Bats in Forests: Conservation and Management

4. FORAGING ECOLOGY OF BATS IN FORESTS

FORAGING ECOLOGY OF BATS IN FORESTS Michael J. Lacki, Sybill K. Amelon, and Michael D. Baker 4 Bats have a greater diversity of behavior, diet, and morphology than any other mammalian order. As the primary predators of nocturnal insects, bats play a significant role in all forested ecosystems (Fenton 2003). Despite the importance of bats in forests, the information on foraging behavior for many species in North America is limited. This dearth of information exists because bats are difficult to study and many techniques and methods, developed to assess habitat use and behavior in other mammalian species, are simply not suitable for the study of nocturnal flying mammals (Kunz 1988a). Optimal foraging theory helps explain foraging behavior of animals using mathematical constructs in the context of evolutionary theory (Stephens and Krebs 1986). Optimal foraging theory assumes that “fitness ” (Ehrlich and Holm 1963) is strictly an increasing function of foraging efficiency and that natural selection would, in the long term, lead to the evolution of behaviors that maximize the efficiency at which animals acquire food. A widely accepted measure of efficiency is the rate at which energy is obtained relative to time spent in a particular foraging habitat (Charnov 1976). Presumably, bats allocate considerable time and effort to foraging and likely react to changes in available prey with different strategies for acquiring food (Barclay 1985; Freeman 1979). Experiments and field observations show that bats can discriminate among various habitats and items of food and adjust their behavior to utilize, more-or-less optimally, these varying resources (Barclay 1991; Barclay and Brigham 1994; Norberg 1994). For temperate-zone bats, the need for resources occurs during three critical life-history periods: maternity season, migration, and hibernation . During the maternity and migratory periods, and during winter for some foliage-roosting species, resources include roosting, foraging, drinking, and commuting habitats. It is important to understand not only the habitats that bats use for foraging, but also the components of the area that are significant from the perspective of energy loss or gain by bats (Murray and Kurta 2004). Presently, few studies have examined the influence of required habitats and the spatial arrangement of these habitats on energy balance in bats (Anthony et al. 1981; Salcedo et al. 1995), and none has examined survivorship in forest-dwelling bats. In this chapter, we present an overview of the existing information on the foraging behavior of bats in forests, with an emphasis on North American species,and integrate this information into the context of conservation and management of forest-dwelling bats in North America.We emphasize ecomorphology and echolocation, ontogeny and energetics, feeding ecology and diets of insectivorous bats, and the use of foraging habitat by bats in forests, with attention paid to advancements in field methodology and procedures for data analysis. We close with recommendations for further study aimed at improving both our understanding of the foraging ecology of bats in forests and our capability for managing habitat to ensure long-term conservation of these species. ECOMORPHOLOGY AND ECHOLOCATION ECOMORPHOLOGY Ecomorphology is the study of morphology within the context of its biological role (Karr and James 1975; Swartz and Norberg 1998). Ecomorphology is an area of evolutionary biology separate and distinct from functional morphology in that explanations are hypothetical-deductive as opposed to historical-narrative (Bock 1994). In other words, functional morphology provides measures of physical form that represent adaptations in response to environmental cues over evolutionary time. Ecomorphology incorporates the results of functional morphology into analyses of how physical forms of living organisms help species adapt to their natural environments (Bock 1990, 1994; Winkler 1988). Bats are excellent subjects for ecomorphological studies because of the array of morphological forms they possess in association with their unique mammalian adaptation for nocturnal foraging by flight (Arita and Fenton 1997). A suite of morphological factors influences foraging behavior in insectivorous bats, including body mass and the size and shape of the skull, jaws, and wings. Ecomorphological studies show that the structure of insectivorous bat assemblages is influenced by the correlation between diet and morphology, with morphologically similar species feeding on similar foods (Findley and Black 1983). Among sympatric lasiurines, for example , large bats with large jaws are capable of eating a wider range of prey sizes than small bats, resulting in a broader feeding niche for these bats when food resources are plentiful, although such differences are less apparent when availability of insects is low (Hickey et...