Squirrels of the World

Sciurus nayaritensis 59

conservation: IUCN status—least concern. Population
trend—stable. Japan’s Red Data Book lists Sciurus lis as a lo-
cally threatened population for populations in the Chugoku
and Kyushu districts.

habitat: Japanese squirrels are found in lowland to subal-
pine primary and secondary pine (Pinus) and mixed forests,
and they can also be found in suburban forests.

natural history: This species is diurnal. Japanese squir-
rels are active throughout the year and can often be seen
foraging on the ground or in the canopy. A group of males
follows the estrous female on her single day of receptivity
during a breeding season. Breeding occurs in two pulses:
February–March and May–June. After a gestation of 39–40
days, a litter of two to six young are born in a leaf nest, den
cavity, or burrow. The young are weaned within a few
weeks of exiting the nest and disperse from their natal areas
soon afterward. Adults are solitary, but occasionally they
have been observed to nest with other adults, especially in
winter. Male home ranges are between 4 and 30 ha, whereas
female home ranges are from 4 to 17 ha; overlap between
individuals is modest. Home ranges expand in heavily frag-
mented environments, because individuals must incorpo-
rate poor-quality marginal habitat. Japanese squirrels are
primarily herbivores, feeding on seeds, buds, fl owers, and
fruits, particularly those of trees. Insects and epigeous
(aboveground) fungi are also consumed when available. S. lis
scatter-hoards thick-shelled nonperishable foods (such as

walnuts) against winter food shortages. Annual mortality

has been estimated at 63 percent. Predators include martens

(Martes), foxes, domestic cats, domestic dogs, and a variety

of raptors and crows. Although S. lis was hunted in the past,

this has been illegal since 1994. Habitat loss, habitat frag-

mentation, and forest degradation due to disease are major

challenges for their conservation.

general references: Kataoka and Tamura 2005; Tamura

2004; Tamura and Hayashi 2007, 2008.

Sciurus nayaritensis (J. A. Allen, 1890)

Mexican Fox Squirrel

description: S. nayaritensis has a grizzled brown dorsum

with a yellow to rufous venter, and a charcoal tail frosted

with white. Two molts occur each year; the winter pelage is

more rufous, and the scrotum is often ringed with white.

size: Female—HB 259.1 mm; T 254.5 mm; Mass 667g.

Male—HB 248.2 mm; T 245.8 mm; Mass 736 g.

distribution: This species is found in the Chiricahua

Mountains in extreme southeastern Arizona (USA) and

south along the Sierra Madre Occidental into Jalisco

(México).

Sciurus lis. Photo courtesy Mikio Okubo, Sciurus lis of Nagano
Pre. Japan.