Myotis yumanensis
(Yuma Myotis)

Order: Chiroptera
Order Description: Bats
Family Description:

In Idaho, the upper fur is pale brown lacking the goldish sheen usually seen in little brown bats. The tail membrane often has hair dorsally and ventrally that extends to slightly beyond a line joining the knees. The ears are rounded, extend just past the muzzle, and are pale brown as contrasted to the darker ears of little brown myotis. The skull has a abrupt increase in height above the forehead, a condition also lacking in Myotis lucifugus. In spite of these differences, it is extremely easy to confuse Yuma myotis with little brown myotis, especially in limited light. Both species lack a keeled calcar Click word for definition, although an extremely small lobular piece of tissue is present along the calcar in many yuma myotis.

The western portion of British Columbia southeast into western Montana and the western half of Idaho. Largely absent in Nevada and Utah, this species is found in Colorado, New Mexico, and Arizona to central Mexico, and extends along the Pacific Coastal areas of Baja California, California, Oregon, and Washington. In Idaho, it has been collected in eleven counties.

Yuma myotis occur in a variety of western lowland habitats in areas of abundant water where it forages for insects just above the surface of slack water. It is an important riparian Click word for definitionspecies and likely been eliminated along many streams in western states. Summer roosts include crevices in cliffs, old buildings, mines, caves, bridges, and abandoned cliff swallow nests. No large winter concentrations of this species have been studied in Idaho.

Found in wide variety of upland and lowland habitats, including riparian situations, desert scrub, and moist woodlands and forests, but usually found near open water (more closely associated with water than most other North American bats.) In Idaho, inhabits wide elevational range.

Yuma myotis eat a variety of soft bodied small insects, especially moths and emergent aquatic insects including stoneflies and mayflies found near and over water.

Insectivorous Click word for definition. Small moths are believed to be primary food source; dipterans Click word for definitionand ground beetles are other common prey.

Little is known about the distribution and abundance of this species in Idaho and whether it migrates to areas outside of summer locations. It is probable that yuma myotis are highly susceptible to destruction of conditions favoring the production of tricopteran insects upon which they feed and nursery colonies may only occur in mines lacking human disturbance.

Hibernates Click word for definition/aestivates Click word for definition. Active at night; leaves daytime roosts to feed in early evening. Often forages over streams, flying just above water surface. May be locally abundant. Availability of daytime roosts may be limiting factor in some areas. Males are solitary during birthing season.

Mating likely takes place during the fall, and ovulation and implantation in spring. A single pup is produced in female-only maternity colonies that may occur in dome areas in mines with high humidity Pups are born in May to mid July, depending on weather conditions. The thermal conditions required to support nursery colonies in Hell's Canyon have been studied.

Maternity colonies form in April. Female first breeds in second summer, and produces 1 young, born late May-July (in western Oklahoma and Arizona, peak is apparently mid-June; in California, young are born apparently from late May to mid-June). ovulation Click word for definitionand fertilization Click word for definitionare delayed until spring. Colonies disperse by end of September.

Status: Unprotected nongame species
Global Rank: G5
State Rank: S3

Important State References:
Betts, B.J. 1997. Microclimate in Hell's Canyon mines used by maternity colonies of Myotis yumanensis. Journal of Mammalogy 78:1240-1250.

Keller, B.L. 1987. Analysis of the bat species present in Idaho, with special attention to the spotted bat, Euderma maculatum. Dept. Biol. Sciences, Idaho St. Univ., Pocatello. 25pp

Information written by Barry Keller,© 2000
Map image provided by
Stephen Burton,© 2000
Design by Ean Harker©1999, 2000.