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 in order to forage, the less the bat will weight), lending support to the idea that long flights are energetically costly.
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