Bats face threats from many sources: the loss of roosting and foraging habitat from development (urban expansion, habitat conversion, timber removal, active mining and solar and wind development); toxic contaminants; public health policies and white nose syndrome (WNS). Different bat species may be impacted by several of these factors. Colonial bats present an opportunity to monitor the effects through standardized annual evening exit counts during a time when the population is stable, such as a maternity colony before any of the pups have fledged. Equipment might vary and evolve over time, but the environmental cues that the bats use to time their nightly emergence remain the same: weather (temperature, rain and wind) and moon phase. The latter factor may affect different colonies and species in different ways and must be calibrated by counting the exodus twice: during the week before the full moon and again within the same week after the full moon.

Patricia Brown received her PhD from UCLA in 1973 studying the ontogeny of echolocation and communication in pallid bats. She was a Research Associate at UCLA until retirement in 2010. She has consulted with government agencies and private entities on surveys, threats and conservation of bats, especially colonies roosting in mines.