The Little Brown Myotis is a medium-size species of Myotis. Its fur colour is extremely variable: the fur on its back ranges from yellow or olive in populations from the dry interior to blackish in coastal populations. The fur on its underside is lighter, varying from light brown to tan. Its dorsal fur is long and glossy. The wing membranes and ears are dark brown. The ears reach the nostrils when pushed forward; the tragus is blunt and about half the ear length. The calcar is not keeled. The skull is typical of most Myotis species; the forehead has a gradual slope.
IdentificationThe ear and tragus of the Little Brown Myotis are smaller than that of the Fringed Myotis (Myotis thysanodes), Northern Long-eared Myotis (Myotis septentrionalis), Western Long-eared Myotis (Myotis evotis) and Keen's Long-eared Myotis (Myotis keenii). The absence of a keel on the calcar distinguishes it from the Long-legged Myotis (Myotis volans), California Myotis (Myotis californicus) and Western Small-footed Myotis (Myotis ciliolabrum). The Yuma Myotis (Myotis yumanensis) is smaller (forearm usually less than 36 mm) with duller, shorter fur. Nevertheless, in some parts of the province, such as the Okanagan Valley, the Little Brown Myotis can be extremely difficult to distinguish from the Yuma Myotis. Behaviour may assist in identification. The Little Brown Myotis tends to be more aggressive than the Yuma Myotis when handled. Skull features will give a more reliable identification: Little Brown Myotis has a longer skull (greater than 14 mm) that has a more gradually sloping forehead; but even these characteristics are not always reliable in identifying some individuals with intermediate skull features.
Dental Formulaincisors: 2/3
Measurementstotal length: 86 (70-108) n = 383
tail vertebrae: 37 (25-59) n = 379
hind foot: 10 (6-13) n = 385
ear: 13 (9-17) n = 217
tragus: 7 (4-10) n = 151
forearm: 36.4 (33.0-40.3) n = 295
wingspan: 248 (224-274) n = 151
weight: 6.2 (6.2-10.2) n = 98