Southern Yellow Bat
Order Chiroptera : Family Vespertilionidae : Lasiurus ega (Gervais)

Description. A yellowish-brown bat similar to Lasiurus intermedius but smaller. Dental formula: I 1/3, C 1/1, Pm 1/2, M 3/3 X 2 = 30. External measurements average: total length, 118 mm; tail, 51 mm; foot, 9 mm; forearm, 47 mm. One of the best characters to distinguish L. ega from L. intermedius is the length of the maxillary toothrow: in ega it is less than 6.0 mm, in intermedius more than 6.0 mm.

Distribution in Texas. This is a neotropical species that reaches the United States in southern California, southern Arizona, and southern Texas where it has been recorded from Cameron, Kleberg, and Nueces Counties. Its range extends southward east of the Andes to Uruguay and northeastern Argentina.

Habits. Like other members of the genus Lasiurus, southern yellow bats are associated with trees which can provide them with daytime roosting sites. In the vicinity of Brownsville, numbers of them inhabit a natural grove of palm trees (Sabal texana). L. ega may be a permanent resident in that area because they have been captured there in six different months of the year, including December. These bats may be increasing their range in Texas due to the increased usage of ornamental palm trees in landscaping.

These bats feed on insects which they probably capture in flight. Bats observed in the Mexican state of San Luis Potosi started foraging about dusk. Nets stretched over ponds at which bats came to drink did not catch any L. ega until about 2 hours after darkness. Stomachs of those captured at that time were crammed with insect remains.

The breeding season is in late winter in the South Texas area. Six females captured in late April all carried embryos; one with two very small (3 mm crown-rump length) embryos; the other five with three embryos each, the crown-rump length of which ranged from 11 to 14 mm. Of 11 females captured on June 8, only one was pregnant. She contained four embryos whose average crown-rump length was 25 mm. Nine of the other 10 females were lactating. Three females captured in June in the neighboring Mexican state of Tamaulipas were also lactating.

Photo credit: Merlin D. Tuttle, Bat Conservation International.