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January 1999
Driving over the bridge in Lisbon Falls at the end of a day, I saw a mature bald eagle on the rocks below. I pulled over and stood looking down river. The eagle was skimming the water, gliding directly away from me. By a trick of the light, the dark body was invisible and appeared like a tear in the fabric of the universe. I could see only the white of the tail and the head, gleaming. A van pulled up, and a woman joined me to watch. The eagle passed beyond the bend in the river, and we headed back to our vehicles.
“Pretty neat to see that on the way home from work!” I exclaimed. She looked at me quizzically. I wondered if she knows what precious neighbors we have in the bald eagles.
While no longer considered endangered in Maine, the bald eagle remains on the threatened species list here. According to the Maine Department of Inland Fisheries and Wildlife, there has been growth and range expansion of the breeding population. They count occupied nest sites, nesting pairs, and the young that fledge from each nest. Over time, the records give an ambivalent picture of the situation. In 1998, for example, there was a decline of nesting pairs unprecedented in the last 25 years, but the rate of nesting success showed some improvement compared to a very low rate the previous year.
The poor nesting success may be the lingering effects of now illegal environmental contaminants that have influenced the recovery of eagles in Maine for the last fifty years. These chemicals break down very, very slowly and continue to accumulate in the eagles through their food sources. Heavy metals, especially the neurotoxin mercury, also cause problems for eagles as well as for other species such as loons.
Adult survivorship is becoming an issue in Maine. Twenty-five adult eagles were discovered dead or seriously injured from impact and human-related causes in 1996. In 1997 three eagles were killed by cars, demonstrating the problems eagles face in populated areas. Because of nesting failures and deaths of adult eagles, there is concern for their long-term welfare.
In our area, bald eagles nest around Merrymeeting Bay and at a few places on the Androscoggin River. They hunt up and down the river valley. I most often see them along the river on Lincoln St. in Lewiston and Riverside Drive in Auburn. These birds are big. They are about thirty inches from head to tail, and their wingspan ranges from six to seven and a half feet. Young birds are blackish, with motley and irregular white patches. It’s a treat to see a mature one, of three or more years, with the dazzling white head and tail, and heavy yellow bill. These white markings reassure me I am making a correct identification. Sometimes when circling low, the birds loom so large, I know they are eagles no matter what their markings.
They build their nests in forks of large living trees, thirty to sixty feet high, in open areas on rivers, large lakes, marsh or along the seacoast. Occasionally they may nest on a cliff. The nest is a platform made of large sticks well lined with fine materials. They favor areas with an unobstructed view and, if the habitat is rich enough in food, in proximity to other nesting eagles. Old nesting territories and traditional nest sites are used by successive generations of eagles.
An eagle in the wild can live twenty years. For breeding, a male and female eagle pair will have a long-term bond. They build the nest and rear the young together. They have one brood each year, with one to three eggs, but usually two. The larger chick often kills the smaller chick. This seems to occur even when food supplies are abundant. Rather than an effort to produce more than one offspring each season, experts think this may be an adaptation where the second egg is like insurance in case the first egg is lost from infertility, predation or damage.
If the habitat provides it, fish are the bald eagles’ staple diet. They snatch the fish from the water’s surface with their talons. They also prey on smallish mammals, such as rabbits. A sign that the fisheries are depleted is that eagles now commonly hunt cormorants, gulls and ducks. While hunting, eagles use snags as perches. Once an eagle finds a successful hunting spot, it returns to it regularly.
In the winter, eagles congregate at feeding areas and night roosts. They tend to locate near the coast and inland where water is free of ice so they can fish. The warm waters in the river near the Lewiston Pollution Prevention Plant provide open water when all else is frozen. The gulls and ducks feeding there in the nutrient-rich waters may attract the eagles. In ice-bound areas, eagles feed on carrion such as deer carcasses.
During breeding, eagles are very sensitive to disturbance from humans, and there are restrictions on activities near their nests. But winter stresses, such as the need for food, seem to raise the eagles’ tolerance of human activity. Sure enough, that is when I usually see them near the cities, on my way to or from work. When I see a bald eagle circling just overhead or perched in a snag between the road and the river, great nature is my companion. The day has lost all sense of the mundane and I’m on an adventure.
By Nancy Coverstone (ncstone@umext.maine.edu), University of Maine Extension Educator in Androscoggin and Sagadahoc Counties
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