Friday, April 13, 2007

Illinois Chorus Frogs


The bell-like whistles of Illinois chorus frogs resemble the high pitched "preeps" of spring peepers so dramatically that I listened to recordings of both calls, one after another, about thirty times. The difference is clear now: peepers have a slight rise in pitch at the end of the calling note. Since the breeding period began, I have heard a single ICF call. My turtle surveyor, Brad (who furnished the great picture), has heard them in chorus and seen them on several occasions this spring. He's marked the locations and even checked for tadpoles following calling events. I have no excuse not to have seen them but that every rain event seems to occur when I'm in the Ozarks.

The small, 1-1 1/2 inch warty frogs are listed as rare by the Missouri Dept. of Conservation, but the U.S. Fish and Wildlife Service is trying to list the frog as endangered. The only known, disjunct populations are in southeast Missouri, northern Arkansas and southern Illinois. ICFs are one of the few animals who have adapted to the many landscape changes that have occurred in the past 100 years. They used to live in sand prairie wetlands, but with most sand prairie now in cotton and soybean cultivation, ICFs have managed to survive in the agricultural ditches and cultivated fields.

Research in the past 5 years has unveiled not only the soil types the frogs live in, but that the frogs are responsible for keeping boll weevil populations in check. ICFs are fossorial but emerge from the sand to breed in the early spring and, on occasion, to feed during heavy summer rain events. They only live in certain sand series: Clana-Malden, Crevasse-Canalou, Clana-Canalou and so on. Aside from cultivated fields and ditches, the frogs live in the sandflats of Crowley's Ridge and in historic sand prairie territory of Scott, Dunklin and Mississippi Counties. Suitable breeding habitats (herbaceous wetlands) are rare, but when the frogs are present, they tend to be locally abundant.

Cotton pesticides and defoliants (heptachlor epoxide and DDE) have been found in high concentrations in Scott Co. frogs. The Clean Water Act only protects isolated pools if the continued existence of the rare or endangered animal is threatened. In Missouri, when ICF populations are located, the state herpetologist steps in to protect them. Traditionally, he alerts the landowner of the rare frog population. Natural history of the animal is explained and the landowner is encouraged to continue the current management practices (if the wetland provides enough habitat for the frog), or is referred to an NRCS wetland biologist to transform part of the property into a viable wetland. In the past 6 years, thousands of Wetland Reserve Program dollars, set aside by the Farm Bill to encourage wildlife conservation projects, have been spent to establish appropriate breeding grounds for the ICFs.

Agricultural habitats are not optimum for these animals. Nevertheless, despite all the odds, they continue to thrive in southeast Missouri, whistling in the warm spring nights just as they did in the sand prairies.

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