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Use by Amphibiansand
eptiles in the Pacific
Robert E. Herrinyton2
In recent years, biologists have emphasized the importance of preserving habitats with high species diversity (Ehrlich and Ehrlich 1981).In
this context, habitats that play a critical role in the life cycle of a large
number of species should also be
considered for protection. However,
there is little information available
concerning habitat utilization by
many amphibian and reptile species,
and even less on the combined use of
a single habitat by both of these
groups (but see Scott and Campbell
1982).
Obtaining data on habitat use of
amphibians and reptiles is often hindered by the fact that habitat fidelity
is extremely variable for these
groups. Most studies have concerned
eastern species, but some generalizations have emerged. Small species
may be more or less restricted to a
single habitat (Ashton 1975, Barbour
et al. 1969, Fitch 1958, Gregory et al.
1987, and Rose 1982).Others routinely occupy two or more distinctly
different habitats over a single season. The latter group includes species
that migrate to reproduce and those
which use a separate habitat for hibernation and /or aestivation (Brown
and Parker 1976, Duvall et al. 1985).
'Paper presented at symposium, Management of Amphibians, Reptiles, and
Small Mammals in North America. (Flagstaff, AZ,July 19-21. 1988.)
2RobertE. Herrington is Assistant Professor of Biology, Georgia Southwestern College, Americus, GA 3 1709.
Abstract.-Field data and a review of available
literature were used to categorize the extent of talus
usage by individual herpeto&ml species. Five
categories were recognized that ranged from
species essentially restricted to talus slopes to those
that were only occasionally observed there. More
than 60%of the amphibian and reptile species that
occur in the states of Oregon and Washington were
found to utilize talus habitats. In addition to species
essentially restricted to talus slopes, the most
frequent use patterns were to moderate the effects
of adverse seasonal weather conditions and the use
of talus slopes for reproductive activities.
However, the importance of a habitat
to the continued survival of a population is not necessarily correlated
with the time that a species spends
within it. Providing reproductive
habitat, refugia from adverse
weather conditions, or protection
from predators can disproportionately influence the role that a particular habitat plays in the ecology of the
animals that use it.
Talus slopes are "unique habitats"
(Maser et al. 1979), that represent the
gradual accumulation of weathered
rock fragments (mostly basalt and
andesite) from a cliff face (Strahler
1981). Individual slopes are quite
variable in rock size, aspect and in
the amount and type of vegetation
present. These factors interact in
complex ways to provide a broad
range of thermal and moisture regimes that amphibians and reptiles
can select. This study examines the
use of talus slopes by amphibians
and reptiles and compares these
findings with non-talus areas.
Study Area and Methods
Herpetofauna associated with talus
slopes and adjacent non-talus areas
was determined by field observation
and a review of the literature
(Campbell et al. 1982). For the purpose of this investigation, talus habitats were those in which the substrate was predominantly weathered
rock fragments (typically with an as-
sociated cliff-face) and included a 10
meter wide band of transitional habitat. Non-talus habitats were those in
which the substrate was not as described above and were located a
minimum of 1 0 meters from a talus
area. Aquatic habitats were not specifically sampled; however, specimens observed under objects located
above the high water mark were included in the analysis.
Field work was conducted between August, 1981 and August,
1985. During this period, more than
100 days were spent in the Cascade
Mountains of southern Washington
and northern Oregon. Additional
surveys ranging from 2-6 days each,
were conducted in the North Cascades of Washington, the Coast
Range of southern Oregon, and the
Wallowa Mountains of northeastern
Oregon. A total of 183 individual talus slopes and adjacent non-talus areas were surveyed. Approximately
equal time was spent searching talus
and adjacent non-talus habitats. Talus slopes were considered to have
been altered by human activities if
there was evidence of extensive rock
or tree removal.
Searches were conducted by turning surface debris, raking through
leaf litter, and in the case of talus, by
digging in the upper layers of rock
with a potato rake. Data recorded for
most specimens included habitat
type, the activity the animal was engaged in when first observed (active
or inactive, surface or sub-surface,
foraging or involved in reproductive
activities), and a subjective evaluation of the individual's approximate
age (hatchling, juvenile, or adult).
The determination that an individual
was using talus to avoid unfavorable
weather conditions was based on the
season, prevailing weather conditions, the behavior exhibited by the
animal when uncovered, and the
depth at which the specimen was located.
These observations were summarized in an effort to categorize patterns of talus use. Voucher specimens
of most species have been deposited
in the vertebrate collection, Department of Zoology, Washington State
University. However, the majority of
specimens were identified in the field
and released at the site of capture.
Results and Discussion
Habitat Use
A total of four species of frogs were
observed in talus habitats (table I),
with a fifth species reported using
talus areas for feeding (table 2). A
single Hyla regilla and two Rana aurora were located under snow covered talus and were considered to
have been hibernating there. All frog
species were more numerous in nontalus areas and two species (Ramcascade and R. aurora) observed in nontalus areas were not recorded from
talus areas.
Salamanders were numerically
and taxonomically the most abundant amphibians encountered during
the study. The number of species recorded from talus and non-talus
habitats were 14 and 13, respectively
(table 1). However, species richness
is somewhat misleading, since more
than 90% of the observations of Plethodon elongatus, P. larselli, P. stormi,
and P. vandykei were from talus habitats. I consider these species to be
essentially restricted to forested talus
areas. This observation is supported
by the work of Stebbins and Rey-
nolds (1947) with P. elongatus, Nussbaum et al. (1983) with P. stomi and
P. vandykei, and Herrington and
Larsen (1985) with P. larselli. Five
additional species (Dicamptodon ensatus, P. dunni, P. vehiculum, Ensatina
eschscholtzi, and Batrachoseps wrighti)
were observed more frequently in
talus than in other habitats (table 1).
All the salamanders mentioned
above with the exception of Dicamptodon ensatus, are capable of completing their entire life cycle within talus
habitats. I observed portions of the
courtship sequences of Plethodon vehiculum and P. vandykei only on
damp talus. Many of these same species probably nest in deep recesses
within the talus. This is based on two
observations. The first is that given
the abundance of some salamander
species, very few nests have ever
been located (Hanlin et al. 1979,
Jones and Aubry 1985).This suggests
that nests are located in places generally inaccessible to investigators. The
slope and rock size associated with
talus fields generally precludes digging at depths > 50cm without the
talus caving in. Secondly, I found
small aggregations (1-3 individuals)
of P. larselli, P. vehiculum, and P.
dunni, that approached the size reported for hatchlings (Stebbins 1951,
Peacock and Nussbaum 1973, Herrington 1985) only in loose talus areas, following the first fall rains. This
is the time that recent hatchlings are
likely to to emerge from their nests.
Individuals uncovered from talus
in situations suggesting that they
were in winter dormancy included
Am bystoma gracile, A. macrodactylurn,
Dicamptodon ensatus, Rhyacotriton
olympicus, Plethodon dunni, P. larselli,
P. vehiculum, and Taricha gmnulosa.
Conversely, between June and August there was reduced rainfall and
elevated surface temperatures
throughout most of the study areas.
Because of this, surface activity by
salamanders was greatly restricted
and the majority of observations
(83%)were of individuals uncovered
from talus areas.
A total of 5 species of lizards were
observed or reported from talus
habitats (tables 1 and 2). Elgaria coerula was the most frequently observed
species and most individuals were
uncovered from the upper layers of
talus. Two behavioral patterns were
apparent. The first involved individuals uncovered before they had
emerged from nocturnal retreats and
the second was of individuals thermoregulating under surface talus.
Elgaria coerula is a live-bearing species and this behavior may be important to the developmental processes
taking place. Talus habitats have
been identified as oviposition sites
for Sceloporus occidentalis and Uta
sfansburiana (Maser et al. 1979) and
Elgaria multicarinata (Brodie et al.
1969).Elgaria coerula and E. multicarinata were uncovered from talus
slopes where they appeared to be hiberm ting .
Ten species of snakes were observed (table I ) and two additional
species reported from talus habitats
(table 2). Taken as group, snakes
were most frequently observed basking either on the surface or between
exposed rocks. Species that I considered to be entering or emerging from
hibernacula located within talus were
Crotalus viridis, Pituophis melanoleucus, Coluber constrictor, Thamnophis
elegans, T. ordinoides, T. sirtalis, Hypsiglena torquata, and Contia tenuis.
Both Hypsiglena torquata and Contia
tenuis were only observed in talus
habitats during the study, but they
are known to occupy a broader range
of habitats elsewhere (Cook 1960;
Diller and Wallace 1981).
Talus slopes play an important
role in the reproductive activities of
snakes. Brodie et al. (1969)reported
several individuals of Coluber constrictor, Diadophis punctatus, Contia
tenuis and Pituophis melanoleucus ovip s i ting within an exposed talus
slope in Benton Co., Oregon. I observed gravid females of Tharnnophis
sirtalis, T. ordinoides and Crotalus
viridis basking on talus slopes during
late summer. Whether these snakes
delivered their young at the talus
slopes is not known. However,
gravid C. viridis are known to remain
in the vicinity of their hibernacula to
produce young (R.Wallace, Department of Biological Sciences, University of Idaho, pers. comm.), and I uncovered 7 "yearling'f T, ordinoides
from an area of talus less than 2 m2,
where they appeared to be in hibernation. It was not possible to determine if these snakes had independently congregated there, or if they
represented a single litter born at the
talus slope, but the latter explanation
seems more plausible.
The importance of talus slopes in
the feeding ecology of snakes is unknown. The relative abundance of
garter snakes and salamanders on
talus slopes at certain times of the
year could lead to predator-prey interactions. This is supported by evidence palpated from the stomachs of
two Tharnnophis sirtalis and one T.
ordinoides captured on talus slopes.
Each of the 7'.sirtalis contained a
salamander (1 Plethodon dunni; 1 Ensatina eschscholtzi); the single T. ordinoides contained a large slug (Ariolimax sp.). While other interactions
were not observed, small mammals
often were observed in talus habitats.
Alterations to Talus Slopes
It became apparent after the initiation of this study, that a large number of the talus slopes being surveyed had been or were being altered by human activities. Habitat
modifications involved two not mutually exclusive alterations. The first
was the removal of rock from the
base of talus slopes to be used for
road construction raw materials (fig.
1). The second involved tree removal
(clearcutting) from the talus slopes.
I revisited talus slopes surveyed in
the early part of the project to determine the frequency and type of alteration. Of 183 talus slopes surveyed, 106 were altered; 76 had noticeable quantities of talus removed,
13 had been deforested, and 17 had
been altered by both events.
I was able to document few clear
species specific trends between altered and unaltered talus slopes (see
Conclusions). However, there were
differences in the number of individuals encountered. Unaltered
slopes represented 42% of the habitats surveyed but yielded 73%of the
total number of individuals. Because
there were differences in the amount
of search effort (time) expended surveying altered and unaltered talus
habitats, I did not statistically compare these results.
Conclusions
Figure 1. A comparison between the structure of an unaltered talus slope in winter (A) and a
slope that has had extensive rock removal for road building raw materials (B).
Talus slopes provide important habitat for a significant segment of the
herpetofauna of the Pacific Northwest. A total 37 of the 58 species of
amphibians and reptiles that occur
the states of Washington and Oregc
are documented from talus slopes.
Use of this resource by amphibians
and reptiles was quite variable, but
three important fa tterns emerged.
The first involves species essentially
restricted to talus habitats. Four species of plethodontid salamanders fit
this pattern (Plethodon larselli, P. vandykei, P. elongatus, and P. stomti).
The second category of talus use
consisted of species which use talus
slopes to avoid potentially lethal
temperature extremes. Nineteen species (10reptiles, 9 amphibians) were
included here. Several species of
snakes travel considerable distances
to congregate at communal hibernacula (Duvalk et al. 1985, Gregory and
Stewart 1975, and Brown and Parker
1976).This behavior conceivably
could put an entire population at risk
if the hibernacula were irreparably
a1tered.
A third use pattern of talus slopes
was for reproductive activities. In
addition to an egg-laying aggregation
of 5 species of reptiles reported by
Brodie et al. (1969), live-bearing r e p
tiles were frequently observed in therrnoregulatory behaviors on and
along the edge of talus slopes. The
importance in this behavior to completion of developmental processes
remains to be determined.
Each of these utilization patterns
is important to a particular segment
of the hergetofaunal community.
Whether or not the availability of
suitable talus slopes is a limiting factor for any of these species remains
unknown. However, talus slopes
typically make u p only a small portion of the available habitat. In the
Gifford Pinchot National Forest
(where a large part of this work was
conducted), Scharpf and Dobler
(1985) found talus slopes to occupy
less than 5% of the total land area,
most other areas have less.
The high frequency of altered talus slopes observed during this study
may pose a significant threat to the
long-term survival of many of the
amphibians and reptiles that use
them. Talus removal for road building materials and tree removal from
the slopes initiate complex changes
in the structure of the slope. Trees,
through leaf fall, provide a major input of nutrients to the slope, as well
as increasing the moisture retention
capabilities of the sub-surface talus.
Tree removal increases the solar radiation reaching the slope and this
results in the rapid loss of moisture
from the upper layers of talus. In a
study comparing the habitat selection
of P. larselli and P. vehiculum (Herrington and Larsen 1985),tree removal was implicated in rendering a
talus slope unsuitable for habitation
by P. larselli, but not for P. vehiculum.
Talus removal results in a major
shift of the slope towards its base.
This results in the extensive movement of both surface and deep layers
of talus. The immediate effect would
be to kill or injure many of the reptiles and amphibians inhabiting the
slope as well as destroy any nests located there. A long term consequence
of rock removal is that erosional
processes are increased. This results
in an increase in the amount of soil
present in the talus, and could conceivably close off access and fill in
areas formerly used as hibernacula.
Management Recommendations
Prior to altering a particular talus
slope, a survey should be conducted
to determine the presence of threatened, endangered, or otherwise sensitive species. Additionally, it should
be determined whether or not the
slope in question serves as a major
snake hibernaculum.
Tree removal from talus slopes
should be restricted and logging
practices should be modified to allow for leaving a sufficient border of
trees (20-30 m) along the margin of
talus slopes.
Current practices of removing talus for road building materials from
each slope encountered should be
discouraged. Selected talus areas
known not to contain threatened, endangered or sensitive species or to be
major snake hibernacula should be
utilized as a source of rock for construction activities.
One area that needs additional
study is the colonization and use by
amphibians and rep tiles of artificially
created talus areas. These would include areas such as the banks of road
cuts with riprap, and rock piles associated mining processes. Those
sampled during the study were
found to have a depauperate fauna
compared to natural talus areas and
the fauna consisted almost entirely of
species known to have broad habitat
tolerances. However, the possibility
remains that with adequate planning,
suitable areas could be constructed in
such a manner to benefit amphibians
and reptile faunas.
Acknowledgments
Portions of this study were funded
by the Washington Department of
Game, the Mazamas, the Society for
the Study of Amphibians and Rep
tiles, and Washington State University. Brian Miller, Chris Davitt, and
Linda Whittlesey assisted with field
work. Comments and suggesti.onsby
Stephen Corn, Patrick Gregory, and
Kieth Severson substantially improved this manuscript. Shelia Hines
typed the numerous drafts of this
manuscript. For all of this help, I am
exceedingly grateful.
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