With over 1100 species of bats worldwide, the order Chiroptera is the second most multispecied among mammals, accounting for almost one-fourth of all mammalian species. The order is divided into two suborders. The Megachiroptera is a group of just under 200 species, which includes the flying foxes and fruit bats of the Old World. The Microchiroptera with over 900 species includes all the bats of the New World and some Old World species. The two suborders differ in sensory and feeding characteristics. Megachiroptera are fruit- and nectar-feeding bats with a binocular visual pathway and rely on olfaction and vision to find food. Species of Microchiroptera consume a broad range of food including insects, fruit, nectar, small vertebrates, and blood. They have a monocular visual pathway but rely on echoloca-tion to forage and navigate (Simmons and Conway, 2003). Despite the differences between the two suborders, the order Chiroptera is believed to be a single evolutionary lineage, and this monophyly is supported by extensive morphological and molecular evidence (Simmons, 2000).
Chiroptera are incredibly diverse in regards to ecology, behavior, and morphology. Bats can be found on every continent except Antarctica. They inhabit deserts, stone beaches, temperate forests, rainforests, and cities. They roost in caves, under tree bark, in tree hollows, among foliage, under rocks, and in buildings. Behaviorally, several bat species are solitary, others form harems, and
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still others form colonies that can include several millions of individuals.
Body sizes of bats vary from the hog-nosed or bumble bee bat (Craseonycteris thonglangyai), which weighs only 2 g, to the large flying fox (Pteropus vampyrus), weighing in at 1200 g. Their size is probably restricted by flight, as are several other anatomical and physiological traits. For example, females of most species have one reduced ovary and uterine horn likely to reduce body mass for flight (Barclay and Harder, 2003; Jones and MacLarnon, 2001), and juveniles have to achieve almost full adult size before fledging because full bone ossification is necessary to withstand twisting stresses and maintain the wing shape during flight (Barclay, 1994, 1995).
These flight-imposed restrictions translate into very unique life history traits. Mammals can be placed along a continuum of life history traits. At one extreme are small mammals with high metabolic rates, high reproductive rate, rapid maturation, and short lifespan. At the other extreme are typically large mammals with lower metabolic rates and long lifespan, which produce few, large offspring that mature slowly (Read and Harvey, 1989). Bats are paradoxical in that despite being relatively small and having high metabolic rate, they lie on the latter end of the continuum. The majority of species have one offspring per litter, and newborns weigh 15-30% of the body mass of the postpartum mother (Barclay and Harder, 2003; Tuttle and Stevenson, 1982). The gestation period in bats is long, and after birth, offspring take relatively long to reach full adult size (3-4 months in many species; Tuttle and Stevenson, 1982) and typically even longer to achieve sexual maturation (Jones and MacLarnon, 2001). Finally, on average, bats live three times longer than expected based on their body size and metabolic rate (Austad and Fischer, 1991). The oldest longevity record to date is 38 years from a 7-g Brandt's bat (Myotis brandtii). A small sample of bat longevities is listed in Table 36.1, and a more extensive list can be found in the appendix of Wilkinson and South (2001) and in Gaisler et al. (2003). Bat lifespan records come from the fortuitous recapture of wild individuals who were tagged at birth. Therefore, records likely are underestimates of actual maximum longevity (Wilkinson and South, 2002).
Bats have very high metabolic rates and many species are thermolabile. Ultimately, the thermoregulatory strategy of a species is determined by body size, habitat, diet, roosting choice, and social behavior. Because each of these traits varies greatly among species, bats exhibit a broad spectrum of thermoregulatory strategies. Species in the higher latitudes, where temperature varies seasonally, are heterothermic and use hibernation to survive cold winters without food and torpor during the remainder of the year to reduce energy expenditure while roosting. During hibernation, a bat will reduce its body temperature to a few degrees above ambient temperature, and its metabolic rate may drop to one-hundredth of waking rate. The extent of metabolic suppression during torpor
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