David's Myotis

David's myotis is a small mouse-eared bat, slightly larger than Brandt's bat in the European comparison used by BatMonitoring. Head-and-body length is 38–50mm, forearm 31–37mm, and weight 4–7.9g. Dorsal fur is dark brown, sometimes reddish, with paler hair tips; the underside is paler and greyer. Measurements or acoustic evidence are preferable because small Myotis can be difficult to separate visually. (BatMonitoring species account)

Modern taxonomy includes populations formerly called the steppe whiskered bat, Myotis aurascens, within M. davidii; NCBI also lists aurascens and hajastanicus as synonyms. The species occurs in Mongolia, China, Kazakhstan, and Russia. This shifting species boundary makes older records especially important to check against their original identification criteria. The opened sources did not support a Mongolia-specific habitat, diet, breeding schedule, or named viewing locality. (NCBI Taxonomy; Wikipedia, general species account)