberts offered; 84% of 0.10 grams of LiCl equals
0.08 grams and dividing by 0.58 grams (an LD 50 for Zeta)
equals a 14% LD 50 of LiCl ingested by Zeta.
The results of the
r~test
on day 6 were as follows:
Epsilon consumed 7.8 grams or 94% of the filberts offered.
The remaining animals (test and control) consumed 8.3 grams
or 100% of the filberts offered.
The amount of filberts consumed on day 8, at the
second toxicity level tested (0.3 gram LiCl/8.0 grams of
filberts), were as follows:
Gamma, 1.0 gram or 12%; Delta,
2.9 grams or 35%; Epsilon, 2.6 grams or 31%; Zeta, 2.8
grams or 34%; Alpha, 6.8 grams or 82%; Beta, 8.3 grams or
100% of the test food offered (Table 11 and Figure 10).
-
-
-
-
--·-
-
-
72
---
TABLE 11.
-
--
----
-
Percent LD 50 of LiCl Consumed/ Percent of Tes~
Food Consumed for laboratory experiment number
one.
ANIMAL
Day No.
Alpha
Beta
Gamma
Delta
Epsilon
Zeta
1
0/100
0/100
0/1oo·
0/100
0/100
0/100
2
0/100
0/100
0/100
0/100
0/100
0/100
3
0/100
0/100
0/100
0/100
0/100
0/100
4
0/100
0/100
0/100
0/100
0/100
0/100
5
0/100
0/100
14/75
14/77
18/94
14/84
6
0/100
0/100
0/100
0/100
0/94
0/100
7
0/0
0/0
0/0
0/0
0/0
0/0
8
0/82
0/100
7/12
18/35
18/31
17/34
9
0/100
0/100
0/100
0/100
0/100
0/100
10
0/0
0/0
0/0
0/0
0/0
0/0
11
0/100
0/100
5/11
18/33
0/0
9/17
12
0/100
0/100
0/53
0/47
0/20
0/32
13
0/0
0/0
0/0
0/0
0/0
0/0
73
FIGURE 10.
The feeding behavior of six fox squirrels
(Sciurus niger), at the three different levels
of toxicity, which were tested in experiment
number one. The squirrels did not receive any
test food on days 7 and 10 and the gaps in the
graph are to so indicate.
. _ ...
.•
100
90
80
-...,
c
ALPHA
70
...u
60
I
::!E
EPSILON-
• zETA
Q
w
rET A
GAMMA ••••••
I DELTA
CD
a.
.5
I
•••••••
50
::;,
(/)
z
0
0
40
Q
0
0
u.
30
1-
(/)
w
1-
20
... ' ....
.. ...
.. ..
.....
.... .
..
I
.
..
-: ,.:.·
:./.
,
'
.....
.
10
.
..•. ••••
.•
....
......
:.
~.v-
•
0
1
2
3
4
5
6
TIME
7
8
9
10
11
12
13
in 24 hour periods )
"
~
75
FIGURE 11.
The percentage of an LD 50 for lithium chloride
consumed by the test squ~rrels during the three
separate tests of experiment number one.
-----
-.:y----
0
76
VWWV9
V.L130
I
l
--
N
N01lSd3
0
V.L3Z
w
I
a:
w
u..
u..
0
0
\1WWV!:>
0
0
I
u..
NO:~~~: : -~-;-~----sj {~l
0
V.L'3Z
c-----·----1
. . _ __=~-----
V.L130
N011Sd3
C.__
___________--li
V.L3Z
L
L---------------~
...
It)
0
C')
03WOSNO:> 1:>!1
L~------tj
JO
0Sa1
.LN3:>H3d
...
0
0
77
The amount of lithium chloride ingested as a result of
feeding on the poison bait was as follows:
Gamma, 0.04
grams or 7% of an Ln 50 ; Delta, 0.10 grams or 18% of an
Ln 50 ; Epsilon, 0.09 grams or 18% of an Ln 50 ; Zeta, 0.10
grams or 17% of an Ln 50 (Table 11 and Figure 11).
The results of the retest on day 9 did not indicate
any aversion to filberts, as both the test and control
squirrels consumed 8.3 grams or 100% of the filberts
.
offered. The test animals, however, did show some
reluctance to begin feeding, with none of the test animals
feeding on the filberts during the fir8t hour of the retest
and some quantity of filberts remaining i.n all of
th(~
test
cages during the eighth hour of the retest.
The amount of filberts consumed on day 11, at the
third toxicity level tested (0.3 gram LiCl/7.2 grams of
filberts), was as follows:
Gamma, 0.8 grams or 1.1%, Delta,
2.5 grams or 33%; Epsilon, 0.0 gram or 0%; Zeta, 1.3 grams
or 17%; Alpha, 7.5 grams or 100%;
(Table 11 and Figure 10).
Beta~
7.5 grams or 100%
The amount of lithium chloride
ingested as a result of feeding on the poison bait was as
Gamma, 0.03 grams or 5% of an LD 50 ; Delta, 0.10
grams or 18% of an Ln 50 ; Epsilon, 0.00 grams or 0% of an
follows:
Ln 50 ; Zeta 0.05 gram or 9% of an Ln 50
Figure 11).
(Table 11 and
The results of the retest on day 12 were as follows:
Alpha, 7.5 grams or 100%; Beta, 7.5 grams or 100%; Zeta,
78
2.4 grams or 32%; Epsilon, 1.5 grams or 20%; Gamma, 4.0
grams or 53%; Delta, 3.5 grams or 47% of the test food
offered (Table 11 and Figure 10).
Since these results
indicated some avoidance behavior, I chose to end the
experiment at this point.
Experiment II- At the last toxicity level tested in
experiment one, I observed that the animals stopped feeding
after penetrating the core of one or two filbert nuts.
Apparently the animals were either reacting to the
concentration of the lithium chloride in the center of the
nuts or the toxin was reacting very rapidly within the
body of these animals.
I, therefore, sought a new method
of presenting the toxin.
Mixing of the lithium chloride
with the peanut butter was twofold in purpose.
One, it
would allow the toxin to spread over a larger area of the
food; two, it might allow more of the toxin to be
iP~ested,
by slowing the absorption time of the lithium ion as a
result of slow digestion of the peanut butter.
I felt
that if a larger percent of an Ln 50 of lithium chloride
were ingested a more rapid conditioning would occur.
On days 1 through 3, all of the test animals
consumed the filberts and peanut butter before feeding on
any of the other foods.
My notes on day 1 show:
.,Beta picked up a filbert nut, smelled it, licked
the peanut butter, split the nut in half and ate the
peanut butter first.
After consuming the peanut butter,
79
Beta proceeded to eat the filbert nut.
a second nut and repeated the behavior.
She then picked up
After eating all
of the filberts, Beta drank some water and began to feed
on the whole corn."
The results of feeding on day 4 (first poisoning of
experiment two) varied cosiderably between individual
animals.
The control animals, Lambda and Iota, continued
to feed as on days 1 through 3, consuming 7.0 grams or
100% of the filberts and peanut butter offered.
The test
animals consumed the following amounts: Beta, 7.0 grams or
100%; Eta, 7.0 grams or 100%; Theta, 2.6 grams or 37%;
Kappa, 2.7 grams or 39% of the test food offered.
The
amount of lithium chloride consumed as a result of feeding
on the poison bait was as follows: Beta, 0.3 grams or fJ-3%
of an Ln 50 ; Eta, 0.3 grams or 53% of an Ln 50 ; Theta, 0.1
grams or 17% of an Ln 50 ; Kappa, 0.1 grams or 16% of an
LD 50 •
The amount of lithium chloride ingested was
calculated in the same manner as in experiment one.
My
notes on day 4 show:
"Beta began feeding on the filberts immediately.
---she split open one of the filbert nuts and proceeded to
eat the peanut butter first.
the filbert nut.
She then consumed·most of
Suddenly she began to rub the sides of
her mouth on the cage floor.
She rubbed both sides of her
mouth repeatedly on the cage floor.
Beta then entered her
nest (glass jar) and laid down, remaining quiet for the
80
remainder of my stay in the lab (about 30 minutes)."
On days 6 through 9, the squirrels received normal
rations of food, which included apple, peanuts, walnuts,
oranges, whole corn and rolled oats.
The squirrels
received these rations to eliminate any possibility that
feeding on the poison bait was due to the semi-starved
conditions of experiment one.
Observations of the feeding on the normal diet
revealed that the animals were refusing to eat peanuts.
The apparent association of the flavor of peanut butter
i.vith the peanuts was not suprising in itself, but was
however, unexpected.
Th.e amount of filberts consumed on day 10 (second
poisoning of experiment two) was as follows: Beta, 7.0
grams or 100%; Eta, 4.7 grams or 67%; Theta, 2.7 grams or
39%; Kappa, 4.0 grams or 57%; Lambda, 7.0 grams or 100%;
Iota, 7.0 grams or 100%.
The amount of lithium chloride
consumed could not be determined and the above figures for
the ·test food consumed are somewhat in error. as some of
the peanut butter was smeared on the cage wire and bits of
pearrut butter were found in the sub-floor of the test
cages.
Hy notes on day 10 show:
'!Beta began to feed on the filberts almost as soon
as they were offered.
She picked up one of the filberts
and began to devour the outside of the nut and did not
eat the peanut butter first as she did during the first
81
poison test.
After consuming a portion of one nut, she
began rubbing her mouth on the floor of the cage.
After a
few minutes passed, she returned to her nest and laid down.
Beta did not attempt to feed again during the remainder of
my stay in the lab."
All of the test animals refused to eat peanuts on
days 11 and 12.
The control animals consumed a normal
ration of food, including peanuts.
The results of the retest on day 13 were as follows:
Iota, 7.0 grams or 100%; Lambda, 7.0 grams or 100%; Beta,
1.0 grams or 100%; Eta, 7.0 grams or 100%; Theta, 6.2
grams or 89%; Kappa, 2.9 grams or 41% of the test food
offered.
Again, these numbers contain some inaccuracy as
some of the peanut butter was again found on the cage wire
and bits of· peanut butter were lost into the sub-floor of
the cages of the test animals.
My notes on day 13 show:
"Beta smelled the dish containing the filberts,
smelled the filberts, drank some water, picked up and ate
half of one nut, rubbed her mouth on the cage floor again
and again and then laid down in her nest."
The squirrels were offered peanuts as part of the
normal ration of food on days 14 and 15.
They were
refused by the test animals, but were eaten by the control
animals.
The amount of filberts consumed on day 16 (third
poison test of experiment two) was as follows: Beta, 7.0
82
grams or 100%; Eta, 6.0 grams or 86%; Theta, 5.9 grams or
84%; Kappa, 5.0 grams or 71%; Iota, 7.0 grams or 100%;
Lambda, 7.0 grams or 100%.
Beta made no attempt to feed
during my stay in the lab (about 60 minutes).
All of the test animals refused to eat peanuts on
days 17 and 18, when they were provided with normal
rations.
The control animal Lambda consumed a normal
ration of all foods, including peanuts.
Iota did not feed
on day 17 and died on day 18 after chewing the wire in the
floor of her cage.
The amount of filberts consumed during the retest on
day 19 was as follows: Beta, 5.9 grams or 84%; Eta, 7.0
grams or 100%; Theta, 7.0 grams or 100%; Kappa, 4.3 grams
or 61%; Lambda, 7.0 grams or 100%.
When I examined the data from experiment two, I
.realized that most of it did not make any sense.
Had the
test squirrels consumed the dosage of lithium chloride
indicated by the calculations, all of them should have
been conditioned.
However, only Kappa showed any
reasonable response to the poisonings and that '\vas an
unclear conditioning at best.
was toward peanuts.
The only clear conditioning
Why hadn't the animals avoided the
filberts, when they were the original source of any ill
effects, which the animals had experienced?
In an attempt
to solve this problem, I decided to try feeding Beta a
more toxic dose and to observe her reaction to the toxin
83
at very high levels.
A special dose of lithium chloride was prepared for
A concentration of 0.7 grams (an Ln 50 for Beta) of
lithium chloride contained in 2.0 grams of peanut butter
Beta.
was placed between the halves of eight filbert nuts,
weighing 12.0 grams, for a total of 14.7 grams of test
food.
Beta was presented with the lethal dose of lithium
chloride and closely observed while she fed.
Hy notes
show:
"Beta picked up one of the filbert nuts and through
careful manipulation, began to chew the filbert in such a
manner as to totally remove all of the peanut butter from
the filbert nut.
The chewing was parallel to the broken
edge of the nut, on which the peanut butter was spread,
similar to an orange being peeled.
Some of the filbert
nut was left attached to the peanut butter.
As Beta
gnawed the filbert, some of the peanut butter became stuck
to her 'vhiskers and forearms.
After consuming the nut,
Beta carefully wiped the peanut butter from her ·whiskers
and forearms on the wire of the cage.
Only after all of
the peanut butter was removed did she groom her fur.
After feeding on the first nut, Beta drank some water and
laid down in her nest for 38 minutes.
After this rest
period, she resumed feeding on the remaining nuts,
followir~
the previous behavior pattern, but without the
rest period.
84
The test squirrels were watched carefully over the
remaining seven months of their captivity for
extinction of the aversion to peanuts.
of
~igns
As peanuts were a
part of the daily diet of all of the squirrels, the
animals were retested on a daily basis for their response
toward the peanuts.
Ten days after the final poisoning of
experiment two, Kappa began to feed to some extent on the
peanuts.
By the twenty-third day aft.er the final
poisoning, Kappa had returned to a full daily ration of
peanuts (about 10 grams).
Eta and Beta refused to eat
peanuts, even when deprived of food for twenty·,four hours.
Theta would consume peanuts when deprived of food for
twenty-four hours and given no other food source.
however, would not eat peanuts if
provi~ed
Theta~
with an
alternative food source.
Experiment III - On days 1 through 3, the squirrels were
offered 18.0 grams of dates, 30 grams of whole corn, 30
grams of celery and 2.0 grams of apple.
Each of the
animals con.3umed 18.0 grams of dates each day, as well as,
portions of the other foods offered, with the following
exceptions: Kappa, on day 4, consumed 15.7 grams of dates
or 87%; Theta, on days 2 and 3, consumed 16.6 grams of
dates or 92% and 16.4 grams of dates or 91%, respectively.
On day 5, the results of feeding on the treated
dates were as follows: Eta,. 18.0 grams or 100%; Gamma, 18.0
grams or 100%; Kappa, 18.0 grams or 100%; Epsilon, 13.5
85
grams or 75%; Lambda, 13.0 grams or 72%; Theta, 10.8 grams
or 60%; Zeta, 11.3 grams or 63%; Delta, 13.5 grams or 75%
(Table 12 and Figure 12).
The amount of lithium chloride
ingested as a result of feeding on the poison bait was as
follows: Lambda, 0.17 gram or 58% of an LD 50 ; Theta, 0.12
gram or 40% of an LD 50 ; Zeta, 0.13 gram or 43% of an LD 50 ;
Delta, 0.16 gram or 53% of an LD 50 (Figure 13).
On days 5 through 9, the squirrels were provided with
18.0 grams of untreated dates, 30 grams of corn, 30 grams
of celery and 20 grams of apple.
The test animals all
refused to feed on the dates on days 5 through 9, with the
following exception that on day 5 Delta consumed 7.9 grams
or 44% of the dates ot'fered.
The control animals
continued to consume 18.0 grams of dates on days 5 through
9, with the follmving exceptions; Gamma consumed 12.1
grams or 67% of the dates offered on day 5 and Kappa
\._
consumed 16.0 grams or 89% of the dates offered on day 8
and 13.3 grams or 74% of the dates offered on day 9.
The squirrels were returned to normal rations on days
10 through 13.
On day 14, the squirrels were again
retested as on days 5 through 9.
The results of the retest
showed that the test animals refused to feed on the dates,
but did consume normal rations of the other foods provided.
The control animals, however, continued to feed as on day
1, consuming 18.0 grams or 100% of the dates provided, in
addition to portions of the other foods offered.
86
TABLE 12..
'l'·est food consumption in experiment number
three.
TEST FOOD CONSUMED (IN PERCENT)
...
.. , .
Test Day
Animal
1
2
3
4
5
6
7
8
9
ETA
100
100
100
100
100
100
100
100
100
GAMMA
100
100
100
100
67
100
100
100
100
KAPPA
100
100
87
100
100
100
100
89
74
EPSILON
100
100
100
75
100
100
100
100
100
LAMBDA
100
100
100
72
0
0
0
0
0
THETA
100
92
91
60
0
0
0
0
0
ZETA
100
100
100
63
0
0
0
0
0
DELTA
100
100
100
75
44
0
0
0
0
87
FIGURE 12.
The feeding behavior of eight fox squirrels
(Sciurus niger) at the toxicity level of LiCl
tested in experiment number three.
100
-=r ;: '
········$··~~·····~···~
••••••••••••••••••....!.!.!..!..•~o•:.. •
;::g ==+ ·=~'E;•;;;;;;;;;;;;~~::.0.~
0
0
0.
0
0
~\··
•..v•
\
90
•••••••o~ •• Ql.
'
•
f)
·~000
·. •• ·. •
••
• \ .
• 00
•
a:
w
0..
c
:IS
50
GAMMA
•• •• ·0•
I
I
II
·......
..• \'vII
•• •
·.•·.,..·.. ..
..• . .·.
•
0
•
•
0
:~··
•
.•.
0
....•.
.•.
I EPSILON~-
••
••
0
.•..•.
•• 0
40
I
0
0
•••••
DELTA
••••
30
•
.•.
••
••
••
••
•
:~·.
THETA
ZETA
1.1.
\
·-
\
·~~·.
0
1-
\
LAMBDA
z
0
I
ETA
KAPPA
::)
Cl)
0
\
--
.
60
0
w
/
0
•
0
;
.0
•
•
70
\
•
•
w
I
0
•
....z
;
,
\ /
·. .... .
··.:·
•
80
I
\\
00
•••
·----I
I
I
.......
....
.....
.......
......
......
...,........
......0.
• •0
• •0
CI)
w
1-
20
0
2
3
4
5
TIME
••
·0.:·.·
••
••
••
••
••
••
••
6
7
•o
10
•
8
9
10
(in 24 HOUR PERIODS)
00
00
89
FIGURE 13.
The percentage of an Ln 50 for LiCl consumed
by the test squirrels during experiment
number three.
90
...
·.:
.
_.-
,.______
0
w
a:
w
u.
u.
0
\U130
,
0
0
0
u.
:fl)
r-.: ~
... a:
I
"
VBZ
""""""fl)
cn_
'Ot 0
0 ::;
,------
~
~
-
'
I
0
co
CJ
V!3Hl.
V08WV1
0
II)
0
'Ot
0
t?
0
N
03WnSNO:> 1:>!1 JO OS01 l.N3:ll::l3d
,..
0
0
91
DISCUSSION AND CONCLUSIONS
Avoidance behavior can result when an animal has
learned, through trial and error, to respond in a negative
manner to some external stimulus.
Many times, this
behavior is the direct result of an animal having been
punished by one of the many protective devices employed by
plant and animal species as an anti-predator strategy,
e.g., poisons, thorns, teeth; claws, chemical irritants,
stings, venom, etc.
Some species of plants and animals
advertise their ability to protect themselves through the
use of various warning devices, e.g., rattling or buzzing
sounds, bright coloration, distinctive co1.or patterns,
chemical odors, body posture, etc.
Predators perceive
these warning devices ·through their sensory organs as
something to be avoided, usually as a result of previous
contact with that species
(Brower~
1969, Cott,
1940~
Grant,
1963).
Wilcoxon et al* (1971) in experimenting vlith illness
induced aversions in laboratory rats and bobwhU:e quai 1
(Colinus virginianus) found that a visual cue alone could
avert quail, but not rats, from drinking colored water
which had been paired with illness.
Both the quail and
rat could associate gustatory cues with illness and would
avoid flavored water which had been paired with illness.
When both cues were present, however, the quail relied on
------
92
the visual cue alone and would not, later, avoid water with
the flavor'a.s the only warning device,
These workers
suggested that a diurnal bird with a highly developed
visual system such as the quail would probably have to
evolve such an ability due to the high reliance placed on
vision in their daily foraging.
Toads {Bufo terrestris) use their visual sense to
avoid honeybees (Apis mellifera) and any insect with a
similar appearance (mimics) after an initial contact with
that insect (J. Brower and L. Brower, 1962).
These toads
will also avoid bumblebees (Bombus americanorum) and their
mimics (L. Brovler et al., 1960) after an initial contact
with that species.
Birds will avoid insects which they have found
unpalatable and \vi 11 also avoid mimics of such insects
{J, Brower, 1958a, 1958b, 1960; L. Brower, 1969; Morrell
and Turner,
of mimicry
1970~
Linsley et al., 1961).
contc:~ins
The literature
many such examples which serve to
point out that an ;\D.imal learns which things in its
surroundings to accept or reject as a food source.
Those
individuals within a population which have neither the
genetic programming nor the capacity to learn to avoid
poisonous or dangerous species are quickly removed, by
natural selection from the gene pool.
Nan has long used poison for plant and animal
control.
Extremely lethal poisons are generally not
93
effective over long periods of time as they usually remove
'
all of the-affected individuals from the gene pool.
Selecti.on by man has resulted in plants and animals which
are virtually immune to certain types of poison.
The
classic example of the housefly's (Musca domestica)
resistance to DDT is well known.
Selection of this type
has occ11rred in coyotes (Canis latrans) which have
developed an ability to smell various poisonous substances
such as strychnine and to detect the odor of a buried
steel trap.
An alternative approach, as suggested by Gust:.avson
et al. (1974), would be to use an animal's evolved
behavior for its control.
Avoidance behavior thrnugh
aversive conditioning is a principle which has been sbc•.m
to be an effective means of animal control.
The advantage
to this type of control is that affected individuals are
not removed from the g-ene poo 1 and, thus, the character
remains in the population.
Therefore, selection against
certain individuals is not occurring and the control
should operate over a long period of time.
Gustavson et
a1~
(1974) used lithium chloride mixed
with mutton, followed by an intraperitoneal injection of
lithium chloride, to condition coyotes against killing
sheep.
The lithium illness induced apparent nausea,
vomiting and lethargy in the coyote, with the result that
these animals would not attack live sheep, but did attack
94
an alternative prey (rabbits), showing that the animals
were hungry and that the aversion was specific for sheep.
In a later study, Gustavson et al. (1976) found the same
results could be attained with lithium treated baits
alone.
In laboratory experiments, these workers were able
to condition coyotes against preying on rabbits, wolves
(Canis lupus) against preying on sheep and a cougar (Felis
concolor) against feeding on venison.
In the field
experiment conducted on a sheep ranch in southwestern
Washington, a significant reduction of coyote predation on
sheep was achieved when the area surrounding the flocks was
baited with lithium treated sheep carcasses and sheep
flavored baits.
Ellins et al. (1977) used a similar technique to
reduce coyote predation on sheep in the Antelope Valley of
California.
These workers injected lithium chloride
solutions both intramuscularly and intraperitoneally into
sheep carcasses which were then left as bait in areas used
''for sheep pasture.
The baiting was carried out prior to
" and during occupancy of these areas by sheep flocks •
0
This
·baiting technique resulted in a ·significant reduction in
coyote predation on these sheep flocks.
During the second
year of this study (Ellins and Catalano, 1979) the number
of sheep taken by coyotes was reduced below the previous
year.
The technique was then expanded to include turkey
farms in the same area.
Turkey carcasses treated with
95
lithium chloride were placed near two turkey farms, with
the result. that coyote predation on turkeys was reduced to
less than half of the previous year's kill.
Brett et al. (1976) were sucessful in conditioning
buteo hawks against killing and eating mice.
Red-tailed
hawks (Buteo jamaicensis) and one rough-legged hawk (Buteo
lagopus) which received intraperitoneal injections of
lithium chloride after feeding on mice were showr1 to avoid
mice with the same sensory cues (black coat color and a
bitter taste), but would kill and eat mice with an
alternative set of sensory cues (white coat color and a
natural taste).
When these hawks were given both visual
and gustatory cues during the conditioning process! the
aversion to mouse killing required only one treatment.
The visual cue alone required several lithium injecttons to
establish an aversion sufficient for attack suppression.
As a result of these multiple treatments, the hawks became
somewhat averted to the taste of mouse flesh in general.
The reasons for this are apparent in view of the results
obtained in the coyote studies.
The taste cue alone was
sufficient to prevent consumption of the preys but di..d not
supress attack behavior unless a visual difference was
evident.
Rusiniak et al. (1976) were able to condition
laboratory rats against killing and eating mice when
lithium illness immediately followed such behavior.
In
- - - -'
96
the same study, laboratory ferrets (Mustela putorius) were
conditioned against eating mice but could not be averted
from killing them.
The ferrets used their feet to kill
the mice, in lieu of the usual bite to the neck, after
being subjected to lithium illness immediately following
mouse predation.
This is probably a result of a behavior
pattern which does not allow blockage of attack behavior
in the ferret.
Gustavson et al. (1974) proposed a two-phase
conditioning process in mammals for the acquisition of a
taste aversion.
Gustavson et al. (1974:583) stated:
"In phase one, the flavor of food becomes aversive
after one illness, after which the sights and sounds
of the prey may still elicit attack but the aver.sive
flavor inhibits feeding. Phase two occurs when the
auditory, visual, and olfactory cues from the prey
become associated with the now aversive flavor. thus
subsequent attacks are inhibited and perhaps a
second treatment is unnecessary. In some cases
emesis may forge an association between vomited
gustatory cues and odors of the vomitus which is
sufficient for the second phase of conditioning."
I found this statement to be similar to the
"gourmand-gourmet hypothesis" put forth by L. Brower
(1969:26):
"To a na''ive bird flavor conveys no particular
information, so that the bird will eat any food it
finds and is a gourmand. When a bird is made ill by
an insect, it associates the flavor of the insect
with the illness and therafter can reject a similar
insect by tasting it, so that the bird becomes
something of a gourmet. At that level, however, the
bird must still take time to ca·tch the insect.
Hence birds usually learn to reject such insects on
sight, which is the most efficient level of
rejection."
97
The above studies tend to support the results
obtained with the fox squirrel which exhibits the same
ability to learn to avoid poisonous subtances within its
environment after an initial contact with that substance.
The fox squirrel responds primarily to gustatory and
olfactory cues from the poisonous substance which
subsequently is translated into visual discrimination
between safe and poison foods.
This is consistent wit:h
Brower's hypothesis and the two-phase conditioning
proposed by Gustavson and his coworkers.
In the fox squirrel, the strength of the conditioning
seems directly dependent on the amount of lithium chloride
ingested and the severity of the resulting illness.
In
experiment one, consumption of low levels (less than or
equal to 0.10 gram) of lithium chloride required mul·tiple
·treatments to initiate any observed conditioning.
Consumption of as little as 0.08 gram was sufficient to
cause illness in all of the animals tested.
This amount,
therefore, may be thought of as a sick dose-100 (sn 100 ) or
the amount of the toxin required to cause illness in 100%
of the animals tested.
It was, however, insufficient
for one trial conditioning in these animals.
The illness
was expressed in the form of loss of appetite, lethargy
and diarrhea.
I did not observe the fox squirrel to
vomit; however, what appeared to be vomitus was
occasionally observed in the bottem of the cages of the
98
test animals.
The doses used in these experiments may
have been below the amount required to produce vomiting,
or perhaps this animal is incapable of such an action.
In experiment two, the squirrels were shown to form
lang-lasting aversions to a food which had the same
gustatory cue (peanuts) as the food used in the test
(peanut butter).
Although the observation of Beta
comprises a single observation of a single animal, the bits
of peanut butter found in the sub-floors and on the wire in
the cages of the other test squirrels suggest to me that
the other test animals had learned the same technique (or
a similar one) for the removal of the poisonous peanut
butter.
Thus, 1 beli.eve
t~hat:
the test animals had ingested
a sufficient amount of lithium chloride during the first
poison test of experintent:
peanuts and peanut butter.
t\•70
to induce an aversion to
Thereafter the squirrels
simply chewed the peanut butter away from the filbert nuts
and ate them.
The peanuts ''Tere in effect flavor mimics of
the peanut butter and thus an aversion to one should
protect the other.
Perhaps the behavior described is an
instinctive one, which is used in the wild, e.g., to
separate poisonous fruit from and edible seeds or vice
versa.
This, however, is merely conjecture.
Experiment three has shown that the fox squirrel can
be conditioned in one lithium trial and that the aversion
is specific for the food tested or, as in experiment two,
99
one with similar sensory cues.
When the squirrels ingested
between 0.12 and 0.17 gram of lithium chloride as a result
of feeding on the poison bait, they were found to be
conditioned in one lithium trial.
The amount of toxin
ingested was calculated to be between 40 and 58 percent of
an LD 50 for lithium chloride for the individual squirrel
tested. The amount ingested in experiment one was never
over 18 percent of an LD 50 a~d was ineffective as a one
trial dose of lithium chloride. \.Vhen I examined the
amount of lithium chloride administered ·to hawks (Brett et
al., 1976), I found that the amount given to all but one of
these birds was equal to 20 percent of an LD 50 when
calculated in the same manner as for the squirrels.
It is
interesting to note that a rapid extinction of the birds'
conditioning occurred at this level.
On~
of the ha\Jks
received 30 percent of an LD 50 in the black~bitter test
and the conditioning of this bird seemed 1::o me to be more
thorough than the others tested.
The rats used in fhe
Rusiniak et al. (1976a) study received approximately 15 to
18 percent of an LD 50 of lithium chloride when calculated
in the same manner as for the squirrels. These rats
required multiple treatments to show an effective aversion
to mouse killing.
In experiment two, the fox squirrels which ingested
large doses of lithium chloride (Beta, 43%; Eta 53%)
showed no extinction of the aversion even after seven
100
months of testing.
The squirrels which had ingested
lesser amounts (Theta, 17%; Kappa, 16%) showed marked
differences in their extinction of the aversion to peanuts.
Kappa had begun to feed on the peanuts after ten days and
had returned to baseline levels within twenty-three days
after the final poisoning.
Theta refused to eat peanuts
unless she had been deprived of food for twenty-four hours.
Kappa's reaction was similar to the results reported by
Gustavson et al. (1974) in which coyotes were shown to
recondition themselves to the taste of rabbit flesh by
eating small amounts of the prey and waiting to see if they
became ill as a result.
This occurred when these animals
were given no alternative source of prey.
Coyotes kept
under tnore natural conditions and given an alternative
s.cu.rce of prey (Gustavson et al., 1976) went for several
weeks without showing any signs of aversion extinction.
One of the most remarkable abilities displayed by
·the fox squirrel was to be able to differentiate between
the peanut butter and the filbert nuts as to the illness
causing agent.
Brett et al. (1976) reported that the hawks
inspected their vomitus in which the black coat color was
apparent and thereafter avoided the black prey even
though both black and white coated prey had been consumed.
The mechanism through which the fox squirrels discriminated
between the two foods was apparently gustatory.
The fox squirrel gnaws on objects in it's environment
101
which results in wear of the incisor teeth.
The squirrels
use telephone cable as one of the objects to accomplish
this wear.
Since the animals do not feed on the cable,
but merely chew on it, one might ask how the conditioned
taste aversion could operate to prevent cable damage7
Lithium chloride is a deliquescent substance, that is, by
absorbing water vapor from the atmosphere, it will go into
solution when left stand in air at room temperature.
It
is very soluble in water (1.3 g dissolves in 1.0 ml of
cold water; J.T. Baker Chemical Co., 1978) and is,
therefore, also soluble in saliva.
The method of gnawing
utilized by the fox squirrel results in the interior of
the mouth coming into contact with the cable being gnawed.
The chemical would be brought into contact with the
interior of the ntouth and become soluble in a squirrels
saliva, resulting in a small dose of lithium chloride
being administered at each gr1awing session.
Repeated
small doses of this chemical of approximately 0.08 gram
could ultimately lead to conditioning against the taste
cues of the cable.
If a larger amount were absorbed (0.12
to 0.17 g) the conditioning could occur at the first
gnawing session.
The conditioning would result in
avoidance behavior directed toward any cable with the same
sensory cues.
The results of the field experiment show a
significant difference between protected and unprotected
cable in the amount of damage sustained.
I cannot prove
102
that conditioning or aversion have taken place in the field
study; however, the experiments conducted in the laboratory
suggest that this is possible.
If the animals reduce
damage in one area over another, some factor must be
affecting the result.
I submit that the difference is the
lithium chloride and that aversive conditioning is the
probable mechanism for the observed result.
Galef and Clark (1971) conditioned Norway rats
.
(Rattus norvegicus) to avoid a favored food by associating
that food with poison (lithium chloride).
The rats were
then offered a less favored food as an alternative food
source.
Rat pups born to members of this rat colony were
shown to avoid the food which was being avoided by tlie
adult rats.
These rat pups continued to avoid that food
-even when they were removed to a new
enc~~osure
and given
the same choice without the presence of the adults to guide
them.
In a later study (Galef and Clark, 1972) rat pups
were shown to avoid food which thelr parents avoided based
····-,-on
cues contained in the mother's milk.· These rat pups
.. ~-avoided the diet their parents were avoiding even though
--~:they-never-.observed
their parents feed:l.ng.
The rat pups
·were fed in a separate enclosure to avoid any possible cues
left by the parents' scent at the food dish.
Gustavson
et al. (1974) suggested that the training of coyote pups
by parents which had been averted from preying on a
specific animal could pass an aversion on ·to another
10.3
generation of coyotes which had never been conditioned.
The possibility exists that a fox squirrel which
chews on te1ephone cable could be passing the tendency
along to her young through her milk because of flavor
changes induced by ingestion of materials from the cable.
However, a young squirrel which ts raised by a mother
conditioned against cable chewing would have no such
tendency as her milk would be a "normal" flavor.
In
addition, a young squirrel which never observed the adult
squirrels gnawing on a cable could not learn the habit
through observational learni!lf.
Many such environmental
factors may contribute to the reasons why fox squirrels
gnaw· on telephone cable.
Some of these, as discussed
ab:ove! could be eliminated as possibilities through the
tech:nique of induced avoidance behavior.
I have no way of knowing which squirrel or squirrels
were responsible for the attacks in any particular site.
The distribution of the data collected at the beginning of
this study had indicated that the concentrations of damage
shift from year to year.
The observations in the field
indicated to me that particular individuals might be
responsible for the majority of cable damage in a
particular area.
If specific individuals are responsible
for cable damage, the loss of a single squirrel from a
given area would be significant.
The death of a cable
chewing individual and the dispersion of its young which
104
have learned to gnaw on cable through observation could
\
explain the observed shifts in damage concentrations.
The
Andasol and Costello-Colbath sites had the highest density
of squirrels and the least damage sustained during the
course of this study.
The majority of the damage occurred
· in the Murietta-Costello and Columbus sites which had
relatively small populations of squirrels.
However, these
two sites were also the most undisturbed of all the sites
except Costello-Colbath.
Also, a cable span located in one
area of many squirrel nests had damage points nearby,
whereas another span near a nest concentration had no
damage.
The limited nature of the data here does not prove
the above statements.
Further work is needed for
verification.
I have shown some evidence that lithium chloride can
condition the fox squirrel to avoid a specific food
substance and that the chemical affects the animalcs
physiology in the manner necessary to induce a taste
aversion.
I believe that I have demonstrated that the
incorporation into cable construction of a chemical agent
capable of initiating avoidance behavior through aversive
conditioning could serve to protect an aerial cable from
rodent attack.
If the chemical agent is capable of
causing illness in rodents and if that chemical has no
appreciable taste or smell the illness should be associated
with the object being chewed.
The avoidance behavior
--------
------
105
would then be directed toward the object which caused the
illness.
If
the rodent perceives the same sensory cues in
another object, that object would also be avoided.
The long-lived fox squirrel (Fouch, 1958; Hall and
Kelson, 1959; Ingles, 1965) could do a great amount of
damage to telephone cable in the six to seven years it has
been known to survive.
If fox squirrels were conditioned
against cable gnawing early in life, the amount of cable
damaged by this species would be reduced by a significant
margin over the lifetime of a chronic cable chewer.
The
illness and visual cues associated thereby should be enough
to prevent further attack.
In addition, the possibility
exists that this aversion could.be passed to succeeding
generations of squirrels, \Jhich could serve to eventually
eliminate the pt·oblem altogether.
106
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