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5. IMPORTANCE OF NIGHT ROOSTS TO THE ECOLOGY OF BATS
- Johns Hopkins University Press
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5 A succinct definition of night roosting is “anytime a bat stops flying at night”(S. Cross, pers. comm.). Discerning the role of this behavior in the lives of bats seems fundamental to understanding the life history of these volant, nocturnal organisms, but the difficulty in studying bats roosting at night, especially in forested areas, has discouraged rigorous studies focused solely on night roosting. One does not have to delve far into the literature on bats to realize that the word “roost” often is an accepted synonym for “day roost,” and as a matter of practicality, most information on night roosting has been collected incidental to studies of day roosting in bats (Kunz 1982; Kunz and Lumsden 2003). Much of the information that does exist on night roosting reflects surveillance of individual roost sites and how and when members of a colony use these sites (Anthony et al. 1981; Catto et al. 1995; Swift 1980). Less common are studies using radiotelemetry that focus on individuals and monitor roosting habits relative to nightly activities and areas of use by bats (Audet 1990; Krull et al. 1991; Murray and Kurta 2004). Most studies of night roosting have focused on reproductively active females, whereas data for males and nonreproductive females, and for bats from seasons other than summer, are rare. By default, night roosting includes the tending of young at a maternity roost between foraging bouts, nights when bats elect not to emerge from a day roost because of inclement weather,and the period each night when bats return to the day roost before dawn. Although we acknowledge that these activities constitute night roosting in its strictest sense, our coverage of these behaviors in this chapter is limited. Instead, we emphasize night roosting of bats at sites away from day roosts. Our focus is on forest-dwelling bats in North America, i.e., species that day or night roost in trees or forage in woodlands, although we occasionally include pertinent material on species of bats living in temperate areas of other continents. Additionally, we emphasize studies of bats that used radiotelemetry because of the range in behaviors of individual bats that can be discerned using this approach. In this chapter, we review the functions of night roosts, summarize night-roosting structures and behavior, propose factors that influence night roosting, and describe fidelity to night roosts.We also discuss night roosting and its relationship to the conservation of bats in North AmerIMPORTANCE OF NIGHT ROOSTS TO THE ECOLOGY OF BATS Patricia C. Ormsbee, James D. Kiser, and Stuart I. Perlmeter ica and suggest future research. As Hayes (2003) points out, when we investigate similarities among species in search of underlying patterns, we must remember that each species has a unique natural history and set of behaviors, and decisions by resource managers and conservationists should reflect such uniqueness. This is certainly an admonition worth heeding when evaluating and acting upon information that is available for night roosting. FUNCTIONS OF NIGHT ROOSTS AND NIGHT ROOSTING Numerous physiological, ecological, and behavioral functions have been proposed to explain the behavior of night roosting, ranging from digestion of food, avoidance of predators, and information transfer. There is, however, immense variation in night-roosting behavior, both within and among species of bats, which makes it difficult to identify consistent patterns or even to discern the exact function of a specific night-roosting event. Nevertheless, reviewing proposed functions of night roosts and night roosting provides a biological foundation for our discussion and may help formulate future hypotheses. RESTING Resting seems the most obvious function of night roosting (Kunz 1982; Wilkinson 1992). Nevertheless, it is difficult to identify, let alone quantify , specific resting behaviors, because rest from flight inevitably occurs whenever a bat begins night roosting. Hence, even though a bat might night roost to socialize or to investigate a potential day roost, it also is simultaneously resting from the rigors of flight. There are two general forms of rest,one of which is behavioral and the other physiological. Some inactivity (i.e., night roosting) may occur because the animal has nothing better to do and is equivalent to the “laziness ”of Herbers (1981). This could be a bat that has satisfied its foraging requirements for the night and retires to a night roost,biding its time until it makes a predawn move to a suitable day roost. In this case, resting would be a simple choice between“continue flying for no...