Formidable Fowl FeaturesThe Bald Eagle appears on most official seals of the US government, including the presidential seal and flag. It is also seen in the logos of many federal agencies, as well as on currency and stamps. Images of the bird are etched into the stone of public buildings and displayed on screen with superheroes. Similarly, Native American cultures revered the Bald Eagle and included its feathers in many customs. You might have noticed its white plumage in passing, but take a moment to fully absorb this raptor’s striking anatomy. Bald Eagles are birds of prey. Their Latinized Ancient Greek name (Haliaeetus leucocephalus) means “sea eagle with a white head”. The adult birds are mostly brown. Their yellow legs are feather-free with large, powerful talons and they have similarly large yellow bills, which are hooked. The only white areas on the birds are the head and tail plumage. Immature Bald Eagles have mostly dark heads and tails; their brown wings and bodies are mottled with white in varying amounts. Although Bald Eagles molt throughout their lives, the molting of the youthful birds is more colorfully dramatic as they transition into adults. The process takes about five years. Their eyes lighten as they mature, as well. Bald eagles are usually between 2.5-3.5 feet inches long, with a wingspan between six and eight feet. They weigh between seven and fourteen pounds. Females are about 25% larger than males. The size of the birds varies by location. Generally, birds in colder climates are larger. They Live Near and FarBald Eagles naturally range throughout North America. They are adaptable to temperature extremes and live in varying wetland habitats, usually within two miles of seacoasts, rivers, lakes, marshes, or other large bodies of open water with an abundance of fish and old-growth trees for nesting. With available water and food resources, Bald Eagles will occupy a territory year-round. However, some populations migrate south or to the coasts in the winter in search of food. If non-breeding, or during winter, Bald Eagles may be less habitat and disturbance sensitive. They may spend time in terrestrial habitats, far away from waterways. If unfrozen water is not accessible, Bald Eagles may settle in open habitats with concentrations of medium-sized mammals, such as prairies, meadows or tundra, or open forests with regular carrion access. No Need to be The Early Bird – Not Interested in WormsBald Eagles are opportunistic carnivores and will consume a variety of prey. Fish often comprise most of their diet, though they will also eat water birds, small mammals, reptiles, and carrion. More than 400 species are known to be included in the Bald Eagle's prey spectrum. To hunt fish, Bald Eagles swoop down and snatch fish out of the water with their talons. They hold the fish in one claw and tear its flesh with the other. They may attack bird prey mid-flight. When gripping large prey such as mature salmon or geese, Bald Eagles may strenuously drag the prey in a low flight over the water to a bank, where they then dismember and consume it. When food is abundant, a Bald Eagle can gorge itself by storing over two pounds of food in a pouch in its throat called a crop. Gorging allows the bird to fast for several days if food becomes unavailable. Depending on what they have eaten, pellets are formed after a meal and are usually cast out the next morning. Bald Eagles have very strong stomach acids, and can digest bone, which aids in their own bone and egg-shell formation. Bald Eagles also feed on found carcasses and via a practice known as kleptoparasitism, by which they steal prey away from other predators. The birds are not selective about the condition or origin of the carrion they consume. It may be provided by humans, other animals, auto accidents, or natural causes. Eagle Edifice / Bird BuildingBald Eagles reuse their nests for multiple breeding seasons. The birds construct them with large sticks and line the inside with moss, grass, plant stalks, lichens, seaweed, or sod. Each season the eagles contribute more material so that the nests grow ever-larger. The birds build the largest nests of any animal species, approximately thirteen feet deep, eight feet wide, and weighing one ton! Nests ten feet wide have been recorded. Such a large structure near a water feature is prime real estate! You would think Bald Eagles would stay and enjoy the view. But they do not actively use their nests year-round. The only time they are in them is when they are raising young. Even then, the adults perch on branches to sleep. They monitor their young from the same, or nearby trees. While nesting, the birds are sensitive to human activity. They generally prefer areas with minimal human disturbance. However, sometimes individual Bald Eagle pairs will nest in areas surrounded by human activity. This variability in sensitivity to humans may be related to visibility, noise level, the extent of the area affected by humans, the eagle pair’s prior experiences with humans, and the tolerance of the individual nesting pair. Some pairs, for example, nest successfully near human activity, while others abandon nest sites in response to activities much farther away. A pair of eagles will generally return to the same nest year after year. But, many Bald Eagle pairs will also have an alternate nest within their breeding territory. The alternate nest serves as insurance in case the primary nest is destroyed early in the nesting season. If the breeding pair are in an area where there are no trees, they will nest on the ground. This has been recorded in areas largely isolated from terrestrial predators, such as Amchitka Island in Alaska. Bald Eagles will also nest on cacti and rock shelves, depending upon the habitat. Spring Chicken to Old Bird: The Bald Eagle Life CycleWhen Bald Eagles are old enough to breed (at four or five years of age) they often return to the area where they were born. Courtship involves elaborate calls and flight displays by males. Flights include swoops, chases, and cartwheels, in which they fly high, lock talons, and free-fall, separating just before hitting the ground. Pair-bonding behaviors include flying side by side, sitting shoulder to shoulder, and mutual preening. Bald Eagles make life-long commitments. Since they can live twenty to thirty years in the wild, theirs is a long partnership. If one member of a pair dies, however, the survivor will choose a new mate. Also, a pair which has repeatedly failed in breeding attempts may split and look for new mates. In New York, the breeding season for Bald Eagles is January through August. The birds typically build or reinforce their nests by mid-February and lay eggs by the end of that month. The incubation period is thirty-five days, with the eggs hatching one to several days apart, depending on when they were laid. The young remain in the nest for another ten to twelve weeks until they fly. Fledglings may continue to rely on their parents for food and other care for few weeks post fledging. In most cases, parents continue to deliver fish and other prey to the young birds until they learn to forage on their own, which occurs between four and ten weeks after leaving the nest. Juvenile Bald Eagles begin dispersing away from their parents about eight weeks after they fledge. For the next several years, the immature eagles wander widely in search of food. Once they attain adult plumage they are ready to reproduce. Bald Eagles: Neither Rare Birds nor Paltry Poultry The early 18th century US Bald Eagle population is estimated to have numbered between 300,000–500,000. But by the 1950s there were only 412 nesting pairs. The severe population drop was caused by a variety of factors. Among those was the thinning of their egg shells as a result of the biomagnification from the pesticide DDT. The chemical interfered with the birds’ calcium metabolism. This resulted in eggs that could not withstand the weight of a brooding adult. Other factors in Bald Eagle population declines were a widespread loss of suitable habitat, hunting, lead poisoning from scavenging hunted remains, motor vehicle collisions, and power-line electrocution. As people became more cognizant of the plight of Bald Eagles, various safeguards were put into effect. The birds were first protected by the 1918 Migratory Bird Treaty. The US Congress approved the Bald and Golden Eagle Protection Act in 1940, which prohibited the commercial trapping and killing of the birds. In 1967 Bald Eagles were declared an endangered species and amendments to the 1940 act further restricted commercial uses and increased penalties for violators. In 1972 DDT was banned from usage in the United States and later in Canada. With regulations in place and DDT banned, the eagle population rebounded. The Bald Eagle can now be found in growing concentrations throughout the United States and Canada, particularly near large bodies of water. The birds have been removed from the lists of endangered and threatened species. In Alaska and the state of Washington, the increase in Bald Eagles has led to decreases in other bird populations, as well has impacted the fishing industry to the point that they may be considered a pest. Apex PredatorHealthy adult Bald Eagles are not preyed upon in the wild and are thus considered apex predators. Most non-human-related mortality of the birds involves nestlings or eggs. These deaths may be due to nest collapses, starvation, sibling aggression, or inclement weather. Another significant cause of egg and nestling mortality is predation. Nest predators include wolverines, bobcats, bears, and raccoons, as well as other birds like hawks, owls, and gulls. The Bald Eagle You KnowSince immature Bald Eagles may not yet have the characteristic white plumage on their heads or tails, it is helpful to know the size, shape, and flying posture of America’s symbol to correctly identify it. As a Bald Eagle flies toward you, its wings are held straight out, unlike the more common Turkey Vulture, which soars with its wings in a V-shape. Like Bald Eagles, the wingspan of Turkey Vultures is about six feet across, though the Vultures’ body is a little shorter (about two feet long). And Turkey Vultures are actually bald! The skin on their heads turns from black to red after about a year. Bald Eagles fan their tails open as they fly; Turkey Vultures fly with a straight tail. The bodies of immature Bald Eagles are mottled brown and white; The underside of the wings of Turkey Vultures are paler, giving a two-toned appearance. The Greater Black-backed Gull is another species that is mistaken for Bald Eagles because of its dark wings. The gulls inhabit waterways along the east coast of North America, including the Hudson River. Greater Black-backed Gulls have white heads and tails, but unlike Bald Eagles, their breasts are also white. (Immature gulls have checkered white and brown breasts.) Another point of difference is that Greater Black-backed Gulls have only a five-foot wingspan and body length about two and half feet. They are smaller birds than Bald Eagles. Surprisingly, Bald Eagles make a series of chirping whistles and other high-pitched notes and calls. Hearing those sounds belie the formidable appearance of this avian, once it is seen. This is the reason the sounds attributed to Bald Eagles in films are actually those of Red Tailed Hawks, whose call is a raspy scream. FlyingBald Eagles are powerful fliers that can reach speeds of 35–43 mph. But they are not the fastest birds. Peregrine Falcons, for example, can move twice as fast. Still, Bald Eagles are considered surprisingly maneuverable in the air. They have been recorded catching up to and then swooping under geese in flight, turning over and thrusting their talons into the other bird's breast. The Hudson Valley is the Catbird Seat for Bald Eagle SightingsSince Bald Eagles often live within two and a half miles of water bodies, the Hudson River Valley gives them perfect hunting grounds for their main food sources. From Tivoli in the north, to Poughkeepsie, and Beacon in the south---and anywhere in between—keep your eyes peeled skyward looking for these massive birds. If the river is visible, you may see Bald Eagles on ice floes during winter or having a meal on an island. The birds most actively feed from 7 am - 9 am and 4 pm - 5 pm, though this may vary according to temperature and other factors such as how recently they last ate. Be prepared to wait a while. Eagle viewing requires patience. Since winter is the best time to view Bald Eagles, dress warmly and bring along a hot beverage. If you are able to stay in the warmth of your car, that is desirable. December through February allows an unfettered view of eagles in trees, sans foliage. But the freezing temperatures of winter are not for the faint of heart. Be selective when choosing the best Bald Eagle viewing days. There are several places within Dutchess County that Bald Eagles have been known to roost and may provide some sightings of these fine feathered fish-eaters. Kayaking on the Hudson will get you great access, but if you prefer to remain on terra firma there are several attractions that provide free access with clear views of the Hudson River and, thus, afford opportunities for Bald Eagle viewing. They are: Tivoli Bays Natural Heritage Area and Poet’s Walk, both in Red Hook; Wilderstein Historic Site, Rhinebeck; Vanderbilt Mansion Historic Site and FDR Historic Site, both in Hyde Park; The Walkway Over the Hudson, Poughkeepsie Rural Cemetery, and Locust Grove all in Poughkeepsie; Bowdoin Park, Wappingers Falls; and Madam Brett Park in Beacon, at the mouth of Fishkill Creek Bald Eagles may become distressed during nesting, so be mindful of this and observe them from a distance with binoculars or a long camera lens. Refrain from loud noises: honking horns, door slamming, radios playing, yelling, etc. Keep pets at home. Don't do anything to try to make the bird fly. It is important that they conserve their energy. Harassing or disturbing a Bald Eagle is a federal offense and carries heavy penalties. BALD EAGLES are iconic symbols Check out this activity to teach students about a topic that transcends science, history, art, government, and numerous other subjects.
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AuthorGertrude Katz has spent over 30 years teaching K-12 public school students all major subjects. She has taught biology and education at the college level. The majority of her career has been spent instructing biology at the secondary level. Categories
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