|The Mammals of Texas -
Attwater's Pocket Gopher
Rodentia : Family Geomyidae : Geomys
Description. This pocket gopher
closely resembles the Plains pocket gopher (Geomys
bursarius) and Bairds pocket gopher (G. breviceps). Morphologically, the
three are nearly identical and extremely difficult to
distinguish in the field. G. attwateri is
intermediate in size between G. breviceps (larger)
and G. bursarius (smaller). A cranial feature used
successfully in separating these species is the length of
the jugal bone on the zygomatic arch compared with the
width of the rostrum ventral to the infraorbital
openings. In G. bursarius, the dorsal exposure of
the jugal is longer than the width of the rostrum,
whereas in G. attwateri and G. breviceps
the dorsal exposure of the jugal is shorter than the
width of the rostrum.
The best distinguishing feature is the
karyotype, which in G. attwateri has a diploid
number of 70 and a fundamental number of either 72 or 74.
External measurements average: total length, 216 mm;
tail, 62 mm; hind foot, 26 mm. Dental formula as in G.
Distribution in Texas. From the Brazos
River in eastern Texas south to southern Texas near the
San Antonio River and along the coast from Matagorda to
San Patricio counties.
Habits. The general habits of G.
attwateri are similar to G. bursarius and G.
breviceps. Attwaters pocket gopher is also an
opportunistic herbivore, consuming a wide range of
perennial and annual plant species. On the Welder
Wildlife Refuge in South Texas, these gophers consume 41
of the 51 plant species available to them.
In contrast to the burrow systems of
the plains pocket gopher, burrows of Attwaters
pocket gopher tend to be more circuitous in nature. Their
burrows are nonlinear and have few lateral or blind
branches. This may be in response to a localized, or
"clumped," distribution of resources,
adaptations to low population densities, or their social
G. attwateri is active at all
hours of the day. Peaks in daily activity are not known.
Attwaters pocket gopher breeds
from October through June with peaks in December-January
and April-May. Little, if any, breeding occurs during the
summer months of July, August, and September. Females
produce an average of two or three young per litter and
at least two litters per year.
Remarks. A small zone of contact
between G. breviceps and G. attwateri
occurs just west of the Brazos River in Burleson County.
Of 42 gophers collected in this area, 31% had an apparent
karyotype intermediate between the two species,
indicating that hybridization may occur in the wild. In
general, the range of G. attwateri is limited on
the north by the Brazos River, although small zones of
contact with G. breviceps (the range of which is
limited on the south by the Brazos River) may occur where
the Brazos River has periodically changed course in the