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Last weekend the Chicago Rare Bird Alert reported three sightings of bald eagles in the Chicago area--one near Waukegan, one in Du Page County, and one at Palos, where four birds were seen. These may not seem like large numbers, but the four birds sighted at Palos tied the one-day high count for the Chicago region.

Bald eagle sightings have been becoming somewhat more common around Chicago in recent years--a reflection of the bird's improving fortunes. Bald eagle populations are still alarmingly low, and the threats they face could still do them in. But they are certainly better off than they were when DDT was regarded as the answer to everything from head lice to the boll weevil.

The story of DDT and birds of prey is well known, of course. Birders were the first to notice that raptor numbers were dropping, and they were the first to suspect that DDT was implicated in some way. The birds were laying eggs with very thin shells, shells so thin they usually broke before the young could hatch. A long, complex piece of scientific detection eventually established that DDT--or DDE, a breakdown product--interfered with the production of a hormone that regulated calcium metabolism in ovulating female birds. Bald eagles bounced back when DDT was banned, and they began to enjoy an unprecedented flow of esteem and concern from people.

Our assault on the environment had become so deadly that the national symbol was about to be driven to extinction. The plight of the bald eagle became a focal point for environmental action. A birder and auto-parts dealer from East Moline, Illinois, named Elton Fawks began a winter eagle census in the early 70s. Working with a few friends, he counted birds along the Mississippi near his home. His idea caught on and within a decade, the count encompassed almost the entire Mississippi valley, and the Ohio, Wisconsin, Illinois, and Missouri rivers as well.

The data from a winter census can be tricky. Are there really more birds, or just more counters? Are there really more birds, or just more within the range of the count?

While their usefulness to science may be limited, the winter counts definitely got a lot of people involved with eagles, and those people generated a ton of publicity for bald eagle preservation. In Illinois, where a substantial number of eagles spend the winter, protection of winter roosts has become a conservation cause that can count on widespread support. The U.S. Fish and Wildlife Service, the Illinois Department of Conservation, and the Nature Conservancy are a involved in winter eagle protection.

Presumably, the bald eagle was selected as our national bird because it is an eagle--a traditional symbol of power--that lives only in North America (except for a few that have slipped across the Bering Strait into Asia). It is certainly a gorgeous bird. The solid white head, the golden yellow beak, and the flaring white tail make a great Great Seal. By the way, bald meant "white headed" as well as "hairless" in the 18th century.

From the earliest days of the Republic, some have complained that by choosing the bald eagle we showed ourselves more interested in a pretty face than in good character. Ben Franklin made a mocking suggestion that we should have adopted the turkey instead. The rap against the bald eagle is summarized by Arthur Cleveland Bent in Life Histories of North American Birds of Prey. "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 say that this is the perfect bird for the country that backed the contras, but Bent went on to complain that the bald eagle did not "exemplify the best in American character."

Why is it that so many people admire pure predators like the golden eagle? We admire animals that make a living by plunging their razor-sharp talons into the tender flesh of helpless, bleating fawns and terror-stricken bunny rabbits, and we despise carrion eaters that get what they need without causing pain to any other creature and that perform a vital service for the community in the process.

We could arrange America's three largest birds of prey on a continuum, with the golden eagle at one end as the predator, the turkey vulture at the other end as the pure scavenger, and the bald eagle in the middle as a little of both.

We could also make a physical series according to the principles of Sullivan's Law of Beaks and Feet. The golden eagle has the most powerful talons of the three, because its feet are its principal weapons. Its beak is relatively small; it only has to tear up animals that are small enough for the talons to capture. Turkey vultures have weak feet and huge beaks. They don't kill anything. If they need to hold something down, they just stand on it. But their beaks are strong enough to pull apart the corpses of big animals--bison and elk, for example.

Bald eagles are again in the middle. Their talons are strong enough for some hunting, and their beaks are big enough for some carrion eating. They are mainly fish eaters. They may catch them live, pick up corpses that have washed ashore, or steal them from an osprey by terrorizing the smaller bird into dropping its catch. Bald eagles are also fond of waterfowl. They specialize in the sick and injured, because weakened birds are easier to catch. An eagle will fly low over a flock of ducks or coots sitting on the water and watch how the individual birds react. Most will fly away or dive quickly, but if one of the flock reveals a weakness, the eagle will single it out and harass it until it is too exhausted to flee. Eagles are also capable of very active hunting. They have even been seen capturing waterfowl on the wing.

Bald eagles build the biggest nests known among the world's birds. (To be exact, I should say the biggest nests used by a single pair.) They erect an enormous platform of sticks, usually at the top of a tall tree, and line it with softer materials. One nest found in Florida was 15 feet deep and 8 feet across, although 10 by 6 would be a more typical measurement. Pairs will use a nest for several years, generally replacing the top layer of stuff at the beginning of each season.

Bald eagles lay small eggs for such a large bird. A female weighing up to 14 pounds produces an egg only a few millimeters longer than the egg of a three-pound chicken. The eggs must be incubated for 35 days, and the young remain in the nest for nearly three months after hatching. After they leave the nest, they stay nearby and still depend on their parents to feed them. Two eggs is a typical clutch.

Almost any place with tall trees, water, and a bit of solitude can become the site of a bald eagle's nest. They once nested over much of the continent, including the Chicago area. Our last reported nest was found near what is now Gary in 1897. DDT wiped out many populations. The birds survived only in Florida, the Pacific Northwest, and the upper Great Lakes. These are still the centers of abundance. Thomas Dunstan, a professor of biological science at Western Illinois University, is part of a group of scientists who have been collecting nesting information from Minnesota, Wisconsin, and Michigan for more than a decade. "We are seeing nice increases in nesting populations," Dunstan told me, "and the trend extends over a large area. Areas where eagles lived before DDT are now being reoccupied."

The importance of the breeding range is obvious enough, especially for a bird that defends a nesting territory of several square miles. They need space up on their northern breeding grounds in the spring and summer even more than they need it here in winter. Wintering bald eagles gather around likely food sources in flocks, and become quite tolerant of each other. If there is enough food, they don't need a lot of room.

Another encouraging trend is toward an expansion of the breeding range. Birds have been attempting to nest along the Mississippi in Illinois for several years, and this year the state had ten territorial pairs. Four pairs produced young. Two nests at Crab Orchard National Wildlife Refuge near Carbondale fledged five young. A nest at Spring Lake National Wildlife Refuge on the Illinois River produced two young, and a nest at the Savanna Army Depot on the Mississippi just south of Galena produced one fledgling. Breeding attempts are also increasing in Ohio and along the lower Mississippi.

The one region to which the eagles have not returned is New England, where DDT wiped them out. There just hasn't been time for immigrants to reoccupy the region. If any try, they will have to pick their nesting ground with great care. Acid rain is turning many lakes in New England into lifeless water tanks. A fish-eating bird will find nothing to live on. As the effects of acid rain accumulate, eagles may lose nesting grounds in the upper midwest, too. We almost knocked the eagle off the top of the food chain with DDT. That stuff was insidious because it accumulated in animals. Copepods eating plankton absorbed small amounts of DDT. Fish eating copepods got a small dose with each meal, and bald eagles eating fish got a large dose with each meal. It wasn't until the poison got to the top spot on the food chain that it accumulated enough strength to do harm. Acid rain is a very unsubtle approach, a scorched-earth policy. It completely destroys the aquatic food chain, killing off plankton, copepods, and fish--leaving eagles absolutely nothing to eat. Starvation is a quicker route to extinction than thin eggshells.

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