The Distribution of Habitat of the Pickerel Frog in Wisconsin
Johnson, Michael J.
University of Wisconsin-Stevens Point, College of Natural Resources
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The distribution, habitat and breeding behavior of the pickerel frog (Rana palustris), a Wisconsin Threatened Species, was investigated during the period May 1980 through November 1981. Pickerel frogs were identified at 61 Wisconsin locations in 19 counties; 91% of these sites were in southern or southwestern Wisconsin regions containing many spring streams. Chemical analyses of 52 water samples, collected at 38 sites where pickerel frogs were found, indicated they bred and existed in or near waters that varied widely in water quality. Water temperatures recorded at summer sites where pickerel frogs were found, although mostly cool (range: 18-21.5 C), were not significantly different from water temperatures measured at similar sites where pickerel frogs were not found. Pickerel frogs were associated with both canopied areas and shrubby wet meadows with spring-fed stream$ during this study. The presence of dense vegetation in both of these areas was important for frogs inhabiting these areas. Land use practices did not influence pickerel frog occurrence with the exception of plowed fields which reduced ground cover and possibly insect biomass; only 4 of 52 sites were associated with this land use practice. Twenty-three pickerel frogs were fitted with radio transmitters and monitored from 15 April - 1 November 1981; data from 12 of these frogs were used to determine habitat preferences. Once they had migrated from the breeding areas pickerel frogs remained mostly sedentary and were located in or near the streams significantly more times than expected by chance alone during both the spring and summer periods. Pickerel frog breeding behavior was monitored at 2 sites during 1981. Breeding calls were first heard on 7 April and lasted through 1 June of 1981. Average water and air temperatures recorded while pickerel frogs were calling were 18.6 C and 14.6 C, respectively. Pickerel frog egg masses were attached to submergent vegetation in shallow, sluggish waters, and concentrated where they would receive the greatest amount of sunlight allowing for faster and longer warming and accelerated rate of development. Pickerel frog egg masses all hatched within 24 days with tadpoles metamorphosing 75 days after first hatching. Size of local breeding populations were estimated from adult pickerel frogs captured at both breeding sites. Males appeared to outnumber females at these sites, however, the higher capture of males may be attributed to their more conspicuous breeding behavior. Pickerel frogs and leopard frogs were rarely found in the same areas, habitat separation would reduce competition for the same food source.