Eastern Pipistrelle
Order Chiroptera : Family Vespertilionidae : Pipistrellus subflavus (F. Cuvier)

Description. A small bat with leading edge of wing and the edges of the membrane between the hind legs much paler than rest of membranes; tragus long and slender; upperparts pale yellowish brown, with grizzled effect; the individual hairs tricolored, dark basally, grayish-yellow medially, and tipped with dusky. Dental formula: I 2/3, C 1/1, Pm 2/2, M 3/3 X 2 = 34. External measurements average: total length, 85 mm; tail, 41 mm; foot, 8 mm; ear, 14 mm; forearm, 35 mm. Weight, 4-6 g.

Distribution in Texas. Eastern half of state including the Rolling Plains west to Armstrong County and central Texas as far west as Val Verde County, and a recent record from Lubbock County.

Habits. These small bats are some of the earliest to emerge in the evening from their daytime retreats in caves, crevices in cliffs, buildings, and other man-made structures offering concealment. They are relatively slow and erratic in flight and often flutter and flit along watercourses or over pastures and woodlands like large moths. They appear to favor watercourses as foraging grounds. They are much more closely associated with woodlands than is the western pipistrelle.

This species is known to spend the winter hibernating in suitable caves within its summer range. Its hibernation is more complete than that of most other American bats and they generally roost singly or in small groups. Individuals may hang in one spot for weeks on end, and their torpor is so deep that they are not easily disturbed. They emerge from hibernation early in the spring and remain active well into the fall.

Little is known of their food habits in Texas. In Indiana they are known to eat small leafhoppers, ground beetles, flies, moths, and ants. Insects are caught by the bats in considerable quantities in a short period and within 20 minutes they are gorged. They probably feed at intervals throughout the night and hang up to digest their meals between feeding times.

Mating takes place in the fall. They have been observed copulating as late as November. Both males and females have been observed roosting together as early as August, however. During the period from March to August adult males and females usually occupy separate roosts. Data suggest that the sperm may remain viable in the vaginal tract of the female until spring, when ovulation occurs (in March or April) and fertilization of the ova takes place. However, copulation in the spring also has been observed.

The exact period of gestation is not known, but it probably does not begin until the bats have left their winter quarters. The young, usually two in number, are born from May to July. They grow rapidly and when about 3 weeks old are able to take care of themselves.

Photo credit: John L. Tveten.