||The Mammals of Texas -
Pocketed Free-tailed Bat
Chiroptera : Family Molossidae
: Nyctinomops femorosacca (Merriam)
Description. Similar to the Brazilian free-tailed
bat, Tadarida brasiliensis,
but the bases of the ears are joined at the midline;
second phalanx of the 4th digit less (not more) than 5
mm; anterior part of hard palate narrowly, rather than
broadly, excised; upper incisors placed close together,
their longitudinal axes nearly parallel, not convergent,
distally; the presence of a fold of skin stretching from
the inner (medial) side of the femur to the middle of the
tibia. This fold produces a shallow pocket on the
underside of the interfemoral membrane in the vicinity of
the knee, a structure to which the common name alludes.
Dental formula: I 1/2, C 1/1, Pm 2/2, M 3/3 X 2 = 30.
External measurements average: total length, 112 mm;
tail, 46 mm; foot, 10 mm; ear, 23 mm; forearm, 46 mm.
Weight, 10-14 g.
Distribution in Texas.
Southwestern United States and northwestern Mexico;
records from southern California, southern Arizona,
southeastern New Mexico, western Texas; southward in
Mexico to the state of Michoacan. Known in Texas only
from Big Bend National Park, Brewster County.
Habits. This species is an
inhabitant of semiarid desertlands. It has been found
using day-roosts in caves, crevices in cliffs, and under
the roof tiles of buildings. Nothing is known about the
winter habits of these bats; apparently, they are absent
from Texas during this time.
These bats leave their day roost late
in the evening to forage, exhibiting swift, powerful
flight. Philip Krutzsch recorded the following
observations made at a colony of 50-60 of these bats he
found at a daytime roost in a crevice in the face of a
cliff in San Diego County, California, on March 17. The
first bats left the colony at 6:15 p.m.; others followed
in twos and threes for another half-hour. The bats
dropped from 1 to 1.5 m before taking wing. Their flight
appeared to be a rapid, complete wing beat. When first
taking flight, they uttered a shrill, sharp,
high-pitched, chattering call, which was repeated while
the bats were in full flight. They also squeaked a great
deal while in the roost. He described the odor of this
bat as similar to that of the house bat, but not quite so
strong. Little data on their food habits are available.
The stomachs of thirteen bats captured in Big Bend
National Park were found to contain moths, crickets,
flying ants, stinkbugs, froghoppers and leafhoppers,
lacewings, and unidentified insects.
Data on reproduction in this species
are also scarce. Fifteen females captured at Big Bend
National Park between June 10 and July 12 each contained
a single embryo. Lactating females have been caught in
this area from July 7 to August 8, suggesting that a
single young is born to the female in late June to early
Remarks. There is some confusion
about the generic name of this bat and its relative, N. macrotis. Patricia Freeman, in a comprehensive study of
the family Molossidae world-wide, separated the New World
and Old World species of Tadarida (exclusive of Tadarida
brasiliensis) into two distinct genera
applying the name Nyctinomops to the New World
species. Other mammalogists, however, have not followed
this arrangement and place all of the Texas species in
the genus Tadarida.