60 Sciurus nayaritensisgeographic variation: Three subspecies are recognized.
S. n. nayaritensis—southern portion of the range (México).
This is a smaller and more yellow subspecies.
S. n. apache—northern and middle portion of the range
(México). This form is intermediate in size and
coloration.
S. n. chiricahuae—Chiricahua Mountains of southeastern
Arizona (USA). An endemic form, it is characterized by a
more reddish coloration throughout the dorsal pelage
and venter.
conservation: IUCN status—least concern. Population
trend—no information. S. n. chiricahuae is a species of spe-
cial concern in the USA.
habitat: Mexican fox squirrels are found in forests, rang-
ing from low-elevation (> 1500 m) Madrean forests with a
mixture of pine (Pinus) and oak (Quercus) to higher-elevation
(< 2700 m) mixed conifer forests. Riparian areas with large
cottonwoods (Populus) and sycamores (Platanus) often har-
bor the highest densities of these squirrels.
natural history: This species is diurnal. The ecology of
Mexican fox squirrels is poorly known, although densities
are often low in the open arid forests that are inhabited by
this species. S. nayaritensis typically produces a single small
litter of one or two young in late spring or summer, after a
short day-long estrus in spring or early summer (February–
July), when multiple males pursue females. Males possess
scrotal testes in winter through summer; the testes are
withdrawn into the abdominal cavity during the remaining
months. Mexican squirrels nest almost exclusively in dreys
composed of sticks and leaves within the forest canopy;
cavities within large-diameter trees are occasionally used
by each sex and may be favored by nursing females. Com-
munal nesting is known. S. nayaritensis does not hibernate.
Home ranges of males average 35 ha, whereas females oc-
cupy 15 ha on average. Males maximize their overlap with
females, especially during the breeding season. Large rap-
tors, canids, felids, procyonids, and snakes are probably
this species’ major predators. Mexican fox squirrels are no-
tably silent and appear to prefer to seek cover and remain
motionless unless they are startled; then they will bark and
“chuck” from elevated locations. S. nayaritensis forages ex-
tensively on the ground and in the forest canopy for tree
seeds and fl owers, in addition to fungi. Seeds from the
cones of pines (Pinus), Douglas fi rs (Pseudotsuga menziesii),
and true fi rs (Abies) are consumed by removing individual
cone scales to excise the seed. Acorns and walnuts are also
eaten when available, along with a variety of other tree
seeds. In addition, hypogeous (underground) and occasion-
ally epigeous (aboveground) fungi, as well as insects, are
consumed by this opportunistic feeder. Mexican fox squir-
rels occasionally cache large storable seeds by scatter-
hoarding them in leaf litter and topsoil. Mexican fox squir-
rels are hunted for food and sport throughout their range.
Due to the low human population densities within the
range of this species, S. nayaritensis is of little economic
value or detriment.general references: Best 1995d; D. E. Brown 1984; Hoff -
meister 1986; Kneeland et al. 1995; Koprowski and Corse
2001, 2005; Pasch and Koprowski 2006a, 2006b; Yensen and
Valdés-Alarcón 1999.Sciurus niger (Linnaeus, 1758)
Eastern Fox Squirreldescription: The dorsal pelage of eastern fox squirrels is
variable. S. niger from the western and northern portions of
the range are grizzled with a suff usion of buff to orange; the
venter is white to cinnamon, but usually rufous. In the
southeastern USA, the dorsum is grizzled buff to gray to
agouti to black, with a white or cream nose, ears, and feet
and a black crown and nape; the venter is white to tan to
rust. Fox squirrels in the northeastern coastal portion of the
range are silvery gray washed with buff to a reddish tone on
the hips, feet, and head; the tail is pale gray; the venter is
white to pale gray, sometimes cinnamon. Melanism is com-
mon, especially in the south.Sciurus nayaritensis. Photo courtesy Bruce D. Taubert.