The abundance of each species at each site varied each year during the study (Fig. 3). Amphibians significantly increased at Kankakee Sands from 1998-2003 (Table 1). The number of sites with breeding amphibians increased more than six-fold and the total number of populations increased by more than an order of magnitude since restoration activities began in 1999 (Table 1). Relative abundance index scores significantly increased from a total of 30 in 1998 to 453 in 2003 (r2 = 0.968, P = 0.003) and the mean relative abundance index score per population significantly increased from 2.14 in 1998 to 2.63 in 2003 (t = 14.617, df = 3, P = 0.001). All seven species that were present in 1998 became significantly more common since habitat restoration began in 1999 and breeding activities spread into every land management unit by 2003 (Table 1). Three species colonized restored habitats at Kankakee Sands: the American Bullfrog (Rana catesbieana) colonized between 2001 and 2002, and the Cope’s Gray Treefrog (Hyla chrysoscelis) and the Tiger Salamander colonized between 2002 and 2003. The mean species richness per breeding site increased significantly from 2.0 in 1998 to 3.9 in 2003 (F = 7.979, df = 1, 41, P = 0.007). A linear regression model best explained the increase in the percentage of management units with breeding populations of amphibians, species richness, and the mean species richness per breeding sites (Table 1). An exponential growth regression model best explained the increase in the number of amphibian breeding sites and total number of amphibian populations (Table 1).
The species with the greatest rate of increase between 1998 and 2000 were American Toads (Bufo americanus), Western Chorus Frogs and Spring Peepers (Pseudacris crucifer; Table 1). The species with the greatest rate of increase between 2000 and 2001 were Eastern Gray Treefrogs (Hyla versicolor) and Green Frogs (Rana clamitans). Fowler’s Toads (B. fowlerii), Bullfrogs, and Northern Leopard Frogs had the greatest rate of increase between 2001 and 2002. Western Chorus Frogs, Spring Peepers, and American Toads had the greatest increases between 2002 and 2003. Overall, Western Chorus Frogs, Spring Peepers, Northern Leopard Frogs and Fowler’s Toads had the greatest increases during the survey period. A linear regression model best explained the increase in the number of breeding populations of American Toads, and an exponential growth regression model best explained the increase in the number of breeding populations of Fowler’s Toads, Eastern Gray Treefrogs, Spring Peepers, Western Chorus Frogs, Green Frogs, and Northern Leopard Frogs (Table 1).
The first areas of colonization and the greatest increases in the number of breeding populations were in the southwestern units (Fig. 3; sites J, K, L) adjacent to Willow Slough (χ2 = 53.22, df = 2, P
During 2001, we captured 54 adult and 60 metamorphosed juvenile frogs; whereas, during 2002 we captured 60 adult and 1234 metamorphosed juvenile frogs. All of the species identified in the call surveys were also observed during searches or in traps. However two species were dominant. More than half the adults found in terrestrial searches and traps were Fowler’s Toads and 90% of the juveniles found in terrestrial searches and traps were Northern Leopard Frogs. In 2001, tadpoles were observed in the restored wetlands. Although some tadpoles survived to metamorphosis, many died when the wetlands dried in late spring 2001 (Fig. 4). Spring rains during 2002 flooded many of the wetlands, including drainage ditch remnants. Although many of the wetlands began drying in June, most tadpoles survived through metamorphosis in deep remnant ditches (Fig. 5).
However, we observed minnows (cyprinids) and sunfish (centrarchids) in these ditches. We found tadpoles and metamorphosed juveniles at all of the wetlands where frog calls were heard in 2002 and 2003. Tadpoles of Northern Leopard Frogs and toads (Bufo sp.) were the most abundant amphibian larvae observed in restored wetlands, but tadpoles of Spring Peepers, Chorus Frogs, Green Frogs, American Bullfrogs and treefrog (Hyla sp.) and Tiger Salamander larvae were also observed. Wetland depth changed rapidly during all years. Many wetlands
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