. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. -\ââ âiââ âiââ âiâ'âiâiâr 0 100 200 300 400 500 600 700 Number of Species Figure 37. Number and percentage of non-native and native wetland plant species per growth habit group. (Values at end of bars represent the percentage of non- native species in each habit group.) More than 439 bird species have been documented in Illinois. This discussion will address only the 274 more commonly observed speci
. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. -\ââ âiââ âiââ âiâ'âiâiâr 0 100 200 300 400 500 600 700 Number of Species Figure 37. Number and percentage of non-native and native wetland plant species per growth habit group. (Values at end of bars represent the percentage of non- native species in each habit group.) More than 439 bird species have been documented in Illinois. This discussion will address only the 274 more commonly observed species, including endangered or threatened species (Bohlen 1989) (see Appendix 3). The number of bird species using wetlands may be greater today than in presettlement times. As the land was cultivated and urbanized, those wetlands that were too wet or costly to develop remained as refugia in a disturbed environment. The mobility of birds allows them to exploit many types of habitat to fulfill their physiological requirements. Therefore, any of the 274 bird species listed in Appendix 3 can use wetlands for nesting, foraging, or resting during breeding, migra- tion, or wintering seasons (Figure 41). Of these 274 species, 24 typically depend on wetland habitats for nesting or foraging sites, 81 are strongly associated with wetland habitats during their life cycles, and the remaining 169 use wetlands opportunistically at some time during the year. Other than a study in northeastern Illinois by the Illinois Department of Conservation and aerial invento- ries by the Illinois Natural History Survey, no long-term studies of avian use of wetland habitats have been conducted in Illinois. Studies of this type are difficult because of the dynamic nature of wetland habitats. Wetland characteristics, such as water level and amount of vegetation cover, can change dramati-. Figure 38. Number of non-native wetland plant species found in each Illinois county. cally due to climatic effe
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