Myotis yumanensis
Yuma myotis

Myotis yumanensis is found in western North America, ranging from British Columbia to Central Mexico and eastward to Colorado (Whitaker, 1996) and as far east as Oklahoma (Barbour and Davis, 1969).

Myotis yumanensis is found in a variety of habitats, ranging from juniper and riparian woodlands to desert regions near open water (Nowak, 1991). One is almost guaranteed to find this species wherever there are rivers, streams, ponds, lakes, etc. In fact, M. yumanensis is more closely associated with water than any other North American species of bat (Barbour, 1969). When not near water over which to forage, these animals can be found in the thousands roosting in caves, attics, buildings, mines, underneath bridges, and other similar structures. Little is known about the migration of this species. However, it has been recorded in Texas as well as in its normal range during the winter season (Allen, 1994).

Myotis yumanensis is a small species of Myotis, with a body length of 84 to 99 mm and a tail length from 32 to 45 mm. Their forearms are 33 to 37 mm long and the overall wingspan is about 235 mm (Barbour, 1969). The skull is shortened (usually less than 14 mm) and does not have a sagittal crest. Teeth include somewhat small and separated incisors with dilambdodont molars. Other distinguishing features include an unkeeled calcar and no nose leaf (Nowak, 1991).

Myotis yumanensis has short fur shaded tan or brown on top, with whitish or buffy underparts (Whitaker, 1996). Yuma myotis resemble M. lucifugus but the latter is larger and has shinier fur. (Barbour and Davis, 1969; Nowak, 1991; Whitaker, 1996)

Ovulation and fertilization occur only in the spring (Nowak, 1991). Sperm are held in the reproductive tract of females over the winter. Females give birth to only one young and usually do so between May and June (Allen, 1994). During birth, they sit upright and catch the newborn with the uropatagium (Creech, 1996). Females aggregate (in caves, abandoned buildings, or anywhere else that has a high and stable temperature of 86 to 131 F) in maternity roosts sometime around April (Whitaker, 1996). Males are usually absent from these maternity colonies and remain solitary as the young are being reared. During this time, almost all of the females in the population have a newborn (Barbour and Davis, 1969). (Allen, 1994; Barbour and Davis, 1969; Nowak, 1991; Whitaker, 1996)

Like most bats, M. yumanensis is nocturnal. Not long after sunset these bats become active and start to call; however they do not emerge until dark (Barbour and Davis, 1969). Once they have emerged from their roosts, they fly very low over surfaces of water to feed, and after feeding for several minutes they begin to drink. These bats usually disappear 2 hours after dark, suggesting remarkable efficiency in hunting. They are suprisingly inconsistent and fluttering in their flight (Allen, 1994). When roosting, they hang on a vertical surface by their thumbs and toes with their wings tucked alongside their bodies (Nowak, 1991). (Allen, 1994; Barbour and Davis, 1969; Nowak, 1991)

Myotis yumanensis is a very efficient insectivorous feeder that begins foraging at dusk and usually finishes two hours after sunset (Barbour and Davis, 1969). These bats usually feed over water, and their prey primarily consists of moths, midges, caddisflies, craneflies, beetles and other various small insects (Whitaker, 1996). Like most bats, they locate insects in flight by emitting ultrasonic sounds (echolocation). Then they either catch the insects in their mouths or use their tail membranes as a pouch in which to snare larger prey.

All insectivorous species of bats are seen as a safe and sensible means of pest control on agricultural crops. A Yuma myotis can consume up to half of its weight every night feeding on moths, beetles, flies, etc. (Nowak, 1991).

All bats, including Yuma myotis, have been known to carry diseases such as rabies, as well as mites, and fleas (Creech, 1996). This becomes problematic to humans mainly if they handle wild bats without prior knowledge of their health status.

This species of Myotis is commonly observed. There has been a slight decline in the number of these bats due to destruction of suitable roosting sites.

Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Myotis yumanensis mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)

There are five subspecies of M. yumanensis in the United States: M. y. yumanensis (found in the southwestern desert), M. y. phasma ( found in Utah and Colorado), M. y. sociabilis (found in California and Canada), M. y. oxalis (found in the San Joaquin Valley), and M. y. saturatus ( found along the Northwestern Coast) (Barbour, 1969).