Attwater's Pocket Gopher
Order Rodentia : Family Geomyidae : Geomys attwateri Merriam

Description. This pocket gopher closely resembles the Plains pocket gopher (Geomys bursarius) and Baird’s 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. bursarius.

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. Attwater’s 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 Attwater’s 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 structure.

G. attwateri is active at all hours of the day. Peaks in daily activity are not known.

Attwater’s 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 past.