252 Ammospermophilus insularisis a high-pitched short trill, which apparently is especially
useful in the rocky open habitat on Espiritu Santo Island.
No genetic diff erentiation exists between A. insularis and the
mainland A. leucurus. However, the frequent absence of an
upper third premolar on the island species suggests that this
species should be at least a subspecies of Baja California
peninsular A. leucurus.
general references: Álvarez-Castañeda 2007; Best, Cae-
sar, et al. 1990; Helgen et al. 2009.
Ammospermophilus interpres
(Merriam, 1890)
Texas Antelope Squirrel
description: The dorsum is gray suff used with brown
near the head and along the front and hind limbs, grading to
gray through the tail. A single thin white line on each side
parallels the spine. The venter is white. The dorsal surface
of the tail darkens to black at the distal end; the ventral sur-
face is white with two black bands.
size: Both sexes—HB 226 mm (220–235 mm); T 74.2 mm
(68–84 mm); Mass 99–122 g.
distribution: A. interpres is found from New Mexico and
west Texas (USA) to Chihuahua, Coahuila, and Durango
(México).
geographic variation: None.conservation: IUCN status—least concern. Population
trend—no information.habitat: Texas antelope squirrels live in rocky habitats
on and around desert mountain ranges; they often can be
found in deserts, grasslands, and woodlands where boul-
ders occur in proximity to juniper (Juniperus) and large
shrubs.natural history: A. interpres is diurnal. It is active year-
round but may hibernate during periods of extreme cold, as
individuals accumulate fat deposits in the fall of each year.
Texas antelope ground squirrels are well adapted for climb-
ing trees and rocks. A. interpres lives in shallow (< 1 m)
inconspicuous burrows that lack a mound and are often
a s s o c i a t e d w i t h s t r u c t u r e s s u c h a s b o u l d e r s , t r e e s , or s h r ub s;
these squirrels may also use rocky crevices. A nest chamber
provisioned with bedding exists in each burrow system.
Breeding occurs each year in February; a single litter of 5–14
young is most common, but there may be two litters in the
mild climates inhabited by these squirrels. Litters emerge in
April. Texas antelope squirrels feed heavily on seeds, fruit,
and cactus, but they will also include insects in their diet.
Densities are low and patchy in all habitats. These squirrels
are extremely energetic and rarely remain motionless, ex-
cept when sitting on their haunches atop a tall boulder, cac-
tus, or shrub. Their alarm vocalization is a mellow rolling-
but-harsh trill that appears to be an adaptation to structurally
complex environments. When running, Texas antelope squir-
rels hold their tails curled over their backs. Due to their small
body size and diurnal habits, A. interpres is a likely prey of
foxes, coyotes (Canis latrans), procyonids, small felids, raptors,Ammospermophilus interpres. Photo courtesy Maryann
Eastman.