The bald eagle (Haliaeetus leucocephalus) is only found in North America. Its range stretches from northern Mexico to Canada and Alaska and covers all the continental United States. Due to a variety of factors, including the use of the pesticide DDT, bald eagles nearly became extinct in the contiguous United States by the 1950s. The 1940 Bald Eagle Protection Act prohibited commercial trapping and killing of bald and golden eagles, and more significantly, DDT was banned in 1972 when it was proven the pesticide interfered with the eagle’s calcium metabolism, causing either sterility or unhealthy eggs with brittle shells. In 1973, Congress passed the Endangered Species Act, and the bald eagle was listed as an endangered species. In 1995, when eagle populations in the continental U.S. began to rebound, the bald eagle was removed from the endangered species list and transferred to the threatened species list. On June 28, 2007, bald eagles were removed from the List of Endangered and Threatened Wildlife.
While Alaska’s eagles were never threatened by the use of DDT, Alaska has its own nefarious history with bald eagles. In 1917, commercial salmon fishermen convinced the Alaska Territorial Legislature that eagles killed large numbers of salmon and were competing with the fishermen’s livelihoods. This claim was later shown to be false, but the legislature enacted a bounty system on eagles that paid two dollars to anyone who turned in a pair of eagle legs. This bounty system lasted for thirty-six years and led to the killing of a confirmed 120,195 eagles, plus countless others that were never turned in for a bounty. The bounty system ended in 1953, and when Alaska became a state in 1959, its bald eagles were officially protected under the Federal Bald Eagle Protection Act of 1940. Alaska’s eagle population is now considered healthy, and one-half of the world’s 70,000 bald eagles live in Alaska. Twenty-five-hundred bald eagles reside on the Kodiak National Wildlife Refuge.
The genus Haliaeetus, the sea eagles (in Latin, hali means salt and aeetus means eagle), includes eight of the sixty species of eagles. The sea eagles live along sea coasts, lakes, and river shores. The species Haliaeetus leucocephalus (leuco means white and cephalus means head) consists of two subspecies. The southern bald eagle, Haliaeetus leucocephalus leucocephalus, is found from Baja California and Texas to South Carolina and Florida, south of 40 degrees north latitude. The northern bald eagle, Haliaeetus leucocephalus alascanus occurs north of 40 degrees north latitude. Northern bald eagles are larger than their southern cousins
Eagles are well-insulated by their feathers and are good at regulating their body temperature. Unlike many birds, they do not need to migrate to warmer areas each winter, but in many parts of the country they do migrate, sometimes long distances, in response to varying food supplies. Due to its abundant year-round food supply, Kodiak has a non-migratory eagle population. Furthermore, hundreds of eagles from the Alaskan mainland migrate to Kodiak for the winter months. Effluent from canneries and fish processing plants in the town of Kodiak provides a consistent source of food for these birds in the winter months, and hundreds of eagles can be seen in town perched in trees, on cannery rooftops, on the edges of dumpsters, and even on pickup trucks. In Uyak Bay and other remote bays on Kodiak, eagles stay near their nests all winter, feeding on fish and winter-killed deer among other things.
Since the ban on DDT and related pesticides in 1972, bald eagle populations around the country have rebounded to some degree. The bald eagle population in Alaska is healthy and stable and has never been listed as endangered or threatened by the Federal Government. Eagles in Alaska never suffered the scourge of DDT poisoning, and even now in most areas, they live in a relatively contaminant-free environment.
The Bald Eagle Protection Act imposes a fine of $10,000 and two years imprisonment for anyone who harms a bald or golden eagle. It is illegal to even have an eagle feather in your possession without a proper permit. Nevertheless, humans are still responsible for many bald eagle deaths. On Kodiak, Refuge biologists have recovered eagles that have starved to death, been killed by airplanes and cars, caught in traps, and oiled by fish slime or fossil fuels. The Exxon Valdez oil spill killed hundreds of eagles in Alaska. In January 2008, fifty eagles swooped down on a dump truck filled with fish guts outside a Kodiak seafood processing plant. Twenty of the eagles were drowned or crushed, and the rest were so slimed they had to be cleaned. Bait left unattended on a fishing boat can cause a frenzy when eagles land and start fighting over their find. If their feathers become oiled by fish slime, they become less-waterproof, and then if the eagle falls into the water, it is more susceptible to hypothermia.
In 2009, the Kodiak Electric Association (KEA) erected three wind turbines on Pillar Mountain near the town of Kodiak and added an additional three turbines in 2012. Many people worried the turbines would be a danger to eagles since turbines elsewhere in the U.S. kill an estimated 573,000 birds a year. KEA funded a study to address the concerns, and researchers determined that eagles went out of their way to avoid crossing the ridge among the turbines. No eagles were killed during the study, and according to avian biologist, Robin Corcoran, she has never received a report of a dead eagle near the turbines.
Eagles do die from electrocution on Kodiak. Many of the power poles near town are fitted with devices designed to protect eagles, but in January 2011, an eagle was electrocuted when she landed on the lowest of three cross bars on a power pole. That particular crossbar did not have a protective device because utility authorities believed there was not enough room for an eagle to land on it. The dead eagle had been banded years earlier by the Alaska Department of Fish and Game, so biologists knew she was 25 years old, the second-oldest bald eagle documented in Alaska, and one of the oldest-documented eagles in the country.
While these manmade disasters are tragic, they are uncommon and do not appear to be a threat to Alaska’s bald eagle population. A greater and less-obvious threat is the destruction of eagle-nesting habitat by logging and commercial and residential development. Eagles tend to nest in large, old trees that are not easily or quickly replaced once they are removed.
Once an eagle attains its adult plumage, it is impossible to determine its age unless it has been leg-banded by biologists. For this reason, we have limited data on the life span of bald eagles. Biologists believe 50-70% of all juvenile bald eagles die in their first year, and as many as 90% die before they are fully mature. Eagles in captivity may live 40 to 50 years. The oldest documented eagle resided in Stephentown, New York and lived to be 48-years old. On average, eagles live 15 to 20 years in the wild, and the oldest documented wild eagle was a 32-year-old bird from Maine. Alaska’s oldest eagle was a 28-year-old from the Chilkat Valley.
Eagles are fascinating birds and have been studied a great deal. Later this winter, I will dedicate more posts to eagle biology. Please leave a comment if you have a question or anything you would like to share about eagles.
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