Euderma maculatum
spotted bat

The Spotted bat has a patchy distribution, occurring from northern Mexico to British Columbia. They are seldom abundant. Recorded observations extend from the Pacific coast to the Rocky Mountains inland.

Spotted bats have been found foraging in many different habitats, especially in arid or Ponderosa Pine forests, and marshlands. Because of the low frequency of their echolocation calls large open habitat is predicted to be preferred. However, it is believed that the distribution of suitable diurnal roosting sites is cause for the patchy distribution of this species. Spotted Bats roost in the small cracks found in cliffs and stony outcrops. They have been found as high as 3000m above sea level, and even below sea level in the deserts of California.

(Pierson and Rainey 1998; Poche 1981; Watkins 1977)

Total length, 126 mm; tail, 51 mm; hind foot, 12 mm; ear, 47 mm; forearm 48.51 mm. The Spotted bat is so named for its three white spots located over each shoulder and on the rump. The surrounding dorsal fur is black while the ventral fur is light with dark underfur. The face is black and the ears and wings are pale.

Very little is known about this species. It was once thought to be rare In the 100 years from the time of its discovery to 1990 only 14 individuals, for example, were collected in California. Since then the number of locations where spotted bats have been found in that state has tripled, and their range is now known to extend from Montana south to central Mexico, including in western US into arid parts of Nevada, Wyoming, Colorado, and Utah that were previously unrecognized. While the distribution is very patchy over this range, the species may be locally common. Typically at a given site usually only one is caught per night, and individuals are well dispersed, separated by distances of 750-1000m of each other. They use vocalizations to communicate with neighbors. There is at least one recorded account of an apparent territorial dispute involving vocalization and direct contact. Only in one study has this species been seen foraging in groups.

In most studies these bats forage no more than 10 km from their diurnal roost, and seem to forage constantly. Individuals fly in elliptical patterns from their roosting sites while foraging. However there is one recorded case of a lactating female flying 35.8 km straight from her diurnal roost around 23:00 h to a foraging site, roosting there for part of the night (0100 to 0330 h), and then flying back to the cliff day roost. Other bats at the same location followed that nightly pattern. This behavior could be the compromise these bats make between suitable diurnal roosting sites, and foraging sites. This species seems to be roost faithful; they return to the same diurnal roost every night in the summer. In the Autumn their behavior becomes less predictable.

Foraging behavior does not seem affected by amount of moonlight at night, in contrast to the foraging behavior of other bat species.

In addition to the nightly migration to foraging sites, these bats might have a seasonal elevation migration from Ponderosa pine high elevation habitats in June and July to lower elevations in August.

(Leonard and Fenton 1983, 1984; Navo et al. 1992; Perry et al. 1997; Pierson and Rainey 1998; Poche 1981; Storz 1995; Woodsworth et al. 1981)

Like most Microchiroptera, the Spotted bat is an echolocator, but uses very low frequencies to locate prey (9-12kHz). These frequencies limit the Spotted bat to catching large flying insects, apparently specializing on large moths that cannot detect echolocation calls of such low frequencies. Insects seem to be caught in the air at a rate of about one every 45 seconds, and most recorded foraging behavior occurred from 11 pm to 3 am.

(Wai-ping and Fenton 1989; Watkins 1977).

unknown

Unknown, but as a specialist on moths they might be important in controlling specific moth populations

Very little is known about the distribution of the population of this bat. The lack of natural history data places it in class 2, requiring more information. Because the Spotted Bat seems to forage in various habitats, conservation of diurnal roosts, rocky cliffs that have snug cracks for roosting, seem to be the best way to protect this species. However large open foraging sights, where their echolocation is most effective, are important to the conservation of this species, as well as the availability of large moths as prey.