After some experience, a squirrel can open a nut in a few seconds. Seeds of conifers are eaten by squirrels that inhabit coniferous forests. Mushrooms, insects, birds' eggs, and small birds may also be taken. Individuals there showed great selectivity in use of trees for harvesting phloem, returning repeatedly to the same tree during a season and even from year to year. Nonetheless, feeding trees could recover from such activity in association with shifting local squirrel densities.
Males generally have larger home ranges than do females.
In the latter species, home ranges of males were found to overlap extensively with one another and with the ranges of females, but the female ranges did not overlap each other. Tree squirrels generally are not gregarious, but during the breeding season males may congregate on the home range of a female in estrus and fight one another for the right to mate. After mating the pairs separate. In the Northern Hemisphere mating occurs over an extensive part of the year, but there are usually peaks in winter and from late spring to early summer. In most species that have been investigated, adult females produce two litters each year.