Gray Bat - Cave Gating

Cave Gating

Many factors play an important role in determining a viable habitat for M. grisescens. Among these are the natural characteristics of the cave entrance, physical features of the cave, and surface climate. These contributing factors play an especially important role in determining the internal conditions that foster cave fauna. Because the gray bat is a cave dwelling species, its range is limited to caves whose internal conditions are favorable. Human intervention has caused a precipitous decline in the number of suitable caves for the gray bat. Thus, in order to maximize the gray bat’s range, the United States government is funding cave gating programs. Cave gating is an accepted method in protecting cave dwelling species as it limits the impact of human disturbance upon internal cave conditions. In constructing internal cave gates, several key parameters were implemented to minimize changes in the airflow through the cave and the ability of the bats to either access or leave the cave. With these limitations in mind, the internal cave gating was placed 5 to 15 meters in advance of historically critical roost areas. In addition, a 15 cm clearance between bars of the gating was allowed to ensure unobstructed flight into and out of the cave. Early cave gating methods that did not account for these factors frequently led to cave abandonment. In assessing the proficiency of cave gating, two metrics were established: population dynamics before and after the construction of cave gate and initiation of emergence from the cave. Population estimates were derived from the accumulation of bat guano. More guano indicated the presence of a larger population. In manipulating the emergence of gray bats from the caves under study, infrared light sources were used. Observations of the frequency of emergence of the bats from open caves and gated caves confirm that gating is not an impediment. Gated entrances, however, have provided new opportunities for natural predators of gray bats. Because gates sometimes require the bats to fly slower, as well as providing hunting perches to predators within reach of emerging bats, natural predation may be increased by cave gating.