Night Roosting Behavior in Four Species of Desert Bats

Abstract

Various aspects of night roosting behavior were observed for four species of desert bats. Variability in night roost utilization was found for those species for which adequate observations were available. Myotis californicus roosted primarily in desert shrubs or trees, depending on availability. Pipistrellus hesperus utilized rock, rock crevices, and desert shrubs as primary roosting sites, rock being preferred when in close proximity to water. Antrozous pallidus was more flexible in roosting behavior, utilizing small trees, rock crevices, and an abandoned shed. In contrast, Tadarida brasiliensis roosted in a bridge expansionjoint where they were also found during daylight hours. Night roosting for digestion and subsequent weight loss reduces wing loading, thereby allowing considerable energy conservation in further foraging activity or long flights back to day roosts. During daylight hours, bats seek shelter in a wide variety of habitats. Day roosts have been described in numerous previous studies. Existing data on night roosts, however, are limited and have resulted mainly from accidental encounters in buildings, bridges, mines, caves, and rock crevices (Barbour and Davis 1969). In desert areas bat activity is concentrated near free water, which may be located at a considerable distance from roosting sites. There are, however, numerous isolated mountain ranges and adequate vegetation which could provide suitable night shelter. Where typical roosting sites occur adjacent to a water source, night roosts for some species of desert bats have been described (Dalquest 1953; Krutzsch 1954; Orr 1954; Cross 1965; Barbour and Davis 1969; Poche and Ruffner 1975). In this study we attempted to locate and describe night roosts in areas of the Mojave Desert where night roosts have not previously been identified. MATERIALS AND METHODS. Bats used for roosting behavior observations were collected at various locations in southern Nevada and northern Arizona (600-1480 m elevation) during the period July-September 1975. Roosting behavior observations were made on 34 Myotis californicus, 32 Pipistrellus hesperus, 26 Antrozous pallidus, and 24 Tadarida brasiliensis.