Abstract
Many amphibian populations appear to be declining throughout much of the world (Corn and Fogleman 1984, Beiswenger 1986, McAllister and Leonard 1990, Wake and Morowitz 1990, Wake 1991). Declines appear to be particularly noticeable in the western United States in the true frogs and toads (families Ranidae and Bufonidae, respectively). For example, leopard frogs (Rana pipiens) and western toads (Bufo boreas) have disappeared from the majority of their historic ranges in Colorado (Corn et al. 1989) and populations of spotted frogs (Rana pretiosa) have gone extinct or declined on the periphery of their range in Washington, Oregon, California, Nevada, and Utah (McAllister and Leonard 1990). Monitoring amphibian populations is important for several reasons. First and most obvious, we need to know if and why amphibian populations are fluctuating so we can effectively manage and preserve them. Second, amphibians are important components of many ecosystems, both as predators and prey, often making up a significant amount of a system's biomass (Pough 1983). Finally, amphibians are potentially sensitive indicators of environmental change because of a unique combination of biological characteristics such as their permeable skins, biphasic life cycles, and aquatic reproduction and development (Wake and Morowitz 1990). For these reasons, the monitoring of amphibians populations has been recommended as an "early warning system" of environmental change (Beiswenger 1986, 1988, Wake 1991).