Squirrels of the World

Sciurus colliaei 47

each year. The young emerge from the nest after 7–8 weeks
and are weaned beginning at 10 weeks. Adult size is
reached by 8–9 months of age. Most individuals do not re-
produce until at least their yearling year; precocious breed-
ing at 5.5 months by females is known when there is a su-
perabundance of food. Natal dispersal occurs soon after
weaning, with males leaving their natal area and some fe-
males remaining to form matrilines. Groups of related fe-
males and, occasionally, unrelated males will nest together
each night, often in tree cavities. The nest sites are aggres-
sively defended from a nongroup member attempting to
enter. Scent-marking with cheek glands is used to mark
trees, and these glands are smelled when individuals greet
each other. Traditional scent-marking sites are found in
protected areas, such as under low branches or on the un-
derside of a slanted tree trunk; primarily males gnaw the
location and then wipe their cheeks back and forth to de-
posit scent, and sometimes they urinate to scent-mark.
Eastern gray squirrels feed heavily on tree seeds, but
they also eat fruits, shoots, fl owers, fungi, and occasionally
animal matter (such as insects, bird eggs, and nestlings). A
conspicuous behavior is the annua l scatter-hoarding of hard
low-perishability nuts and acorns each fall to serve as the
winter food store. The squirrels collect tree seeds near the
parent tree, disperse to greater distances, and bury them
just under the surface. These behaviors all serve to decrease
the loss of this critica l food source to seed predators. To pre-
vent white oak–group acorns from germinating once buried,
eastern gray squirrels excise the embryo to ensure that the
seed’s nutrients remain available until recovered. Caches

are recovered using a combination of spatial memory and

olfactory cues. Reproduction is strongly tied to hard mast

production; litter size and the prevalence of lactation de-

crease in poor food years. Overlap in home ranges is consid-

erable, but females often defend exclusive-use cores, espe-

cia l ly during lactat ion. Home ra nges va r y from 0.5 ha to 20.5

ha, are larger in males, and decrease with density and with

decreasing habitat fragment size. First-year survivorship is

only about 25 percent, but then it increases to more than 50

percent throughout adult life. Record longevity in the fi eld

for males is more than 9.0 years, for females 12.5 years, and

as great as 20 years in captivity. Predators of S. carolinensis

are numerous and include mustelids, procyonids, felids, ca-

nids, raptors, and snakes. Alarm calls are a series of me-

dium-pitched barks, often followed by long high-pitched

whines.

Eastern gray squirrels are frequently valued in parks and

cities, and they are also hunted as game animals. S. carolin-

ensis is considered a pest in orchards, gardens, agricultural

fi elds, and forest plots. Having been introduced to England,

this species continues to spread with deleterious conse-

quences: the stripping of bark (which kills trees), and the

rapid displacement of native Eurasian red squirrels (Sciurus

vulgaris). In the state of Washington (USA), introductions of

this species are believed to play a role in the reduction of

western gray squirrels (Sciurus griseus). Habitat loss and frag-

mentation remain the most signifi cant threats to eastern

gray squirrels in their native range.

general references: Bertolino 2009; Hopewell and

Leaver 2008; Hopewell et al. 2008; Koprowski 1994a, 1996;

Steele and Koprowski 2001; Steele, Manierre, et al. 2006;

Wauters, Tosi, et al. 2002.

Sciurus colliaei (Richardson, 1839)

Collie’s Squirrel

description: Collie’s squirrel is a gray-colored squirrel of

moderate size, and it is sometimes referred to as a “gray

squirrel” in México, along with S. aureogaster. However, the

dorsum is usually dark, grizzled gray with a yellowish wash

that continues to the base of the tail. The sides are light gray.

The venter is usually white, but it can sometimes be light

orange. The dorsal surface of the tail, other than the base,

is black with a white wash. The ventral surface of the tail is

grizzled gray, or dark gray and yellow, with white along its

edges. This species has two upper premolars, except in the

northern parts of its range, where one is missing in some

individuals.

Sciurus carolinenesis, black morph. Photo courtesy Laura
Finnegan.