. The Changing Illinois environment : critical trends : summary report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. 50 • The Changing Illinois Environment Some wetland bird species appear to be increasing in number. • Combined popula- tions of migrating double-crested cormorants In the Illinois and Mississippi valleys rose from fewer than 100 birds around 1970 to nearly 6,000 in 1992. Page 50 Figure 7-4 Bald Eagles Along Major Illinois Waterways 1958-1993* 600 500 - Many nesting birds such as egrets, herons, and do
. The Changing Illinois environment : critical trends : summary report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. 50 • The Changing Illinois Environment Some wetland bird species appear to be increasing in number. • Combined popula- tions of migrating double-crested cormorants In the Illinois and Mississippi valleys rose from fewer than 100 birds around 1970 to nearly 6,000 in 1992. Page 50 Figure 7-4 Bald Eagles Along Major Illinois Waterways 1958-1993* 600 500 - Many nesting birds such as egrets, herons, and double-crested cormorants build colonics in wetlands (mainly floodplain forests). The total numbers of some birds, such as great egrets, increased during the 1980s, while those of the night heron declined. Fluctuations in colony size and species composition are common among such birds: how- ever, the apparent increased number of colonies may be partly the result of more diligent field surveys. Of the 43 bird species listed as endangered or threatened in Illinois as of 1993, 30 are strongly associated with wetlands, especially during the breeding season. Some species are dependent on more than one type of wetland; the great egret, for example, typically nests in floodplain forests but prefers to forage in shallow-water wetlands. As recently as the 1880s, many bald eagles nested in Illinois, mainly along the lUmois and Mississippi rivers. However, poisoning by the insecticide DDT, hunting, and habitat destruction throughout its range caused a decline in eagle populations, and from 19~8 to 198" only two to four such nests were recorded in Illinois. While numbers of nesting bald eagles seem to be increasing in recent years—17 nests were recorded in 1992—Illinois remains mamly a winter- ing ground. A total of 1,21 1 bald eagles were counted along the Illinois and Mississippi rivers in \^^0. (Figure 7-4) The doublc-crcstcd cormorant is another bird that seems to be rebound
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