. Distribution and abundance of winter populations of bald eagles in Illinois. Bald eagle. February 1988 Havera and Kruse: Winter Populations of Bald Eagles 13 12. Fall arrival and spring departure dates were simi- lar to those observed in the Upper Central Mississippi River Region. The progression to earlier arrival of eagles observed on aerial inventories during fall in recent years also occurred in this region. The highest counts for each year occurred between 11 December and 8 March and the largest number of bald eagles recorded in this region was 527 on 6 January 1986. Immature eagles acc
. Distribution and abundance of winter populations of bald eagles in Illinois. Bald eagle. February 1988 Havera and Kruse: Winter Populations of Bald Eagles 13 12. Fall arrival and spring departure dates were simi- lar to those observed in the Upper Central Mississippi River Region. The progression to earlier arrival of eagles observed on aerial inventories during fall in recent years also occurred in this region. The highest counts for each year occurred between 11 December and 8 March and the largest number of bald eagles recorded in this region was 527 on 6 January 1986. Immature eagles accounted for 0 to of the birds seen on individual flights and an overall average of of the eagles sighted in this region were immatures. Figure 13 depicts the mean number of eagles per inventory counted on individual areas. The largest gatherings of bald eagles within this region occurred at Flat and Swan lakes near the confluence of the Illinois and Mississippi rivers (Fig. 14) and between the towns of Keokuk and Meyer (Fig. 13) on the Mis- sissippi River. The vicinity of Flat and Swan lakes often held more eagles than any other census area in this region (Appendix). Of 127 flights conducted at Flat and Swan lakes, there were only 15 on which no eagles were seen. The highest number of eagles counted at Flat and Swan lakes was 269 (146 adults, 123 immatures) on 6 January 1986, and this was of the birds seen in the entire Lower Central Missis- sippi River Region on that date. The Keokuk vicinity (Fig. 15) hosts what may be the largest concentration of wintering bald eagles found anywhere on the entire Mississippi River. Large numbers of eagles are attracted to the area near Lock and Dam 19 at Keokuk in winter because of the open water below the dam and the readily available supply of fish killed or injured as they pass through turbines of the hydroelectric plant associated with the dam. The main item in the diet of bald eagles wintering in Illinois is fish (South
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