WESTERN YELLOW BAT
Dasypterus xanthinus Thomas 1897
Order Chiroptera : Family Vespertilionidae
DESCRIPTION. Very similar in appearance to Dasypterus ega. Dorsal coloration is a pale yellow; brighter yellow hairs of the interfemoral membrane contrast with dorsal coloration. Lacks a dark face mask. Maxillary tooth row length in females, 5.7–5.9 mm. Averages for external measurements: total length, 105 mm; hind foot, 10 mm; ear, 13.5 mm; forearm, 45 mm. Weight, 12–19 g.
DISTRIBUTION. Dasypterus xanthinus occupies the dry, thorny vegetation of the Mexican Plateau, coastal western Mexico including parts of Baja California, and the deserts of the southwestern United States. Its occurrence in Texas is very recent (1990s), having been recorded first from both Big Bend National Park and Black Gap Wildlife Management Area in Brewster County, and subsequently from the Davis Mountains, Jeff Davis County, to the north, from Del Rio, Val Verde County, to the east, and from El Paso County to the west.
SUBSPECIES. Monotypic species.
HABITS. This species represents a recent addition to the fauna of Texas. All evidence suggests that this addition is a result of an expansion of the range of the species rather than the absence of previous collecting success. The reasons for a range expansion by this species are not well understood, but the most probable explanation is the warmer temperatures recently associated with western Texas. Vegetational changes in the region also may have facilitated the northward range expansion of the species. Cottonwood trees and other riparian vegetation in the Trans-Pecos region were almost exterminated early in the twentieth century, but the establishment of Big Bend National Park and other protected areas in the region has allowed the recovery of natural vegetation. This woody, riparian growth provides suitable roosting habitat for D. xanthinus. Western yellow bats have been found using giant dagger yucca (Yucca carnerosana) as a roost site in Texas.
Although only eight specimens have been reported from West Texas, the Black Gap and Davis Mountains specimens were captured during the summer, and the Davis Mountains specimen was a lactating female, suggesting that a breeding population of this species occurs in the region. Its reproductive biology is probably similar to that of the southern yellow bat (D. ega), with one notable difference: litter size is typically two, as opposed to two to four as seen in other yellow bats.
Little is known of the diet of D. xanthinus. A fecal sample from one specimen collected during the fall in Big Bend National Park contained the remains of true bugs, flies, ants, moths, beetles, and grasshoppers.
POPULATION STATUS. Rare, year-round resident. The western yellow bat is an excellent example of a species that has recently invaded Texas in the Trans-Pecos region of the state. Collecting records suggest it is rare, although not as rare as Lasiurus blossevillii, Myotis occultus, or M. septentrionalis.
CONSERVATION STATUS. This species' status is listed by the IUCN as least concern because of its wide distribution, presumed large population, and occurrence in a number of protected areas. At this time the western yellow bat is not listed on the federal or state lists of concerned species. Its complete distribution and population abundance must be studied before its conservation status can be accurately determined. There appears to be an established population in Brewster County where it is encountered most often in the fall.
REMARKS. Until very recently the western yellow bat was considered to be conspecific with the southern yellow bat, D. ega. Recent karyotypical and electrophoretic studies by Robert J. Baker and his students at Texas Tech University, however, have shown that not only are ega and xanthinus specifically distinct, but that xanthinus is more closely related in an evolutionary sense to D. intermedius than it is to ega.
The application of the generic name Dasypterus for the yellow bats (previously included in the genus Lasiurus) follows the work of Amy Bickham Baird and John Bickham, as described in the account of Lasiurus blossevillii.
From The Mammals of Texas, Seventh Edition by David J. Schmidly and Robert D. Bradley, copyright © 1994, 2004, 2016. Courtesy of the University of Texas Press.