Assessment of Bridges in Eastern Montana to Identify Active Season Bat Roosts

Abstract

Bats fulfill important niches in the ecosystems they occupy and control insect populations that are agricultural pests. Bat species across North America face several significant threats including habitat degradation/roost disturbance, wind turbine-related deaths, and White-Nose Syndrome (WNS). In Montana, bat roost information has been lacking in the nine eastern counties where Northern Myotis (Myotis septentrionalis) is listed as Threatened, as well as a large number of additional central and eastern Montana counties. To identify active season roosts across these regions, I surveyed bridges for bat use. From the surveys, I established baseline knowledge about bat roosting preferences and the locations of active roost sites to monitor, which can be used to better inform conservation efforts. Survey data were collected from bridges in nine counties in Eastern Montana, as well as from bridges in eight counties in central Montana. Bridges surveyed were classified by roost type (day, night, maternity, none). Structural materials, surrounding habitat characteristics, and other attributes were recorded. Night roosts were the most common roost type, concrete bridges were the most used bridge type, and maternity roosts were only found in wooden bridges with ideal crevices. Results which show widespread use of concrete bridges as roosts, and the importance of ideal crevices for day and maternity roosting bats, are consistent with previous studies in western and central Montana. Ideal crevices are an important structural characteristic for bridge roosting bats, which, when implemented in bridge design, provide suitable habitat in the face of increasing urbanization and human disturbance.