Description
Cinnamon-buff to dark brown above, buffy to pale gray below; hairs on back have long glossy tips; ear when laid forward reaches approximately the nostril; tragus about half as high as ear; calcar without keel; length of head and body 41-54 mm, ear 11.0-15.5 mm, forearm 33-41 mm; braincase rises gradually from rostrum; greatest length of skull 14-16 mm; length of upper toothrow 5.0-6.6 mm (Hall 1981).
Diagnostic Characteristics
Differs from M. sodalis in unkeeled calcar. Differs from M. austroriparius in smaller size, glossy rather than dull pelage, and usual absence of a sagittal crest. Differs from M. grisescens in banded dorsal hairs banded (vs. unicolored) and wing attached to the foot at the base of the toe rather than at the ankle. Differs from M. velifer in smaller size, glossy rather than dull pelage, and lack of sagittal crest. Differs from M. keenii and M. septentrionalis in shorter ears that do not extend beyond the nose when laid forward. Differs from M. volans in smaller size, glossy rather than dull pelage, and unkeeled calcar. Differs from M. yumanensis in larger size, larger skull (greatest length usually more than 14 mm rather than usually less than 14 mm), and usually glossy pelage rather than dull pelage. Differs from M. thysanodes in absence of a conspicuous fringe of hairs along the edge of the interfemoral membrane. Differs from M. californicus in larger size, unkeeled calcar, and skull rising gradually from rostrum. Differs from M. leibii in larger size and unkeeled calcar. (Hall 1981).
Habitat
These bats use a wide range of habitats and often use human-made structures for resting and maternity sites; they also use caves and hollow trees. Foraging habitat requirements are generalized; foraging occurs over water, along the margins of lakes and streams, or in woodlands near water. Winter hibernation sites (caves, tunnels, abandoned mines, and similar sites) generally have a relatively stable temperature of about 2-12 C (see Kunz and Reichard 2010). Maternity colonies commonly are in warm sites in buildings (e.g., attics) and other structures; also infrequently in hollow trees. Microclimate conditions suitable for raising young are relatively narrow, and availability of suitable maternity sites may limit the species' abundance and distribution.
Ecology
Winter concentrations may include tens of thousands of individuals. Survival rate is low during the first winter, higher in subsequent years.
Reproduction
Mating occurs usually in September-October. Ovulation and fertilization are delayed until spring. Gestation lasts 50-60 days. Reproductive females annually give birth to 1 litter of 1 young, late spring-early summer. Females produce first young usually in their first (Indiana, New Mexico) or second year (British Columbia) (Herd and Fenton 1983). In British Columbia, individuals may delay or forego reproduction in wet years (Grindal et al. 1992). Survival for a decade may be fairly common; a few live as long as 20-30 years; females may be reproductive to an age of at least 12 years (Hall et al. 1957, Keen and Hitchcock 1980). Most summer colonies range from 50 to 2,500 individuals (average 400) (Mumford and Cope 1964).