| Abandoned mines are increasingly important for bats that depend on subterranean habitat due to disturbances occurring at natural cave roosts (e.g. commercial development, recreation). Abandoned mines, however, pose risks to public safety such as collapsing, and presence of poisonous gases. The Abandoned Mine Land Program was created to mitigate these safety hazards, while also safeguarding important wildlife habitat with gates. We reviewed 22 studies from North America, Australia, Europe, and Asia that documented responses of bats to gates and found that although bats displayed a negative short-term response (e.g., increased energetically-demanding flight behaviors), mid to long-term responses to gates varied from negative to positive (e.g., population trends remained stable, increased, and decreased).;We tested effects of gate design on bats at 3 temporal scales. Our objectives were to determine 1) short-term (1 week) bat behavioral responses to gating, including gate material used and height above ground, 2) midterm (<1 year) changes in bat use (i.e., activity levels, roost type, species composition) at abandoned mines before and after gate installation, and 3) long-term (4 to 20 years) changes in use (i.e., species presence, richness) at gated abandoned mines and factors (e.g., gate type, mine complexity) influencing species presence. We used a mock gate experiment to test short-term effects, a midterm study to investigate changes in bat use before and after gate installation, and a genetic assay to test for presence of bats in gated mines for our long-term study. Consistent with our literature review, we found bats responded negatively in our short-term test; they increased energetically-demanding behaviors when a culvert gate was installed. We did not, however, detect a difference in responses to two factors expected to affect behavior: gate material (metal, high density polyethylene) or height above ground (0.15 m, 1.15 m). A less maneuverable species, the Mexican free-tailed bat (Tadarida brasiliensis), circled, collided, and landed on gates more frequently than an agile species, the California leaf-nosed bat (Macrotus californicus). In our midterm study, we found that bats continued to roost in abandoned mines gated up to 10 months and activity levels remained stable or increased at 73% of mines. Because decreases in use occurred at control (ungated) and gated mines, the decrease in activity we found could be a response to the gate (e.g., reduction of portal area by installation of the gate) or to other factors such as inter-and intra-seasonal variation in roost use. In our long-term study, 12 species including 2 subterranean obligate species (Townsend's big-eared bat [Corynorhinus townsendii], California leaf-nosed bat), continued to use abandoned mines with various gate designs. Mine characteristics (elevation, portal area, number of mine levels and entrances) rather than gate characteristics best predicted presence of Townsend's big-eared bats, California/Western small-footed myotis (Myotis californicus/ciliolabrum), fringed myotis (Myotis thysanodes), and cave myotis (Myotis velifer). We did, however, find that culvert gates positively influenced use of mines by the fringed myotis and negatively affected use by the cave myotis. Species-specific responses to gates exist and likely vary based on morphology, vocalization characteristics, and feeding behaviors of bat species. Responses from bats to gates shifted from short-term negative responses to more positive responses in our long-term study, so we conclude that gate age and mine characteristics are more important for most species than gate designs currently being used. Our study provides resolution and support to published literature on bat species acceptance of gates installed at abandoned mines. |
PDF Full Text Request