August 2017 - The Bald Eagle
 Photo courtesy of Frank R. Perez
It has been one decade since the Bald Eagle was removed from the Endangered Species list. Historic levels of eagles reached 100,000 before plummeting to only 417 pairs in 1963. Banning DDT allowed their numbers to increase by 50% in the last ten years to about 15,000 in the lower 48 states. Eagles soar in all states except Hawaii with Alaska having the largest number of eagles.
Their range is most of Canada and Alaska, all of the contiguous United States and northern Mexico. They are found in every state in the continental United States and every province in Canada. You will find them near bodies of water with abundant food and old growth trees for nesting. They spend their breeding season near any kind of wetland habitat; seacoasts, rivers, lakes, marshes and open bodies of water. Bald eagles are very powerful fliers, gliding and flapping over large distances and up to an altitude of 10,000 feet. To save energy, they use thermals, flying high to catch one and gliding down to pick up the next one. Several eagles gliding together are called a “kettle of eagles.” Even immature bald eagles (under four years old) will travel hundreds of miles per day! Our birds in California may reach Alaska. This bird fishes for much of its food catching fish right out of the water with its strong talons. The talons have spicules (needle-like spikes) which allow them to grasp fish. Though fish (salmon and trout) make up the majority of their diet, they also eat water birds, mammals (rabbits, hares, squirrels and raccoons) and other small prey. Bald eagles will harass osprey until they drop their prey, and then swoop in to catch the prey in midair. They will also follow bears, wolves and foxes to scavenge their kills. Bald eagles can fly with fish that equal and sometimes exceed their body weight. The record for the heaviest load carried by a flying bird is a bald eagle flying with a 15-pound mule deer fawn. Bald eagles build the largest nests of any North American bird. The largest nest was found in St. Petersburg, Florida and was 2.9 meters across, 6.1 meters tall. For heaviest nest, we go to Vermillion, Ohio, for a nest that weighed almost two metric tons and was in use for 34 years until the tree blew down. They nest in old-growth coniferous or hardwood trees which provide good perching, roosting and nesting. They like large trees that provide good visibility near bodies of water and near sources of prey but away from human activity. Their nests are high in the trees, from 52 to 125 feet up. Though the female is responsible for placing the nesting materials, both sexes bring the sticks and other building material to the nest. They will weave sticks together and fill in with grass, moss or cornstalks. The inside has two layers; first, a layer of lichen or fine sticks, then a softer layer of downy feathers and greenery completes the nest. Building a nest is hard work taking up to three months, and like the nest in Ohio, may be used year after year. Bald eagles have one brood of 1 to 3 eggs. They take 34-36 days to incubate and will fledge in 56 to 98 days. Both parents feed the young, tearing food into bite size pieces and feeding to their hungry family. At 3-6 weeks, young begin to explore food dropped in the nest. Though we call them “bald” eagles, they really are not bald. Their white head contrasting against a very dark body gives the impression of baldness. Males and females have the same plumage, but the females are about 25% larger than the males. A bald eagle has a white head and white tail with uniformly dark feathers on its body. They have bright yellow irises, yellow feet and a yellow, hooked beak. With a body length of 28-40 inches, a wingspan of almost 6 to 7.5 feet and weighing in at 6.6 to 13.9 pounds, this is no little songbird. The only other, larger raptor-like bird is the California Condor. They are strong flyers soaring on thermal currents flapping and gliding at 35-43 miles per hour. Bald eagles increase in size as their range moves further from the equator. This is Bergmann’s ecogeographical rule that larger sized representatives of a species will be found in colder environments and smaller sizes closer to the equator where it is warmer. Their 7,000 feathers provide insulation from cold and protect them from the heat of the sun. Northern birds are migratory if water sources are frozen making their fish prey unavailable, southern birds stay in their breeding territory all year. Northern birds migrate to coasts or south where prey is plentiful. Bald eagles are the national bird and national animal and appear on the Great Seal of the United States. The oldest recorded Bald Eagle was at least 38 years old. He had been banded in New York in 1977, and was killed by a car in 2015. |
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