. use for a given area. The number of inventories and the mean number of eagles observed per inventorv were based on the period between the first sighting of a bald eagle in the fall of each year and the last eagle sighting the following spring, and not the entire census period from fall through spring. This proce- dure appropriately concentrated on the period when eagles were present in the various regions. The arrival and departure dates of bald eagles in Illinois vary each year as a result of differences in weather, freeze- ups, and other unpredictable phenomena of nature. Differences in th
. use for a given area. The number of inventories and the mean number of eagles observed per inventorv were based on the period between the first sighting of a bald eagle in the fall of each year and the last eagle sighting the following spring, and not the entire census period from fall through spring. This proce- dure appropriately concentrated on the period when eagles were present in the various regions. The arrival and departure dates of bald eagles in Illinois vary each year as a result of differences in weather, freeze- ups, and other unpredictable phenomena of nature. Differences in the length of the inventory period and the number of years of censuses should be taken into consideration when making comparisons in values for the mean number of eagles coimted per inventory among regions (Table 4). For instance, the Upper Mississippi River Region was inventoried din- ing 1980-1983 as compared with 1972-1986 for the other Mississippi River regions. Bald eagles ha\e gen- erally increased in Illinois since 1972 (Table 3) and a mean value for the number seen per inventory in more recent years (1980-1983) mav pn)vide a differ- ent value than a mean calculated on data from 1972- Table 5. â River miles and wet and area inch ded in riverine census regions. R vcr Mile ,;j Wetland Area'' Region mi^ km- Upper Mississippi River Upper Central Mississippi Ri\e i;n.:i LowerC'entral Mississippi Rive Lower Mississippi River Upper Illinois River Central Illinois River Lower Illinois River Lower Kaskaskia River :«).o Tig. ol llliiHiis inventoried lot bald In the lllii Natuial HiMnn Sui\<\. 1972-1987. â¢' .Army Corps of Fngineers (1978). Illinois Division of W atcr- wavs (I9(=i9). '' et al. (1977). Haveia (1985).
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Keywords: ., bo, bookcentury1900, bookcollectionbiodiversity, bookleafnumber18
