As the non-Winter closes, we should take a moment to ponder how it might have affected and continues to affect our native birds. This winter I noticed many eagles, both adults and immature, were still seen locally in January and February, 2024 when, in past years, the birds had migrated out of the area. We had an adult and an immature patrolling a stretch of Lake Superior’s South Shore, and also observed an adult pair spiraling together over the Keweenaw Peninsula. We know that Bald Eagles will not always migrate south in fall or early winter, but most do. Birds do not undertake the perilous task of migration if they have an ample supply of food. The eagles’ diet of fish, and carrion suggests that if there is open water, or road-kill, the big birds might not migrate.
Bald Eagles are classed taxonomically as “Sea Eagles”; North American Bald Eagles form a “species pair” with the Eurasian White-tailed Eagle, which resembles the bald, except for the head, which is brown, not white. Taken collectively, the two species span the Northern Hemisphere, though not always in great numbers as breeding birds. Both species were systematically persecuted by humans, with guns and by habitat loss. In the 1950s, the introduction of DDT, which bio-accumulates and caused egg-shell thinning led the species to the brink of extinction. The Bald Eagle was rescued from obliteration by the passage of the Endangered Species Act in 1973, and federal listing in 1978. DDT was banned even before this, in 1972, but it took the population years to recover. I recorded my first Bald Eagle sighting in 1977 in central Minnesota. Today, the population of Bald Eagles stands at 317,000 and is increasing.
Bald Eagle nest close to water. The birds mate for life and engage in dramatic aerial displays during courtship. The sexes work co-operatively on nest building, crafting it out of sticks and lining the interior with lichens, feathers, dried grass and other soft material which results in some very large nests, the largest bird nests in the world. One eagle nest weighed over two tons.
Both parents incubate; incubation lasts about a month. Young eaglets fledge in ten to twelve weeks. Bald eagles will not breed until four years old. They wander about in their “teen” years, straying widely from their nest site. Eagles are extremely long-lived, even in the wild. The oldest wild eagle was at least 38 years old. It was found killed by a car in 2015; it had been banded in 1977.
Bald Eagles are apex predators. Very little in the wild can harm them, although smaller birds like jays and crows might harass. The biggest threat to their existence is human activity. The number one killer of bald eagles is lead poisoning. A study conducted of 1200 eagles done 2010 – 2018 found that 47 % of Bald Eagles and 46% of Golden Eagles had chronic lead poisoning. Even a tiny amount can kill a bird within days. Because of their penchant for carrion, eagles encounter lead in gut piles left by deer hunters using lead bullets. The Raptor Center at the University of Minnesota tests all in-coming eagles and finds that 80-90% of them have some lead in their system. For more on the use of lead bullets and lead poisoning, see: https://raptor.umn.edu/about-us/our-research/lead-poisoning.
Bald Eagles are also in jeopardy when they feed on deer carcasses and other road kill near highways. The big birds tend to stand their ground when they see a car approaching, assuming it will give way to them. By the time they decide it is time to leave, it is too late.
Wind farms and transmission lines also take a toll on eagles. The USFWS issues permits allowing for a certain number of eagle deaths, called “incidental take.” The service takes into account where the turbines or lines are sited. They cannot, for example, be within 660 feet of a bald eagle nest, and in issuing the permit, also considers the relative abundance of eagles in the area. It is distressing that a species so recently considered endangered must be subjected to a “takings” assessment. However, proponents of renewable energy point out that eagles also suffer the effects of climate change.
Overall, the come-back of the Bald Eagle is considered a genuine success story. The birds’ recovery puts them in a good position to withstand a changing climate.
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