The Relative Activity Of Mouse-Eared (Myotis spp.) And Brown (Eptesicus spp.) Bats (Chiroptera: Verspertilionidae) In Five Habitat Types Around Spring Meadow Lake
The number of habitat types that bats can efficiently exploit may be limited by bat morphology (mass, wingspan, wing area, wing shape) and echolocation calls. Analysis of these characteristics can be used to predict which habitats bats are most likely to use. Slower, more maneuverable bats such as Myotis spp. should be able to exploit cluttered habitats in which prey densities are high, whereas larger, faster bats such as Eptesicus fuscus should be less able to use cluttered habitats due to an inability to maneuver efficiently in such habitats. I surveyed bats belonging to two genera, Myotis and Eptesicus, between 29 July and 30 August, 1997 at Spring Meadow Lake, a state recreation area on the western outskirts of Helena, Montana. Five habitat types were monitored for relative bat activity. The habitats were an open field (OP), a canopied area (CA) characterized by Salix spp., and three shoreline habitats representing low (SW), medium (ME), and high (TH) vegetation densities. Overall, bats were found to be most active at the shoreline sites of medium vegetation density, with relative abundance at other habitat types decreasing in the following order: SW, TH, CA/OP. Myotis spp. activity reflected this same trend. However, Eptesicus spp. activity was not significantly associated with any of the habitat types. Both field and canopy sites were virtually devoid of any bat activity. Greatest bat foraging activity (feeding buzz ratio) was associated with the ME habitat type, reflecting the overall relative abundance of bats. There was a significant difference in foraging activity between the ME and OP habitat types, but not between other habitat types for Myotis spp. Results are consistent with research showing that some species of Myotis favor aquatic habitats over terrestrial habitats. Greatest relative bat activity at shoreline sites of medium vegetation may reflect a cost-benefit “decision” to forage in an area in which the combination of prey density and extent of surrounding clutter enables the greatest net energy gain.