Made in United States of America
Reprinted frmn THE JouRNAL OF ';\'ILDLIFE 1L\.NAGEMENT Vol. 32, No. 1, January 1967 pp. 104-108 SNOWSHOE HARE PREFERENCE FOR SPOTTED CATSEAR FLOWERS IN WESTERN WASHINGTON BY :tvl.
A. RAnwAN AND D. L. CAMPBELL
PuRCHASED llY TilE FOREST SERVICE, U, S, DEPARTMENT OF AGRICULTURE, FOR OFFICIAL USE,
SNOWSHOE HARE PREFERENCE FOR SPOTTED CATSEAR
FLOWERS IN WESTERN WASHINGTON
M. A. RADWAN, Pacific Northwest Forest and Range Experiment Station,
D. L. CAMPBELL,
U.
U.
S. Forest Service, Olympia, Washington
S. Bureau of Sport Fisheries and Wildlife, Olympia, Washington
Abstract: Relative preference by snowshoe hares (Lepus americanus washingtonii) for leaves, flower
buds, and open flowers of spotted catsear ( H ypochoeris radicata) was studied in western Washington.
The hares demonstrated preference for open flowers, followed closely by flower buds. Leaves, alone
or in presence of open flowers or flower buds, were the least preferred part of the plant. Sugar content
was calculated on both fresh- and dry-weight bases, and advantages of the former method are dis­
cussed. Based on fresh weights, levels of glucose and fructose-the principal sugars of catsear-ap­
peared to be responsible for the observed order of preference, although other factors were not ruled out.
The snowshoe hare causes significant
damage to seedlings of Douglas fir (Pseu­
dotsuga menziesii) in the Pacific North­
west (Moore 1940:18, Munger 1943:55 ) . At
present, the most common control method
against the hare uses repellent formulations.
However, even the best repellent now avail­
able protects seedlings no longer than
through winter dormancy following treat­
ment (Besser and Welch 1959:168 ) . Better,
longer lasting repellents or perhaps new
control measures are needed.
Development of better control methods
requires a thorough knowledge of the
snowshoe hare, especially its habitat re­
quirements. During home range determina­
tion studies with radio-instrumented hares
in western Washington, the junior author
found spotted catsear to be one of this ani­
mal's preferred foods. Hares utilized the
plant all year but fed heavily and almost
exclusively on open flowers when they be­
came available. The experiments reported
in this paper are the result of subsequent
investigations to study the relative prefer­
ence exhibited by snowshoe hares for
leaves, flower buds, and open flowers of
the spotted catsear plant and to determine
the relationship between preference and
content or kind of sugar in different parts
of the plant.
104
MATERIALS AND METHODS
Catsear plants were collected from a
clearcut Douglas-fir area in Grays Harbor
County, Washington. The area of approxi­
mately 515 acres was logged in 1957-58
and planted to 2-year-old Douglas fir in
1960. Snowshoe hares severely damaged
many of the trees soon after they were
planted. Natural vegetation was varied
and abundant. Dominant species included
vine maple (Ace1· circinatum), salmon­
berry (Rubus spectabilis), western sword­
fern ( Polystichum munitum), and western
bracken ( Pteridium aquilinum). Catsear
occurred mainly in openings and under
bracken.
Three 14-acre sample plots, varying in
elevation and topography, were established
in hare-occupied habitat. Plant material for
preference and sugar determinations was
taken from each of the plots in June, 1966.
Preference Tests
Plants from the test plots were individ­
ually transplanted to plastic pots contain­
ing soil from the plant collection areas.
Immediately before the test, dead and un­
wanted parts were removed and plants
were trimmed to a uniform size, producing
three categories of plants for testing: ( 1 )
plants with leaves only, (2) plants with
HAnEs PREFER CATSEAR FLOWEHS
leaves and flower buds, and (3) plants with
leaves, flower buds, and open flowers. On
each plant, there was a minimum of 20 of
whatever plant parts were to be tested.
Nine plants, three from each category, were
randomly placed 3 ft apart in the center
of a 1-acre testing pen which contained 20
hares. The hares were allowed to feed on
the plants overnight in presence of natural
vegetation and commercial pelleted food.
At the end of the test, the plants were in­
dividually examined to determine the na­
ture and extent of hare feeding. Four tests,
7 days apart, were conducted.
Sugar Analysis
Samples of leaves, flower buds, and open
flowers were collected from each of the
plots. Leaf samples comprised only inter­
mediate, fully expanded leaves; bud and
open flower samples each included 1 inch
of the floral stem. Each plant part sample
was taken at random from 25 plants and
weighed approximately 100 g. Samples
were individually sealed in glass containers
and brought to the laboratory in a portable
cooler. Each sample of plant material was
then cut into small pieces and thoroughly
mixed.
Plant material was dried to constant
weight at 65 C to detennine moisture and
dry-matter contents. Determinations were
made on paired samples taken concurrently
with samples for sugar analysis.
Sugars were extracted from the fresh
plant tissue by adding hot alcohol at a final
concentration of 80 percent and extracting
in a Soxhlet apparatus for 12 hours. The
alcoholic solution was then made to volume
with the extracting solvent.
Portions of the alcohol extracts were con­
centrated on a water bath, clarified with
lead acetate, and subjected to sugar deter­
minations before and after hydrolysis ac­
cording to Hassid's eerie sulfate method
•
Radwan and Campbell
105
(1937) . Quantities of reducing and total
sugars and those of nonreducing sugars
were calculated as glucose and sucrose
equivalents, respectively.
The same alcoholic extracts were used
for separating sugars by paper chromatog­
raphy. Portions of these extracts were par­
titioned between ·water and chloroform to
remove lipids and chlorophyll. The aque­
ous phases were evaporated to dryness by
warm air jets, and residues were dissolved
in 1-ml amounts of distilled water. Result­
ing extracts were applied to Whatman No.
1 chromatography paper.
Descending one- and two-dimensional
chromatography was used (Block et al.
1958) . In the first method, chromatograms
were developed twice (multiple develop­
ment technique) \Vith n-butanol: pyridine:
water (6:4: 3 v/v/v) solvent. In the two­
dimensional method, the paper was first
developed in the short direction with liquid
phenol: water (4: 1 v/v) with 0.04 percent
8-hydroxyquinoline and then in the long
direction with the upper phase of n­
butanol: acetic acid:water (25: 6:25 v/v/v) .
Sugars on all dry chromatograms were
located with the aniline-diphenylamine­
phosphate color reagent (Block et al. 1958:
194) . Identity of the sugar spots was estab­
lished from their RF values and by chroma­
tography with reference compounds.
RESULTS AND DISCUSSION
Preference
Techniques available for evaluating ani­
mal preference of plants are not completely
without limitation. However, the method
used was chosen mainly because it more
closely approximated natural conditions
where hares are exposed to catsear plants
in association with other natural vegetation.
Leaves of catsear, alone or in presence
of open flowers and/or flower buds, were
the least preferred part of the catsear plant
106
Fig.
Journal of Wildlife Management, Vol. 32, No. 1, January 1968
1.
(Top) Potted catsear plants with leaves only (C2), leaves and flower buds (B3), and leaves, flower buds, and open
flowers (A2) just before the preference test.
(Bottom) The same plants at the end of the test.
(Table 1), Leaves were not utilized when
they were present on the same plant with
open flowers and flower buds (Fig. 1).
The hares, however, nipped off a few leaf
tips when open flowers were not present
on the plant and a little more when leaves
were the only plant part available. ·whole
leaves were eaten only after all the open
flowers and flower buds were consumed.
This pattern of use was consistently ob­
served when the plants were left in the
pen for an extra night beyond the regular
length of the test. Under these conditions,
leaves and remaining flower stalks were
totally consumed.
Although data in Table 1 indicate that
open flowers and flower buds of catsear
were equally preferred by the hares, dif­
ferences in preference between these two
plant parts were apparent during the tests.
Hares consumed open flowers first and
shifted to eating flower buds after open
flowers within their reach were consumed.
Also, on several occasions, hares were ob­
served standing on their hind feet seeking
the high open flowers, ignoring many
flower buds within their reach. On the
basis of these observations and data in
Table 1, it seems reasonable to conclude
that hares demonstrated a preference order
of open flowers, flower buds, and leaves.
Sugar Content
Sugar contents were calculated on both
the fresh- and dry-weight bases for com­
parative purposes (Table 2) . No variation
(within the limits of experimental error)
in amounts of either class of sugar oc­
cmTed among plants from the three sample
plots whether calculations were on the
HAREs PREFER CATSEAR FLOWERS
Table
1.
107
Radwan and Campbell
•
Percent consumption of leaves, flower buds, and open flowers of spotted cofseor by snowshoe hares.*
PLANT
CATEGORY
LEAYES
FLO,VER Buns
Area
Area
1
Leaves, flower buds, and flowers
Leaves and flower buds
Leaves only
0
0
lOt
2
3
0
5t
5t
0
8t
7t
92
90
OPEN FLO"'ERS
Area
2
3
1
2
3
84
100
96
94
100
85
95
* Tests were conducted overnight in a 1-acre pen with 20 hares, and all values are averages of four tests.
t Consumption limited to leaf tips.
fresh- or dry-weight basis. Furthermore,
both methods of calculation show that the
nonreducing sugar content was much lower
than that o£ the reducing sugars. The total
sugar content in the different parts of the
plant, therefore, was primarily due to the
reducing sugars present.
Calculations on a fresh-weight basis show
that leaves were lowest in the predominant
reducing sugars but highest of all parts in
the relatively minor :i1onreducing sugars.
Open flowers displayed sugar levels oppo­
site of those found in the leaves, and levels
of sugars in flower buds were intermediate.
Amounts of reducing sugars, therefore,
seemed to be a factor influencing prefer­
ence of hares for the different parts of the
catsear plant.
Calculations on a dry-weight basis show
that leaves Vi'ere intermediate in reducing
Table 2.
sugars and highest in nonreducing sugars.
Open flowers were highest in reducing
sugars and lowest in nonreducing sugars.
Flower buds were lowest in reducing sugars
and intermediate in nonreducing sugars.
Results of this method of calculation, there­
fore, demonstrated no correlation between
sugar and preference and suggested that
other factors were responsible.
The different data obtained by the two
methods of calculation resulted from varia­
tions in moisture content of different parts
of the plant. Average moisture contents of
samples from the three plots were 93.0 per­
cent, 86.3 percent, and 86.1 percent for
leaves, flower buds, and open flowers, re­
spectively. We believe that calculation on
a dry-weight basis, which allows accurate
comparisons after excluding this variable
moisture from all samples, is more appro­
priate in nutritional investigations. Here,
Sugar percentages of leaves, flower buds, and open flowers of spotted catsear.*
REDUCING SuaAnst
NoNREDUCING SuaAns:j:
ToTAL SuaARst
Area
Area
Area
PLANT
PART
1
2
3
1
2
3
Fresh-weight basis:
Leaves
Flower buds
Open flowers
0.71
1.40
2.17
0.75
1.27
2.17
0.74
1.24
2.14
0.07
0.04
0.01
0.11
0.03
0.01
0.09
0.01
0.01
10.50
10.23
15.53
10.66
9.36
15.64
10.63
9.36
15.64
1.04
0.09
O.o7
1.55
0.19
O.o7
1.30
0.10
0.05
Dry-weight basis:
Leaves
Flower buds
Open flowers
*Values are averages of two samples.
t Calculated as glucose equivalents.
:j: Calculated as sucrose equivalents.
2
3
0.79
1.44
2.18
0.86
1.30
2.18
0.84
1.26
2.15
11.60
10.32
15.60
12.29
9.46
15.77
12.00
9.46
15.69
108
]oumal of Wildlife Management, Vol. 32, No. 1, ]anuar!} 1968
absolute amounts of nutrients are required.
On the other hand, in preference studies
taste is usually suspected to be a factor.
Since, in some animals, including rabbits,
"water conveys a taste stimulus" (Kare
1966:12) and because taste is known to
vary vvith concentration, at least in man
and some animals (Amerine et al. 1965:
89), calculation on a fresh-weight basis
would seem to be the logical choice. This
method more realistically includes water
and expresses the chemical's concentration
in the plant as encountered by the animals
during the preference test (Alkon 1961:80).
Consequently, we adopted the fresh-weight
calculations in determining the reducing
sugar factor, which seemed to influence
preference ratings in this study.
Kinds of Sugar
Glucose and fructose were the only re­
ducing sugars present in leaves, flower
buds, and open flowers of catsear. In addi­
tion, examination of the chromatograms for
the nonreducing sugar fraction revealed a
trace of sucrose in flower buds and open
flowers and small amounts of sucrose and
three other higher unidentified sugars in
the leaves.
The principal sugars in catsear, therefore,
are the simple hexoses-glucose and fruc­
tose. Glucose (dextrose) ranks just behind
sucrose in sweetness, and fructose (lev­
ulose) is the sweetest of all sugars (Biester
et al. 1925:394). These two sugars are ex­
tremely important in the nutrition and
metabolism of animals (Fruton and Sim­
monds 1958:493). Such properties may
explain association of these reducing sugars
with preference by hares for the different
parts of catsear. However, perception of
sweetness has not been established for
hares, and some experiments with other
animals have failed to show correlation
between preference for food and its nutri­
tional value (Kare 1966:14). It is impos­
sible, therefore, to rule out factors other
than reducing sugars, such as proteins, fats,
tannins, etc. (Heady 1964:77), in explain­
ing the preference reactions of hares in this
investigation, even though other investiga­
tions have shown preference of other ani­
mals for sugars and synthetic sweet ma­
terials (Plice 1952:71, Carpenter 1956:143).
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Received for publication August 3, 1967.