The Allen's big-eared bat is similar in apperance to the Townsend's big-eared bat displaying disproportionately large ears and convoluted nasal folds. Since this species has yet to be captured in Colorado measurements are based on other locales. Total length is 103-121 mm; tail length is 46-55 mm; hindfoot length is 9-12 mm; ear length is 38-43 mm; forearm length is 43-49 mm; and wingspan is 31-34 mm (Armstrong et al. 2011).
Long believed to be a resident in Colorado it was not until 2008 when Mark Hayes and colleagues (Hayes et al. 2009. ). Currently, suggested range in Colorado is restricted to the southwestern counties.
The Allen's big-eared bat is associated with shrublands, ponderosa pine lands, and pinon-juniper woodlands, and has been captured in riparian cottonwood galleries. The recordings in Colorado were made along the La Sal Creek canyon in Montrose County
Little is known of the Allen's big-eared bat's reproductive ecology. In the spring, females segregate from males to form maternity colonies. Of the few maternity colonies known they ranged in size from 25 - 97 individuals and were in mine tunnels or a pile of rubble near a grotto. Females typically have 1 young that are volant by mid-summer (Czaplewski, N.J. 1983. Idionycteris phyllotis. Mammalian Species 208:1-4.)
Allen's big-eared bats appear to be moth specialists, but also eat various beetles and ants. It is believed that they will glean insects off of vegetation and can take insects in flight (Czaplewski 1983).
The Allen's big-eared bat tends to feed later in the evening and recordings from Colorado were made between 9 pm and 2:30 am (Armstrong et al. 2011). This species has not been captured in Colorado despite much effort by Mark Hayes and colleagues.
Hayes, M. A., K. W. Navo, L. R. Bonewell, C. J. Mosch, and R. A. Adams. 2009. Allen's big-eared bat (Idionycteris phyllotis) documented in Colorado based on recordings of its distinctive echolocation call. Southwestern Naturalist 54(4):499-501.