Transcript A Comparison of Abert squirrels, pine squirrels and fox

A Comparison of Abert
squirrels, pine squirrels and
fox squirrels with respect to
life in the cold
by
Justina Thorsen
2006
Winter Ecology – Spring 2006
Mountain Research Station – University of Colorado, Boulder
Topic under Consideration
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Abert, fox and pine squirrels have overlapping
ranges in Boulder Mountain Parks (BMP).
What are their different adaptations to the cold
winters on the Colorado Front Range?
The Tree Squirrels
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Sciurus = derived from Greek terms “shadow”
and “tail”
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Tamias = food caching
Bushy tails for: balance, communication and
Tbody regulation
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Thus, an animal who sits in the shadow of it’s tail (Gurnell
1987; MacClintock 1970)
Tails often approach 1/3 of body length
Hindfeet with 5 digits, forefeet with 4 digits
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May be furry in winter (Gurnell 1987)
Three Species Considered
Tamiasciurus
hudsonicus
Sciurus aberti
Sciurus niger
Where Are They?
Distribution of the Abert
squirrel
Where are They?
Distribution of the Fox Squirrel
Where are They?
Distribution of the pine squirrel
Nest Types
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Dreys: twig and leaf nests built in trees
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Winter dreys are more elaborate than summer ones & must
withstand inclement weather
Winter dreys tend to be circular; summer dreys saucer shaped
Dens: holes or cavities in tree trunks
Holes: underground or in rock
(Gurnell 1987)
Squirrel in it’s drey
Body Size and Bergman’s Rule
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In order of increasing size: pine, abert, fox
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Pine squirrels are smallest N. American tree
squirrel
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Occupy the coldest, most northern habitats in N. America and the highest
altitudes in Colorado
Fox squirrels are largest N. American tree squirrel
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Occupy the lowest altitudes in Colorado
Coat Color
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Abert squirrels of Colorado tend to be
melanistic
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Farentinos (1971) estimated 56.7% melanism
Pine squirrels are ashy gray with white
undersides
Fox squirrels are peanut colored with rusty
undersides
Is Black Beneficial?
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Golightly and Ohmart (1978) found that:
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Sun basking is common among Abert squirrels on
winter afternoons
Sun basking resulted in increased TBody
Basking squirrels had higher TBody than inactive
and nesting squirrels
Food Utilization
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Fox and pine squirrels are food generalists and
opportunistic eaters
Abert’s are food specialists and are
ecologically dependent upon Ponderosa pines
The primary food for all squirrels is tree seeds
and fruits
Secondary foods: berries, mushrooms and
other plant matter
Selective herbivory of Abert
squirrels
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Diet consists almost
entirely of ponderosa
pine tissues and other
closely associated
species (Snyder 1998, States and
Wettstein 1998)
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Abert squirrels eat
mycorrhizal fungi in the
summer months and
inner bark during winter
months (States and Wettstein
1998)
Food Caching of Pine Squirrels
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Pine squirrels establish middens which they
guard defensively
They cut and cache green cones in late summer
to ripen and provide winter food sources
(MacClintock 1970)
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Middens often have underground networks of
tunnels and nest cavities
Fall Gluttony of Fox Squirrels
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Fox squirrels prepare for the unpredictability
and scarcity of food resources during winter by
overeating in the fall (Steel and Koprowski 2001)
Fox squirrels may scatterhoard food
Levels and Patterns of Activity
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Inclement weather reduces activity, although
active squirrels may be seen in severe weather
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Wind and rain significantly reduce Tbody (Golightly and
Ohmart 1978)
Fresh snow severely restricts movements (Golightly and
Ohmart 1978)
Pine squirrels become subnivean and subterranean when
Tair is very low (Gurnell 1987)
Summary of Adaptations
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Aberts:
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Pine Squirrels:
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Behavioral – sun basking
Morphological – ear tufts, black coat
Physiological – utilization of inner bark
Behavioral – middens, territorial
Fox Squirrels:
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Behavioral – fall gluttony, scatterhoarding
Morphological/Physiological - BAT
Conclusions
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The three species of tree squirrels each exhibit
unique sets of adaptations to life in the cold.
All three species experience similar
environmental pressures where their ranges
overlap (on the Front Range of BMP)
All three species exhibit a degree of inhibition
from inclement weather (including: wind, rain, fresh snow, low
Tair)
Selected References and Literature
Cited
Armstrong, D.M. 1987. Rocky Mountain Mammals, revised edition. Boulder,
Colorado: Colorado Associated University Press. 223 pp
Farentinos, R.C. 1971. Social dominance and mating activity in the tassel-eared squirrel
(Sciurus aberti ferrus). Unpublished. PhD Thesis for the University of Colorado, Boulder. 73
pp.
Golightly, RT Jr. and RD Ohmart. 1978. Heterothermy in free ranging Abert’s squirrels (Sciurus
aberti). Ecology, 59(5): 897-909.
Gurnell, J. 1987. The Natural History of Squirrels. New York, New York: Facts on File
Publications. 201 pp.
Hamilton, WJ III and F Heppner. 1967. Radiant solar energy and the function of black
homeotherm pigmentation: an hypothesis. Science, 155: 196-197.
Keith, JO. 1965. The Abert squirrel and its dependence on Ponderosa pine. Ecology, 46: 150-163.
MacClintock, D. 1970. Squirrels of North America. New York, New York: Van Nostrand Reinhold
Company. 184 pp.
Larson, MM and GH Schubert. 1970. Cone crops of ponderosa pine in central Arizona including
the influence of Abert squirrels. USDA Forest Service Research Paper RM-58, Rocky Mtn.
Forest and Range Experiment Station, Ft. Collins Colorado. Pp. 15.
Marchand, PJ. 1987. Life in the Cold. Hanover: University Press of New England. 304 pp.
Snyder, M.A. 1998. Abert’s squirrels (Sciurus aberti) in Ponderosa pine (Pinus
ponderosa) forests: directional selection, diversifying selection. In: Steel J.F. and D.A. Zegers
(eds). Ecology and Evolutionary Biology of Tree Squirrels. 6th Special Publication. VA:
Virginia Museum of Natural History. p 195-201.
States J.S. and P.J. Wettstein. 1998. Food habits and evolutionary relationships of the tassel-eared
squirrel (Sciurus aberti). In: Steel J.F. and D.A. Zegers (eds). Ecology and Evolutionary
Biology of Tree Squirrels. 6th Special Publication. VA: Virginia Museum of Natural History. p
185-194.
Steel, MA and JL Koprowski. 2001. North American Tree Squirrels. Washington: Smithsonian
Institute Press. 201pp.