Roost Characteristics and Clustering Behavior of Western Red Bats (Lasiurus blossevillii) in Southwestern New Mexico

The western red bat (Lasiurus blossevillii) is a foliage-roosting species of riparian habitats in arid regions of the southwestern United States. Only limited published anecdotal observations exist for roost sites used by this species. Western red bats were split taxonomically from the eastern red bat (Lasiurus borealis) in 1988, but summaries of roosting behaviors for western red bats still appear to stem from former associations with the commonly studied eastern red bat. Our study represents the first comprehensive research on the roosting ecology of western red bats. We radio-tracked 14 adult bats to 19 different day roosts along the Mimbres River of southwestern New Mexico. While we documented that western red bats had an affinity for densely foliated trees (79%), we did not detect any selection for tree species or size. At our study site, western red bats roosted in cottonwoods (47%, Populus spp.), velvet ash (21%, Fraxinus velutina), box elder (16%, Acer negundo), and red mulberry (16%, Morus rubra). We also described clustering behavior, where groups of 2-3 adults roosted in direct contact with one another. Although the species was deemed to roost solitarily, the frequency of clustering behavior in our study suggests otherwise. If bats were observed in clusters, they typically exhibited greater roosting fidelity than solitary individuals. Because arid riparian corridors in the southwestern United States generally are considered threatened systems, protection and preservation of mechanisms that create and maintain the diversity of these riparian corridors is necessary for the survival of this uncommon and poorly understood species.