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  The Mammals of Texas - Online Edition

Spotted Bat
Order Chiroptera : Family Vespertilionidae : Euderma maculatum (J. A. Allen)

Spotted Bat (Euderma maculatum).  Photo by Merlin D. Tuttle, Bat Conservation InternationalDescription. A moderately large bat with extremely large ears and a conspicuous dorsal color pattern of three large white spots, one on each shoulder and one on the rump, on a black background; a small white patch at the base of each ear; hairs on the underparts with white tips and blackish bases. Ears and membrane in living individuals pinkish; pale brownish in preserved specimens. Dental formula: I 2/3, C 1/1, Pm 2/2, M 3/3 X 2 = 34. External measurements average: total length, 124 mm; tail, 51 mm; ear, 42 mm; forearm, 51 mm. Weight, 16-20 g.

Distribution in Texas. The semi-arid regions of the western United States and northern Mexico from southwestern Idaho and south-central Montana southward to the Mexican states of Durango and Queretaro. Known in Texas only from specimens captured in the Big Bend National Park, Brewster County.

Habits. Although unmistakable in appearance, the spotted bat is one of the least understood of American bats, primarily because of its relative scarcity, at least in collections. There have been scattered records of this bat throughout the western United States dating back to 1891, but it has been taken with any regularity only in California, Arizona, New Mexico, southern Utah, and southern Colorado. It was first found in Texas by David Easterla, who captured two adult females in early August, 1967 in mist nets set above a pool in a shallow, barren, hot, dry canyon in the Big Bend National Park.

The infrequency of capture of this bat has caused much confusion and speculation regarding its habitat. Several authors have reported captures in pine forests at high elevations (2400 m); others from a pinyon pine-juniper association; and still others from open scrub associations in desert areas. One worker has suggested that females give birth to their young in forested situations and later move to the lower elevations; another suggests that the bat is a cliff-dweller and roosts in cracks and crevices of canyon walls. A large number of the known specimens were captured in mist nets set over permanent streams or water holes adjacent to steep cliffs in open scrub desert country.

Little is known of the behavior of the spotted bat except that it appears to be most active well after dark. Most individuals caught in mist nets set over water, where bats come to drink, have been captured after midnight. Easterla speculated that its swoop over a water hole is made at relatively high speeds because several of the bats he has captured have been injured when they struck the nets. While in flight the bat emits a series of strident "tics" similar to, but higher pitched than, those of the Mexican big-eared bat Idionycteris phyllotis. Several authors have commented on the docile disposition of captive spotted bats, but occasional individuals are ill-tempered. Available data indicate that moths are highly important in their diet. In fact, these bats may feed almost exclusively on moths.

Data on reproduction are sparse. A gravid female captured by Easterla on June 11, in Big Bend National Park, gave birth a few hours later to a single male baby that weighed 4 g (one fourth of his mother’s weight!). One of two females Easterla captured in the park in early August was lactating; the other was in a post-lactating condition. Two females captured June 30 and July 1 in Catron County, New Mexico, were in postpartus condition and lactating, as were three females collected in Garfield County, Utah, in mid-August. Thus, it appears that a single offspring is born to each sexually active female in June or July.

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