Callospermophilus madrensis 257habitat: C. lateralis occupies a wide range of habitats (usu-
ally at elevations between 1220 and 3960 m), ranging from
sagebrush, chaparral, and pinyon communities to above the
alpine tundra. It also occupies open mountain meadows and
rocky slopes, and it will frequently colonize burned and tim-
bered areas; most areas of occupation have a signifi cant rock
component. The golden-mantled ground squirrel is often as-
sociated with stands of pine (Pinus contorta, P. fl exilis, and P.
ponderosa), spruce (Picea engelmannii), Douglas fi r (Pseudotsuga
menziesii), and quaking aspen (Populus tremuloides).
natural history: Classifi ed as an omnivore, C. lateralis is
opportunistic in its feeding habits, but it is highly granivo-
rous in the late summer and autumn, when the seeds of co-
nifers and oak acorns are available. It is known to cache
seeds, but details on this behavior are not available. Its con-
sumption of seeds may deter forest regeneration in some
areas. These squirrels also feed on a variety of shrub and
herb species, and they consume several kinds of animal ma-
terial, including insects, bird eggs, young birds, lizards, mam-
mals, and roadkilled conspecifi cs. In an experimental situa-
tion, C. lateralis has been shown to forage selectively on
artifi cial diets of polyunsaturated fats, which are readily
found in plants, are not produced by mammals, and are
critical for hibernation.
Golden-mantled ground squirrels excavate burrows that
are used for escaping predators, nesting, and storing food.
Burrows, which are up to 90 cm deep and 183 cm long, are
found near rocks, stumps, and logs; sometimes they are in
logs, stumps, and rock crevices. Burrows can be simple or
complex, but frequently they are more complex than those
of Tamias minimus; the burrows often have two or more en-
trances, usually oriented to the southwest. The length of
hibernation varies with temperature, altitude, and snow
depth, but it usually begins between late August and early
November and ceases between late March and early May.
Experimental restriction of caloric intake prior to hiberna-
tion delays the onset of hibernation, but apparently this has
no eff ect on the length of the torpor bouts; it results in a loss
of fat-free mass but not lipid mass. In the autumn, this spe-
cies undergoes fi ve to six periodic bouts of torpor, in which
body temperature steadily decreases and the length of each
torpor event increases, until the animal enters winter hiber-
nation. C. lateralis is able to prevent the pulmonary surfac-
tant secretion that typically occurs in most mammals when
exposed to fl uctuations in body temperature. The secretory
and regulatory pathways involved in this squirrel’s secre-
tion of surfactants are insensitive to thermal changes, and
its cells are able to survive at 0°C–5°C, suggesting an adapta-
tion that facilitates hibernation. During hibernation the dia-
phragm muscle becomes hypertrophied and shows greater
oxidative capacity; both changes are probably adaptations
that enhance gas exchange during torpor. Hibernation is
also aided by a suite of other physiological traits: for exam-
ple, the ability to control breathing, ventilation, and respira-
tory chemosensitivity; an unusually high level of plasticity
in the skeletal muscles; and the profi les, expression, and ac-
tivity of specifi c muscle enzymes.
Breeding begins soon after emergence, although some
females may not become reproductively active until a few
weeks after emergence. Gestation is estimated to range be-
tween 26 and 33 days, and litter sizes average fi ve (but are
lower at higher elevations). The young weigh about 6 g at
birth, are weaned after 35 days, and are the last to enter hi-
bernation. The golden-mantled ground squirrel has been
reported to live for up to 7 years in the wild. The animals are
generally silent, but they do rely on high-pitched alarm calls
and tail waving when threatened; in experimental situa-
tions they have been shown to learn to associate novel
sounds with the presence of a potential predator. This spe-
cies is prey for at least four species of carnivorous mammals
and two raptor species. Ectoparasites associated with C.
lateralis include 11 species of fl eas, 2 ticks, and 3 sandfl ies. Its
internal parasites consist of at least 7 species of 5 genera of
protozoans and 1 nematode species. The golden-mantled
ground squirrel also is a frequent host of Yersinia pestis, the
bacterium responsible for sylvatic (bubonic) plague. C. late-
ralis fossils are reported from the late Pleistocene; some de-
posits suggest that in the past, this species’ range may have
extended 260 km farther south, and to much lower eleva-
tions, than it does today.general references: Anthony 1928; Bartels and Thomp-
son 1993; Bihr and Smith 1998; Frank 1994; A. W. Linzey and
Hammerson 2008d; J. A. MacDonald and Storey 2002, 2004;
Ormond et al. 2003; Pulawa and Florant 2000; Rourke et al.
2004; Shriner 1999; Staples and Hochachka 1998; Zimmer
and Milsom 2001, 2002.Callospermophilus madrensis
(Merriam, 1901)
Sierra Madre Ground Squirreldescription: Although similar in color to its sister species
C. lateralis, C. madrensis is duller in its coloration, with
shorter and more faded dark stripes, and longer white
stripes. It also has a smaller body size and a shorter tail. The
skull is narrower, and the brain case is more arched than
that of C. lateralis.