in the maternity colony until they are able to fly. Most young take flight by four weeks of age (late June to mid-July). Energy expenditure and growth Gray bats, as is the case in other organisms, acquire and use energy for growth and maintenance of their bodies before reaching sexual maturity, at which point much of their energy expenditure is devoted to reproductive processes. Gray bats prefer caves located near appropriate foraging sites to reduce the energy costs of flying long distances to find food. Gray bats roost in large colonies to reduce the cost of temperature regulation on the individual. Female bats must maintain relatively high body temperatures in comparison to the cooler temperatures of the cave during lactation, requiring large amounts of energy. During the peak lactation period, when young are roughly 20–30 days old, females may spend as many as 7 hours a night feeding. Because of the high energy demands on the females, larger roosts are more beneficial so that all may share the burden of maintaining body temperature. The formation of large colonies does at some point, however, have a negative trade-off. As the size of the colony increases, intraspecific competition for food resources increase, forcing an individual to forage over a larger range. This increased foraging range will lead to greater energy expenditure, potentially reducing growth in gray bat juveniles. The distance a gray bat travels from the roosting area to foraging area has been shown to be negatively correlated to the average weight of gray bats (the longer the distance the bat must fly to forage, the less the bat will weigh), lending support to the idea that long flights are energetically costly. Threats The tendency of gray bats to form large colonies made the gray bat especially vulnerable to population decline due to both intentional and unintentional human disturbance. While gray bat habitat locations were always ‘patchy,’ gray bat habitats have become increasingly more isolated and fragmented with human perturbation. Suspected factors contributing to species decline include impoundment of waterways (the creation of dams, which causes flooding in former bat caves), cave commercialization, natural flooding, pesticides, water pollution and siltation, and local deforestation. All North American bat species classified as endangered or threatened by the US. Fish and Wildlife service are cave dwelling species. Of these species, the gray bat congregates in larger numbers at fewer winter hibernacula than any other North