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An immature bald eagle was sighted last week at Saganashkee Slough in the Palos forest preserves. Palos is the most likely place in Cook County to find a bald eagle. The forest preserves are big enough to provide them with secluded roosting trees, and the many shallow lakes and sloughs are prime hunting areas for them. The only bald eagles on my own Cook County list are an adult and an immature I saw in the Palos preserves at the Little Red Schoolhouse Nature Center in 1982. If we ever got really lucky and had bald eagles nesting in the county, Palos would almost certainly be the place they would choose.

Bald eagles did nest in Cook County in the distant past. Robert Kennicott, who published an annotated list of our local fauna in 1854, reported the bird as an "occasional resident." A nest was reported in Lake County as late as 1875, and there were nesting eagles in Miller, Indiana, in what is now the west unit of the Indiana Dunes National Lakeshore, as late as 1897.

Contemporary sources blame indiscriminate shooting for the extirpation of our local population. The shooting was, of course, supplemented by the flood of humans who moved to the southern end of Lake Michigan in the past 150 years. Bald eagles nest along the shore of Lake Michigan and the other Great Lakes wherever there is sufficient solitude and a few big trees. The dramatic loss of shoreline habitat would probably have done them in even without the shooting.

Elsewhere in Illinois bald eagles were easy to find. Robert Ridgway, writing in 1889, reported that "along all the larger water-courses in our State the Bald Eagle is a more or less common bird, and may be met with at all times of the year." They stayed fairly easy to find until the late 40s, when DDT began to take its toll.

Birders can get wildly excited about seeing nondescript little brown birds. If a Brewer's sparrow showed up in Chicago, people would drive hundreds of miles for a look at it, yet no one who wasn't deeply involved with bird-watching would be the least bit interested. But bald eagles are easy to appreciate. Any bird with an eight-foot wingspan commands attention, and that fierce raptorial beak adds to the overall impression.

Its regal demeanor had a lot to do with its selection as our national bird, but there have always been people around who did not admire the bird's character. Most people are familiar with Ben Franklin's tongue-in-cheek recommendation of the wild turkey as a more suitable symbol. A.C. Bent, writing in Life Histories of North American Birds of Prey, said of the bald eagle: "Its carrion-feeding habits, its timid and cowardly behavior, and its predatory attacks on the smaller and weaker osprey hardly inspire respect."

Of course you could argue that attacks on the small and weak are just the sort of things regal types do best. The relationship between the bald eagle and the osprey is the perfect paradigm for our relationship to the Sioux or the Nicaraguans. Eagles watch ospreys. And when an osprey catches a fish, an eagle will attack it and force it to drop its meal--which the eagle will then snatch out of the air.

The charge of timid and cowardly behavior is a reference to the way bald eagles desert their nests if an intruder gets too close. The adults fly off and just wait for the intruder to leave. This is quite different from the actions of, say, the great horned owl, which will even attack something as large as a human being if it gets too close to an occupied nest.

Carrion eating has long been a despised habit. We put a very high value on murder, so we admire animals that kill to eat and have nothing but contempt for those who eat things that are already dead. Of course our attitude changes if a predator is killing animals we want for ourselves. That we don't like.

Actually bald eagles are extremely opportunistic in their feeding habits. They do fish for themselves. They hover over the water just as ospreys do and dive on anything they see. They also are very effective hunters of waterfowl. An eagle will swoop low over a flock of ducks or coots, terrifying them into flight. If one bird becomes separated from the flock, the eagle immediately concentrates on it, sometimes overtaking it in flight, sometimes hovering overhead until the prey has exhausted itself with repeated attempts to escape by diving.

Even Canada geese are vulnerable to a hunting bald eagle. The eagle may not be able to fly while carrying something as heavy as a goose, so it will swim, dragging its catch through the water to shore. Eagles have been seen swimming as far as half a mile dragging a goose behind them.

Eagles often spend the winter around waterfowl refuges, and they concentrate especially on wounded or injured birds. Some eagles have gotten lead poisoning from eating ducks with lead shot imbedded in their bodies.

Eagles also take mammals as large as fawns. There are reports of eagles with mule deer remains in their stomachs, but it could be that they simply found the animals dead.

If eagles are rearing young, they bring their catch to the nest. The amount of food a pair can accumulate is amazing. Some nests are heaped with the remains of ducks, grebes, small herons, miscellaneous mammals, and fish weighing as much as 15 pounds.

Guns started the decline of the bald eagle in North America. Farmers believed that eagles killed lambs, chickens, and other domestic stock. And a lot of people shot them just for fun. As recently as ten years ago illegal shooting was the largest single known cause of death among bald eagles, although the prevalence of shooting had declined during the 70s.

DDT hit them in subtler ways. Most people are familiar with the fact that birds that ingest large amounts of DDT lay eggs with very thin shells. The shells are too weak to hold up during incubation, so no live young are produced. It has been discovered that DDT interferes with the production of estrogen in female birds. Estrogen controls the accumulation of calcium for eggshells. (Estrogen also plays a role in calcium metabolism in human females.)

When animals ingest DDT, it builds up in their bodies. As you move up the food chain, quantities of DDT multiply dramatically. By the time you reach a large, long-lived animal feeding at the top of the food chain--a bald eagle, for example--the pesticide is present in large enough amounts to do real damage.

Reproductive failure is a very sneaky problem. Bald eagles live a long time, and they reproduce slowly. They don't start nesting until they are four or five, and a pair is unlikely to produce more than two or three young a year. So the effects of reproductive failure are not immediately noticeable. There are still lots of birds around. The decline becomes obvious only when the current generations of adults begin to die with no young birds around to replace them.

However, birders began to realize we had a problem in the early 50s. Young bald eagles are more or less brown all over. They don't develop the distinctive white head and tail until age four. So people who really pay attention to birds and who keep records of what they see would notice quite early that they were seeing too many adults and not enough young.

By the early 70s only two populations of bald eagles remained in the lower 48 states: a sedentary flock in Florida and a migratory population in the upper midwest. Since DDT was banned in 1973, the birds have been making a comeback. There are more of them in the Rockies now, and the upper midwest population is growing. Many of the birds that nest in Minnesota, Wisconsin, and Michigan winter in Illinois. They gather around the dams on the Mississippi and Illinois rivers where the water remains ice free. Some of these birds began to stay through the summer in the late 70s. In 1982 Jo Daviess County in the northwestern corner of the state was the site of the first known nesting in the state since 1943. Since then, successful nesting has taken place at Crab Orchard National Wildlife Refuge and Horseshoe Lake, both at the southern end of the state.

Bald eagles are tolerant of the presence of humans. In Florida they have been known to nest in tall pines on golf courses. With luck we might soon have a nesting pair somewhere in the Chicago area.

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