14 Ecology, Behavior, and ConservationCommunal nesting, however, is among the most common
behaviors documented not only within highly social spe-
cies, but also in ground squirrels, fl ying squirrels, and tree
squirrels. Although sociality has been well described for
many temperate-zone squirrels, nocturnal fl ying squirrels
and many tropical tree and ground squirrels remain rela-
tively unstudied; most likely they will provide excellent
tests of existing hypotheses on the evolution of sociality.
Kin Recognition, Kin Selection, Alarm Calling,
and Infanticide
The overlapping generations of kin within kin clusters pro-
vide unique opportunities for the study of kin recognition
and kin selection. The importance of nepotistic behaviors
in nonhuman systems was exemplifi ed by classic work on
the ground squirrels (Urocitellus beldingi, U. columbianus, Xe-
rospermophilus tereticaudus, and Cynomys ludovicianus). More
recent studies suggest that such forms of conduct might also
exist in the marmots, tree squirrels, and fl ying squirrels, es-
pecially with regard to communal nesting in challenging
winter climates. Kinship infl uences many actions by ground
squirrels, including nesting associations, alarm calling, and
the distribution of amicable and agonistic behaviors. For
example, Belding’s ground squirrels with relatives nearby
are more likely to call and risk detection by a predator. De-
tailed studies on Belding’s ground squirrels and golden-
mantled ground squirrels (Callospermophilus lateralis) dem-
onstrate that recognition of close and distant relatives
occurs at least in part through olfactory cues; however, dif-
ferential treatment of individuals based on kinship only oc-
curs in U. beldingi, whereas C. lateralis treat unrelated and re-
lated individuals similarly and agonistically. Studies to assess
the costs and benefi ts of kin recognition in a number of other
species are likely to produce similarly fruitful results.
A potential cost of living in such groups is the likelihood
of negative actions, such as infanticide. Infanticide has been
reported in a number of ground squirrels, and it is probably
more common than has been observed. Initial reports sug-
gested that it was an aberration; however, recent studies in
the marmotines (Cynomys and Urocitellus beldingi) indicate
that this behavior is most likely a strategy of females. In
Belding’s ground squirrels, infanticide appears to be a means
of increasing genetic benefi ts by eliminating nonrelatives.
In black-tailed prairie dogs, lactating females direct their in-
fanticidal eff orts at the off spring of related lactating females,
and the benefi ts appear to be increased immediate nutrition
(from eating the babies that are killed), reduced competition
for resources, and potential cooperation in other duties—
defending territory, watching for predators, and maintain-
ing burrows—from marauded females (i.e., those whose
off spring have been killed, and who thus no longer have
infants to care for). Again, kinship seems to play an impor-
tant role.Foraging Ecology
Seed Predation and Herbivory
Although it would not be incorrect to suggest that squirrels
eat everything, it would be quite misleading. Indeed, most
species are opportunistic and typically include a variety of
plant as well as animal material in their diets. Such diet
breadth varies across and within taxa, and even across geog-
raphy or season for the same species. Some species, how-
ever, are dietary specialists, such as the woolly fl ying squir-
rel (Eupetauras cinereus) from Pakistan, India, and Tibet,
which feeds almost entirely on conifer needles, and the
shrew-faced squirrel (Rhinosciurus laticaudatus) from the Ma-
lay Peninsula, which specializes on ants and termites. Oth-
ers are bark gleaners (pygmy squirrels: Nannosciurus, Exilis-
ciurus, Myosciurus, and Sciurillus), and at least a few species of
Tamiops and Funambulus are reported to feed on nectar and,
in the process, may serve as pollinators. Most squirrels are
also known to include animal material in their diets: arthro-
pods, bird eggs, baby birds, adult birds or mammals, and
even conspecifi cs. Such carnivorous behavior and cannibal-
ism, however, is usually restricted to periods of food short-
ages. Limiting nutrients (i.e., those that are less readily ob-
tained, such as calcium and sodium) are also sought from
various sources, such as hypogeous fungi, antlers, and bone.
Despite these specializations, many generalities exist.
Tree squirrels, for example, are primarily granivores or fru-
givores, feeding mostly on seeds, nuts, and fruits. But within
this general context many species show remarkable special-
izations, depending on the biomes or forest types in which
they are found. In conifer forests, for example, tree squirrels
will often concentrate on the seeds from pines, spruce, fi r,
and other evergreens. They do this by systematically strip-
ping the bracts off of cones to get to the seeds at the base of
the bracts, thereby acting predominantly (but not always) as
seed predators in these forests. Many species have been
shown to systematically remove, eat, and larder-hoard the
entire cone crops of conifers.
Squirrels are highly selective with regard to feeding ef-
fi ciency in these forests. For example, one of us has shown
that fox squirrels (Sciurus niger) will systematically sample
one or a few cones from most of the longleaf pines (Pinus
palustris) within their home range and then systematically
select the most profi table trees in which to concentrate their
feeding activity. Similar patterns of cone selection have
been reported in other tree squirrels that reside predomi-
nantly in conifer forests. Such patterns of selection often
result in those trees that invest the most in female cone pro-
duction experiencing the highest rates of seed predation. In