The Illinois chorus frog (Pseudacris illinoensis) and wetland mitigation: What has worked?

The purpose of this project was to examine three mitigation projects designed to produce habitat suitable for the Illinois chorus frog (Pseudacris illinoensis), a state threatened amphibian. The three projects are located in Madison, Morgan, and Cass Counties. There is a need to evaluate these completed projects to determine what the best mitigation strategies are for future mitigation efforts. The Morgan County site, which was the simplest management plan involving only pond construction, was a complete failure. The relatively simple Cass County plan resulted in breeding in 50% of the eight years that surveys have been conducted. Of these years the ponds persisted long enough for transformation in only 50% of these four years. Recruitment occurred in only two (25%) of the eight years that frog activity was monitored at Cass County. The Madison County site had an extensive restoration program conducted including wetland restoration, prairie restoration, hydrologic monitoring prior to pond construction, and extensive post mitigation management (prescribed fires and vegetation reintroductions). Frogs bred successfully at this site in 62.5% of the 16 years post construction. However, froglets and resulting recruitment was estimated at 50% of the years examined including the time period of this study. Thus, the simpler Cass County program and the much more complex Madison County program had roughly equal estimates of success. This assumes that recruitment is the valid measure of success. The two factors that both of these sites share is a good preconstruction survey that yielded an understanding of frog usage at the site and an understanding of the hydrology of the site to allow proper breeding pond construction. Thus, it appears that the keys to successful Illinois chorus frog mitigation are knowing where the frogs are and knowing how deep the ponds need to be to get water levels to last from March to June. Nonetheless, other restoration activities such as wetland restoration and prairie restoration along with public ownership of breeding and nonbreeding habitats may be required for long-term protection of the Illinois chorus frog.