This is Colorado's only medium-sized, short-eared myotis with a keeled calcar (the spur of bone that projects inward from the ankle and helps to support the uropatagium). It is a fairly heavy-bodied bat, and the medium to dark brown fur on the back extends to the tail membrane. The short ears appear more round, less pointed than those of other species. Hairs of the venter are paler than those of the back and may even be buffy. The underside of the wing usually is well furred to the elbow. Tips of individual hairs may appear slightly burnished. Mean measurements of six males and nine females from Park County were: length, 97.3 and 102 mm; length of forearm, 37.8 and 38.2 mm; weight, 8.7 and 11.2 g. The wingspan is 250-270 mm. The species most readily confused with the long-legged myotis is the little brown bat, which differs in having relatively longer ears, lacking the distinct keel on the calcar and frequently having paler pelage.
This species occurs throughout much of western North America from central Mexico to extreme northwestern British Columbia and from the Pacific Coast to the western margins of the Great Plains. The animals occur across the western three-fifths of Colorado and the wooded mesas of southeastern Colorado at elevations ranging from about 5,000 to 11,500 feet. This is the most common myotis at higher elevations in the state.
The long-legged myotis is a species of wooded areas in foothills, mountains and high plateaus. Typical habitat is montane or subalpine forest, ponderosa pine woodland, piñon-juniper woodland and montane shrubs with willows or well-watered stands of sagebrush. The animals roost by day in buildings, mines, fissures in rocks or beneath loose bark on trees. Usually they roost singly or in small groups. Night roosts are in dark places like caves or mines. Winter haunts of Colorado individuals are unknown, but they may hibernate locally, with only short migrations, as late fall activity has been observed at mines and caves. Elsewhere, they are known to hibernate in mines or caves.
Pregnant females form small nurseries of up to several dozen individuals in buildings, crevices or trees. Males are segregated and solitary during the maternity season. In Colorado, males with scrotal testes have been captured in July and August. It has been noted that the long-legged myotis has a particularly long parturition season. Pregnant females have been noted from June to early August in Colorado and elsewhere, and births are spread throughout the summer. Lactating females are most abundant in samples beginning in August. Females apparently breed their first winter. Reproduction in this species has not been studied in detail.
The long-legged myotis mostly eats moths. They emerge to feed early (while it is light enough to observe them distinctly) and forage at heights of 3 to 4 meters over ponds, streams, open meadows or forest clearings, cruising a repetitive circuit through the evening. Flight is more relaxed and leisurely than that of other medium-sized species of Myotis, and experienced observers can distinguish it by the flight pattern.