Amphibians include 2 major groups: the salamanders (Salientia--7 species in Wisconsin), which have tails and generally travel by walking or creeping; and the frogs and toads (Anura--12 species in Wisconsin), which as adults are tailless and travel by hopping. With some notable exceptions, both groups pass their larval stage as gilled tadpoles in aquatic habitats of various sorts. Salamander larvae tend to be carnivorous while anuran larvae tend to be herbivorous; as adults, both groups feed primarily on insects and other small invertebrates.
Most Wisconsin anurans emerge from their natal wetlands as they metamorphose to adult form, and spend most of their adult life on land. Some, such as the green frog, mink frog, and bullfrog, rarely leave water. All Wisconsin anurans return to the water to breed during fairly well-defined breeding seasons, which may begin while snow is still on the gound, or as late as early summer, depending on the species. Early breeders tend to lay their eggs in temporary ponds where predators such as fish cannot survive. These tadpoles must grow quickly so they can metamorphose before ponds dry up in late summer. Late breeders, like the Green Frog, lay their eggs in permanent water, and tadpoles may not metamorphose until the second year. At breeding sites, male frogs and toads advertize their presence with distinctive calls.
Recent, possibly widespread declines in amphibian populations (Blaustein and Wake 1990) are disturbing because of the important roles of amphibians in many ecosystems. Moreover, their complex life cycles, insectivorous habits, permeable skin, and sensitivity to water chemistry in the egg and larval stages probably make them good bioindicators of environmental stress. There is little geographic or taxonomic pattern to the reported declines, some of which are from sites free of local anthropogenic disturbance. Causes for decline are usually unknown, and may be various, including habitat destruction, chemical contamination, introduction of predators, global climatic changes, acidic precipitation, or synergistic combinations of these factors (Blaustein and Wake 1990, Phillips 1990, Wyman 1990). Recent discoveries of malformed anurans, including at least 7 species in 41 Wisconsin counties (Hay, unpublished report), has heightened concern over amphibian populations.
Determining the nature, extent, and causes of amphibian population declines is hampered by a dearth of long-term population data. In fact, many reported declines were based on local, short-term, or anecdotal evidence and may or may not reflect important or widespread problems. There is clearly a need for a coordinated system of research and monitoring that will determine and characterize significant population trends and identify causes (Blaustein and Wake 1990, Pechmann et al. 1991). This includes long-term population monitoring for a large number of species over wide areas that will identify changes in geographic ranges and distinguish regional and long-term trends from those that are local or short-term. Such a monitoring system could alert researchers and managers to species and regions in need of attention, and suggest patterns or causes of declines. The North American Amphibian Monitoring Program (NAAMP) was initiated in 1994 to investigate monitoring needs and methodologies, and suggest standards. For anurans, which advertise their presence during the breeding season with species-specific vocalizations, volunteer-based auditory surveys were recommended by the NAAMP as the best monitoring method for most of the continent. The suggested methodology is based on the long-running Wisconsin Frog and Toad Survey.