: This is a medium-sized, small-eared, pale grayish to yellowish bat, its dark membranes contrasting fairly strongly with the fur. Among Colorado's species of Myotis, only the California myotis and the small-footed myotis are as pale in color. The small-footed myotis is more yellowish, less grayish and both it and the California myotis are smaller than the Yuma myotis. Total length is 86-88 mm; length of forearm, 34-38 mm; and wingspan, about 235 mm. Weight ranges from 3 to 5 g.
Distribution: The Yuma myotis occurs widely in western North America, from central Mexico north to British Columbia, Montana and southeastern Colorado. In Colorado these bats occur at moderate elevations in valleys on the Western Slope, in the San Luis Valley and on the eastern slope north to the vicinity of Colorado Springs. They don't seem common. Maximum reported elevation of occurrence in Colorado is about 7,900 feet at Conejos in the San Luis Valley.
Habitat and Habits: This is a species of dry shrubby country, but it appears to be tied more closely to water than any of Colorado's other bats. Typical habitat is in pi-on-juniper woodland and riparian woodland in semi desert valleys. The animals roost in caves, crevices or abandoned buildings and other structures. They forage over water, along streams, over springs, among riparian or shoreline vegetation. The Yuma myotis apparently does not hibernate in Colorado, but its winter haunts are unknown. They arrive in Colorado about April, and they become scarce in September.
Breeding: Breeding has not been studied much in Colorado, although lactating females have been captured and a nursery colony was discovered in 1990 in the Colorado National Monument. Elsewhere, the animals are known to form nursery colonies of upwards of several thousand individuals in caves or attics. Apparently all adult females in a population breed. A single young is born late in the spring or early in the summer. Small breeding colonies have been discovered in the southeastern part of the state, but not elsewhere in Colorado. Males are solitary as the young are reared.
Food: Food consists mostly of moths, flies and beetles, but also includes leafhoppers, caddis flies, lacewings and crane flies. The animals forage near water and take many aquatic insects. They are efficient feeders and can fill their stomachs in 15 to 20 minutes. They forage in early evening, usually along the main channel of a stream.