. Distribution and abundance of winter populations of bald eagles in Illinois. Bald eagle. Peak population counts occurred between 3 Janu- ary and 9 March in this region with the highest count of 53 eagles reported on 20 January 1982. Generally, fewer than 25 eagles were seen on each census in this region. Immature birds consisted of 0 to of the eagles observed on individual inventories, and the av- erage proportion of immatures for all eagles seen was The mean number of bald eagles observed per inventory for individual areas is depicted in Figure 19. The downstream portion of thi
. Distribution and abundance of winter populations of bald eagles in Illinois. Bald eagle. Peak population counts occurred between 3 Janu- ary and 9 March in this region with the highest count of 53 eagles reported on 20 January 1982. Generally, fewer than 25 eagles were seen on each census in this region. Immature birds consisted of 0 to of the eagles observed on individual inventories, and the av- erage proportion of immatures for all eagles seen was The mean number of bald eagles observed per inventory for individual areas is depicted in Figure 19. The downstream portion of this region, between La Salle, Illinois, and Spring Valley, Illinois, was gen- erally used the most by eagles (Appendix). The density of bald eagles in the Upper Illinois River Region av- eraged per river mile or per square mile of Fig. nnnilxi ol bald eagles (ounled [)er inventory at census areas within the L pper Illinois River Region. Central Illinois River lief^on. The Central Illinois River Region consists |)rimarily of the Peoria Naviga- tion Pool and extends from near .Spring Valley to Lower Peoria Lake (Fig. 6). This region was inven- toried approximately 125 times between 1972 aii<l 1986. Flights were made during Si-|)iembfi ihroiigh December from 1972 to 1985, during |anuarv from 1973 to I98(), and during February thiough April from 1980 to 1985. Fig. ' number ol the La (iiange Pool of (he Illinois River and stretches lioin Pekin to Naples (Fig. ). I his region has been more t loselv monitored for eagles than anv other with over inventories liom 1972 to 1980. (^c'lisus lliglils \kv\v made fluiing Seplembei lliiough Deteiiibei from 1972 to 1985. during |.iiiuai V lioiii 197!^ Io 198(1. .tnd tlui ing Februarv through .\piil from 1980 to 19M5. Seasonal variation in eagle use ol this region is sliiivMi in Figure 23. No i ensus flights were tonclui led I loin t IV to Icbi I imes
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