I would take the slight downturn in the mid-winter count of bald eagles in Illinois with a touch of realism. Some routes were not covered. And at least in the Chicago area, eagles are pushing into new territories rapidly, areas not on the routes.
Such as these three (two adults and an immature) on the Southeast Side in late January.
The count breakdown from the Illinois Audubon Society is below.
2009 MID-WINTER BALD EAGLE SURVEY SPRINGFIELD, IL. The number of bald eagles counted during this year's Mid-Winter Bald Eagle Survey was slightly less than last year, but Illinois is just one state participating in this nationwide count. The Survey is conducted at the same time and in the same areas every year to get an idea of the Illinois over-wintering population, and a five-year trend indicates that the bald eagle population is faring well. Surveyors traveled along the Illinois and Mississippi River watersheds, the Ohio River, and Crab Orchard, Carlyle, and Horseshoe Lakes reporting a total of 3,030 bald eagles. Of these, 1821 (60%) were adults, 1134 (37%) were immature birds, and 75 were of undetermined age. Last year 4,292 bald eagles were counted in these areas.
Over the last five Mid-winter Bald Eagle Surveys, 3,324 were counted in 2005, 2,922 in 2006, 1,920 in 2007, and 4,292 in 2008. Most of the eagles that spend the winter in Illinois nest in the northern Great Lakes states and Canada. The open water in our large rivers and available fish make Illinois an important wintering area for the birds.
The Survey was conducted between December 31, 2008 and January 14, with January 9 and 10 as the target dates. Many of the approximately 40 volunteer surveyors are with the Illinois Department of Natural Resources, Illinois Natural History Survey, and the Army Corps of Engineers, but others are simply individuals who volunteer their time to participate. The Great Rivers Chapter of the Illinois Audubon Society takes several routes. An instructor at Principia College takes her class out on a route. Routes range in length from a few miles to over 100 miles and can take from an hour to more than 7 hours to complete. A possible explanation for the 2009 eagle survey decline was that several routes were not covered this year due to lack of volunteers.
Illinois' Mid-Winter Bald Eagle Survey is coordinated by the Illinois Audubon Society and takes place in conjunction with the national survey coordinated by the United States Corps of Engineers. The mission of the Illinois Audubon Society is to promote the perpetuation and appreciation of native plants and animals and the habitats that support them. Illinois Audubon currently owns and manages 12 sanctuaries and wildlife areas, including the Plum Island Bald Eagle Sanctuary at Starved Rock.