Squirrels of the World

Ecology, Behavior, and Conservation 13

sual displays in any species of squirrel. As in many mam-
mals, chemical communication is a particularly important
means of passing along information. Most squirrels have
glands that produce chemicals (believed to be pheromones)
in their cheeks, back, and fl anks. Oral-nasal contact (often
termed greeting or kissing) is a common means of interact-
ing among the most social species, such as when individuals
approach each other and touch nose to cheek. Even in less
social species, the glands of the oral and cheek regions are
used to deposit scent-marks. Rubbing other parts of the
body and applying urine to structures and substrates also
convey data on occupancy and perhaps dominance, because
scent-marking increases with dominance in some species,
such as Sciurus niger.
The calls of the Sciuridae are quite variable, from high-
pitched single notes and prolonged squeals to low-pitched
“chucks” and guttural tones. Some nestlings produce ultra-
sonic calls, and at least some species of Sciurus are capable of
hearing in this range; however, the ultrasonic frequencies
have not received much attention. Many nocturnal species
of fl ying squirrel appear to be relatively silent. Studies by D.
T. Blumstein on the alarm calls of squirrels have served as
models for similar research in other taxa and have generated
and tested important hypotheses. For example, they have
shown that diurnality, and not sociality, is the most impor-
tant factor in the evolution of rodent alarm calls. They have
also begun to unravel the infl uence of physical and social
environments on vocalizations. The alarm calls of some

species of ground and tree squirrels appear to be relatively

simple and intuitively related to the acoustics of their habi-

tat; however, recent work demonstrates that calls by Gun-

nison’s prairie dogs (Cynomys gunnisoni) encode a great deal

of information. C. N. Slobodchikoff and his collaborators

show that the calls of this social species distinguish not only

t he t y pe of predator (terrest ria l versus aeria l)—a fi nding that

has been described for other marmotine ground squirrels—

but also unique characteristics of the potential predator, in-

cluding its color.

Social Behavior

The interspecifi c variation in social and mating systems

makes the Sciuridae excellent model organisms for the

s t udy of socia l evolut ion. Ea rly model s recog n i zed relat ively

asocial species (such as many of the chipmunks [Tamia s],

small-bodied ground squirrels, and tree squirrels) and

highly social species with overlapping generations of pri-

marily female relatives living together (such as many of the

marmots [Marmota], prairie dogs [Cynomys], African ground

squirrels [Xerus], and eastern gray squirrels [Sciurus carolin-

ensis]). The ability to achieve independence within the fi rst

year of life appears to be an important correlate of sociality;

species in which juveniles are able to reach adult size and

disperse by the time they are 1 year old are rarely social.

Sociality occurs primarily when female kin remain to form

kin clusters within local populations, and kin-diff erential

behaviors often take place within these female kin clusters.

A round-tailed ground squirrel (Xerospermophilus tereticaudus) with a rattlesnake. Photo courtesy Karen Munroe.