Citizen Science: 36th Annual Bald Eagle Survey

Bald Eagle. Photo by Jeff Bryant.

By Roger Digges, CCAS Vice-President

In 1782, the United States Congress adopted the Bald Eagle as our national bird. At that time, an estimated 100,000 pairs of Bald Eagles nested in the area now occupied by the continental United States. But over time, many eagles were shot as predators, their waterways polluted, and the mature trees they nest in cut down. Despite efforts to protect our national bird, when the pesticide DDT came into wide use, eagles ingested it along with their prey, which caused female birds to lay eggs with shells so thin that they were crushed before they hatched. Eventually there were only 417 nesting pairs in the entire contiguous 48 states, just 3 in Illinois.

With the banning of DDT and the protection of rivers and river corridors, today Bald Eagles nest in all of Illinois’s 102 counties. Illinois also plays host to about 3,000 of these magnificent birds, which overwinter in Illinois. We know this, in part, because of the work of hundreds of citizen scientists who have surveyed the birds every winter since 1979, when the National Wildlife Survey conducted the first midwinter eagle survey. The NWS passed the torch to the United States Geological Survey in 1997, and the US Army Corps of Engineers (USACE) accepted the responsibility of coordinating, analyzing, and reporting the survey results in 2007. Here in Illinois, the Illinois Audubon Society recruits volunteers, assigns survey routes, and reports results to USACE.

The Champaign County Audubon Society’s own Helen Parker surveyed the Illinois River from Havana to Beardstown for a number of years until she stepped down after the 2017 survey. My favorite birding partner (also my life partner for going on 48 years) and I have been counting eagles on that route now for the past seven years. During that time, we have found as many as 55 and as few as 9 birds on our surveys.

On a relative balmy Sunday morning, January 7, 2024, Cathy Digges and I set off from Urbana to drive to the beginning of our route at the Havana riverfront on the Illinois River. We were concerned that the warm weather had prevented any ice from forming on the river, which would have concentrated the eagles and make them easier to count. The warm weather would also make roads in certain areas too muddy to get through. December and early January rains may have caused Anderson Lake to overtop the levee we used to drive to a usually quite productive lane along the river.

By this time, we had become veteran eagle surveyors. We knew that the vast majority of white spots in the trees along the river and its backwaters were not the heads of Bald Eagles, but clumps of snow or the scar left by a newly broken branch. We had also learned that finding immature birds, especially on a murky day like this one, against the backdrop of dark tree trunks required both of us scanning the river corridor from one bend to the next, then scanning it again. We had discovered by trial and error that many sections of the river are inaccessible, due lack of roads or presence of private property between us and the river corridor. (Fortunately, state and federal agencies also survey using boats to cover those areas.) We had made a list of where it was possible to access the river and which accesses were the most productive.

We began at the visitors’ center at the north end of Havana, walked out on its dock to scan the trees upstream, drove slowly along Riverside Park and Market Street, and parked in the lot at the end of the park. Eagles were few and far between, but we did see a close flyover.

Leaving Havana, we headed down Illinois 78 for the side channel river access for the tiny community of Bath (population 279). Last year we had found 7 eagles there and heard them vocalizing loudly. This year the riverfront was silent, not an eagle to be heard or seen, until, as we pulled out, an immature bird flew over and perched across the river. Thank you very much.

Northern Harrier. Photo by Jeff Bryant.

We were then off to the Sanganois Fish and Wildlife Area. On the way, we saw flocks of Trumpeter Swans gleaning the fields and a Northern Harrier paralleling our car. The fish and wildlife area was almost completely ice-free, which is rare. On our way towards River Swale, which involves a dicey journey on a one-lane gravel drive with water on both sides, we saw eagles both as we drove in and out. At the swale, we walked the dike until the cold drove us back to our car. Another harrier flew within feet of us along the dike, and far off in the distance, we could make out a brilliant white spot which really was a mature eagle. We took a chance on a muddy road off “the main drag” and were rewarded not only with another eagle, but also our third harrier, as well as a Great Horned Owl in flight.

In Beardstown we had an opportunity to show eagles to a disappointed couple shivering on the riverwalk. Without binoculars (and suitable clothing), they had found no eagles. Within minutes, we glassed both a mature bird and an immature bird. We called them back and gave them a closeup view with our binoculars, the first time the woman had ever seen one.

Heading back to Havana on Illinois 100, we took roads from Frederick and Browning to access points on the river, finding eagles at both. A local man parked at Browning talked to us about the history of flooding on the river. While he was interested in the eagles we were seeing, he seemed to be much more interested in the tow pushing barges past us.

At the Anderson Lake Public Hunting Area, as we drove across the one lane dike between Anderson and Stuckey Lake, we saw a pair of eagles sharing a tree. We expected to see more when we got to the narrow lane between the river and the lake, as we have a few other years. But, alas, no eagles this year. However, on the way out, we found two large flocks of Ruddy Ducks on the lake, one all females or immature, the other all males. Not sure why.

How many eagles did we find? 17 mature birds (white heads, white tails), 6 immature birds, and 1 that it was too hard to tell in the dark overcast. We thought it a good day, considering the mild weather.

This is one of many ways that citizen scientists can help professionals assess the overall health of various bird populations. Watch our newsletter and website for ways you might be able to help.