|The Mammals of Texas -
Southern Yellow Bat
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
Photo credit: Merlin D. Tuttle, Bat Conservation