Animal Spotlight: Bald Eagle

bald eagle sentinels
Photo By: David Hoffmann

Taxonomy:

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Aves
  • Order: Accipitriformes
  • Family: Accipitridae
  • Genus: Haliaeetus
  • Species: Leucocephalus
  • Females are larger than the males
  • Average Height: 2.5-3 ft (0.75-1 meters)
  • Average Wingspan: 6.5-7.5 ft (2-2.3 meters)
  • Average Lifespan In the Wild: 20-30 years
  • Longest Lifespan in Captivity: 48 years
  • Average Weight: 6-8 pounds (2.7-3.6 kg)

Bald eagles are one of the most recognizable birds in the United States; after all, it is the designated national bird. They are large, predatory raptors. As the largest raptor species found in North America, they are only second in size to the California condor.

Distinguished by a white head and white tail feathers, bald eagles are powerful creatures, similar to golden eagles. One may confuse the two species since young bald eagles remain a dark brown until they acquire their characteristic plumage at the age of four or five. One distinction between the two, even during the early years, is that only the tops of the bald eagle’s legs have feathers, whereas golden eagle’s are feathered all the way down. The hooked bills, legs,and feet are a deep yellow.

Range:

As a North American bird species, the bald eagle’s range extends from the Mexican border (Baja California and Florida) through the United States into Canada (Newfoundland and Alaska).

Bald eagles are migratory creatures and are often seen migrating to open waters in the winter months. They breed in areas such as Alaska (where their largest population lives), Canada, Pacific Northwest, along the East Coast, Mississippi River, Gulf Coast, and around the Great Lakes. For the most part, these regions will have bald eagle residents all year round but for the rest of the United States, the raptors can only be seen during the winter and their migration.

This species are almost always found near water, along large rivers, lakes, sea coast, coastal marshes, and reservoirs that contain lots of fish. During the summer, the eagles can be seen soaring above lakes in the nearby trees. In the winter, they can be seen around any unfrozen body of water. When migrating, bald eagles are seen near all types of water habitats.

Anatomy:

tumblr_mdx9ljvppd1r2q3bbo1_500
Scientific Illustration Tumblr

A bald eagle’s skeleton typically weighs about half a pound, only 5-6% of its total weight. Eagle bones, like most birds’, are hollow and light, aiding the raptor’s flight. Its feathers will weigh twice the amount.

Its hooked beak is a strong weapon used for tearing. The edge of the upper mandible is sharp enough to slice tough skin, and with the lower mandible, creates a scissors effect. The beak are made of keratin, the same substance as human’s hair and fingernails, and will grow continuously unless worn down by use. Despite its strength, the eagle’s beak is also delicate enough to groom the feathers of its mate or feed portions of food to a newly hatched chick.

Though the raptor has a strong, hooked beak to tear its food, its powerful, taloned feet are used to capture prey. Talons are important tools for hunting and defense, killing their prey by penetrating its flesh with their talons. Eagles can open and close their talons at will. If an eagle is dragged into the water by a heavy fish, it is usually because the eagle refuses to release it. To keep in perspective, a bald eagle’s lifting power is about four pounds. Like the beak, talons are also made of keratin and will also grow continuously.

A bald eagle’s plumage is one of its notable features. Each bird has about 7,000 feathers that make flight possible. Eagle feathers are lightweight, extremely strong, hollow, waterproof and highly flexible. The feather structure makes pliability, or flexibility, possible. The overlapping feathers form a dense covering, with several layers serving different functions.

The feathers will also trap layers of air. Using this adaptation, these raptors can maintain the raptor’s body temperature just by changing the position of its feathers. When an eagle wishes to warm itself on a cold morning, it will ruffle and rotate its feathers for the air pockets to either be opened to the air or drawn together to reduce the insulating effect.

The tail and its tail feathers are extremely important for flight and maneuvering. When soaring or gliding, the bald eagle will spread out its tail feathers in order to attain the largest surface area, increasing the effect of thermals and updrafts. Its tail aids the eagle is braking when landing or stabilizing during a controlled dive or swoop toward prey.

bald eagles agility
Photo By: Stuart Sanders

As a predator and raptor, bald eagles will have similar characteristic that similar species have: excellent eyesight. Though an eagle’s eye is almost as large as a human’s its sharpness is at least four times a human’s perfect vision. The eye’s frontal location allows for excellent binocular vision as well as peripheral vision.

Unlike mammals, where air only moves through the lungs once, birds will have air passes through the lungs twice with each breath cycle. A bald eagle’s respiratory system allows for air to move in through the lungs into the air sacs before moving back through the lungs and out.

Eagle sounds are commonly described as shrill, high-pitched, and twittering. Though it does not have vocal cords, sound is produced in the syrinx, a bondy chamber located where the trachea divides to the lungs. Eagle calls may be a way of reinforcing the bond between the male and female as well as to warn other raptors and predators that an area is defended.

Diet:

bald eagle catch
Photo By: Wendy Dillion

Eagles prefer fish as their staple food, often capturing them by swooping down and snatching the prey from the water’s surface. Another technique is to wade in the shallow waters to catch the fish with the bill.

When fish are not available, bald eagles will also hunt birds, particularly waterfowl such as ducks, the occasional small mammals like rabbits and muskrats, turtles, and snakes. The eagles will also willingly take carrion and are notorious for robbing osprey of their catches. They will wait on their perch for an osprey to return to its nest with a fish in its talons. Then, the bigger raptor will harass the smaller one until it is forced to drop its prey.

Behavior:

Bald eagle partners are known to bond for life. The birds who reside in the south tend to remain near their breeding territory throughout the year. More northern birds will travel together over long migrant distances during the winter months.

Initiation of courtship depends on the latitude. Southern birds will begin courtship and nesting activity in the late fall or early winter, but the northern birds will wait out winter to court and nest in early spring.

To build a nest, the eagle pair will choose their nest location to be near water in tall trees or cliffs. Once the large sticks are placed for the framework, the nest is lined with twigs, grasses, and other soft materials. Sometimes, the same nest is reused for years by a pair.

Bald eagles will lay two, maybe three, eggs that will be incubated by both parents. After 34 to 36 days, the eggs hatch but typically, only one chick survives. If food is plentiful, the adults may rear two or occasionally three chicks simultaneously. The young birds will fledge after 12 months but will remain with the parents for an additional month.

bald eagles nest
Photo By: MoJophotos Photography

Conservation/Threats:

Bald eagles, despite being the United States’ national bird, has suffered throughout the 1900s. When it was adopted as the national symbol in 1782, there were between 25,000 to 75,000 birds nesting in the lower 48 states, excluding Alaska and Hawaii. Since then, illegal shooting, habitat destruction, lead poisoning, DDT, and other chemical pollutants’ contamination has reduced numbers to only 418 pairs by 1963.

Shooting the national bird came about because while bald eagles will primarily eat fish and carrion, they were considered to have preyed on chickens, lambs, and other domestic livestock. Consequently, the large raptors were shot to eliminate a perceived threat.

However, the single-most important regulation affecting bald eagle populations was DDT. Shortly after World War II, DDT was hailed as a new pesticide to control mosquitoes and other insects. But the chemicals washed into nearby waterways and were absorbed by the aquatic plants and fish. With a diet primarily of fish, bald eagles were quickly poisoned with DDT. The chemical interfered with the ability of the raptors to produce strong eggshells. As a result, their eggs had thin shells that often broke during incubation or failed to hatch. DDT was considered safe until Rachel Carson’s Silent Spring revealed the dangers of the pesticide. With the new information, the Environmental Protection Agency banned fDDT or most uses in the United States in 1972 and became one of the biggest beginning steps for bald eagle recovery.

Legal protections began in 1940 with the Bald Eagle Protection Act. Later, protections continued with the Endangered Species Preservation Act of 1966 as well as being listed in 1978 under the Endangered Species Act of 1973. Listing the species as endangered allowed the U.S. Fish and Wildlife Service with its partners to accelerate recovery through captive breeding programs, reintroduction efforts, law enforcement, and nest site protection.

For the next 17 years the eagles were declared endangered in most of the country, the raptors experienced a strong increase in numbers and an expansion in range. Private organizations, state, and federal agencies counted 4,450 occupied nesting territories, a ten-fold increase from 1963. In 1995, U.S. Fish and Wildlife Service downlisted the species from endangered to threatened.

Despite the spectacular recovery, bald eagles are still threatened by illegal shooting and loss of habitat. Lead poisoning from shot ingested when feeding on carrion was a major issue prior to the disuse of lead shot for waterfowl hunting in 1991. Even though lead shots are no longer used, large quantities of lead remains, in addition to DDT residues, in the environment.

bald eagles feet first
Photo By: Henrik Nilsson

Based on the most recent population figures at the time, there were at least 9,789 nesting pairs throughout the contiguous United States. With that, on June 28, 2007, U.S. Fish and Wildlife Service announced that the recovery of the bald eagle has deemed the removal of the species from the list of threatened and endangered species.

Even without the protections that the Endangered Species Act provides, the species will still be protected by the Migratory Bird Treaty Act and the Bald and Golden Eagle Protection Act, an updated version to include the golden eagle. Both laws prohibit killing, selling, or harming the eagles, their nests, and their eggs.

Per the Endangered Species Act, the U.S. Fish and Wildlife Service will continue to work with state wildlife agencies to monitor the state of bald eagles for at least five years. If protections is needed once again, the federal agency will relist the bald eagle as endangered or threatened. In the meantime, individual states may pass or implement laws to protect bald eagles in their region.

Interesting Facts:

  • The bald eagle’s scientific name means “white-headed sea-eagle”.
  • Although unique to North America, its closest relatives include the African fish-eagle from the sub-Saharan Africa and the white-tailed sea eagle from Eurasia.
  • Using thermal convection currents, bald eagles can soar for hours at up to 3,000 meters (10,000 feet) in the air.
  • June 20 is National Bald Eagle Day, meant to “honor our national symbol, raise awareness for protecting the Bald Eagle, assist in the recovery of their natural environments and take part in educational outreach”.
  • Eagles do not sweat.
  • The bald eagle is a symbol for strength, courage, and freedom.
  • When cruising, bald eagles can fly about 40 mph (65 km/hr).
  • Bald eagles are not only the national bird of the United States, it is also the national animal.
  • A group of eagles soaring is described as a “kettle of eagles”.
  • Benjamin Franklin hated the idea of the bald eagle as the national symbol, claiming he is “a bird of bad moral character” and “does not get his living honestly”, pointing to the eagle’s behavior to steal from ospreys. Instead, Franklin wanted the “much more respectable” native turkey to be the national symbol.
  • Native Americans believe that a lone eagle feather conveys great power. Many of their ceremonies and legends include the eagle’s primaries and tail feathers.
  • The bald eagle is found on the back of a quarter and one dollar bill holding an olive branch and arrows.

Resourcs + For More Reading

Bald Eagle Fact Sheet

National Wildlife Federation: Bald Eagle

Natural History, Ecology, and History of Recovery of the Bald Eagle

Bald Eagle Haliaeetus leucocephalus

National Geographic: Bald Eagle

Bald Eagle Information

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