Squirrels mate either once or twice a year and, following a
gestation period of three to six weeks, give birth to a number of offspring that varies by species. The young are
altricial, being born naked, toothless, and blind. In most species of squirrel, the female alone looks after the young, which are
weaned at six to ten weeks and become sexually mature by the end of their first year. In general, the ground-dwelling squirrel species are social, often living in well-developed colonies, while the tree-dwelling species are more solitary. while the flying squirrels tend to be
nocturnal—except for lactating flying squirrels and their young, which have a period of diurnality during the summer. During hot periods, squirrels have been documented to
sploot, or lay their stomachs down on cool surfaces. Squirrels, like other rodents, employ species-specific strategies to store food, buffering against periods of scarcity. In temperate regions, squirrels commonly cache nuts beneath leaf litter, inside hollow trees, or underground. However, in subtropical and humid environments, traditional caching can lead to mold growth, decomposition, or premature germination. To counteract these challenges, some squirrels, particularly in subtropical zones, hang nuts or mushrooms on tree branches. This behavior, believed to minimize fungal infections and reduce the risk of food loss, also inadvertently aids certain trees, like
Cyclobalanopsis, in expanding their range, with forgotten or dislodged nuts sprouting in new locations, influencing forest ecology. Two species of flying squirrel, the
particolored flying squirrel and
Hainan flying squirrel aid such cacheing by carving grooves into the nuts to fix the nuts tightly between small intersecting twigs, akin to the mortise-tenon joint in carpentry.
Feeding ,
Tanzania in the
Seurasaari island in
Helsinki,
Finland. The tame red squirrels on that island have become accustomed to humans thanks to their long-term feeding. seeds. Because squirrels cannot digest
cellulose, they must rely on foods rich in
protein,
carbohydrates, and
fats. In
temperate regions, early spring is the hardest time of year for squirrels because the nuts they
buried are beginning to sprout (and thus are no longer available to eat), while many of the usual food sources are not yet available. During these times, squirrels rely heavily on tree buds. Squirrels, being primarily
herbivores, eat a wide variety of plants, as well as
nuts,
seeds,
conifer cones,
fruits,
fungi, and green
vegetation. Some squirrels, however, also consume meat, especially when faced with hunger. Squirrels have been known to eat small
birds, young
snakes, and smaller rodents, as well as
bird eggs and
insects. Some
tropical squirrel species have shifted almost entirely to a diet of insects. Squirrels, like
pigeons,
feral cats, and other fauna, are
synanthropes, in that they benefit and thrive from their interaction in human environments. This gradual process of successful interaction is called synurbanization, wherein squirrels lose their inherent fear of humans in an
urban environment. When squirrels were almost completely eradicated during the
Industrial Revolution in
New York, they were later re-introduced to "entertain and remind" humans of nature. The squirrel blended into the urban environment so efficiently that when synanthropic behavior stops (e.g. people do not leave trash outside during particularly cold winters), they can become aggressive in their search for food. Aggression and predatory behavior has been observed in various species of ground squirrels, in particular the
thirteen-lined ground squirrel. For example, Bernard Bailey, a scientist in the 1920s, observed a thirteen-lined ground squirrel preying upon a young
chicken. Wistrand reported seeing this same species eating a freshly killed
snake. Sometimes squirrels prey on an atypical animal: a pack of black squirrels in 2005 killed and ate a large stray
dog in
Lazo, Russia. Squirrel attacks on humans are exceedingly rare. Whitaker examined the stomachs of 139 thirteen-lined ground squirrels and found bird flesh in four of the specimens and the remains of a short-tailed
shrew in one; Bradley, examining the stomachs of
white-tailed antelope squirrels, found at least 10% of his 609 specimens' stomachs contained some type of vertebrate, mostly
lizards and rodents. Morgart observed a white-tailed antelope squirrel capturing and eating a
silky pocket mouse. == Taxonomy ==