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12.9: Haliaeetus leucocephalus: Bald Eagle

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Common Name

  • Bald Eagle
  • American Bald Eagle
  • American Eagle
  • Fishing Eagle
  • White-Headed Eagle
  • White-Headed Sea Eagle

Description

Haliaeetus leucocephalus, which means “The sea eagle with a white head,” is a species of the family Accipitridae, the eagle family. Within this family is the genus Haliaeetus, or the fish eagles, which include birds like Haliaeetus pelagicus (Steller's sea eagle) or Haliaeetus albicilla (grey sea eagle/white tailed eagle). The white tailed eagle looks almost identical to the Haliaeetus leucocephalus from a distance, in part because of the head color, which is light grey. H. leucocephalus is by far the most famous of the genus Haliaeetus, mostly because it is a symbol of the United States of America. It is on the seals of the President, Air Force, Navy, Department of Defense, FBI, and most other government offices, and also US 101st Airborne division’s shoulder patch insignia. The bald eagle has a wingspan of 5.9-7.5 ft (1.8-2.3 metres), and a body length of 2.3-3.3 ft (0.7-1 metres). It has a dark brown body as well as a white head and tail. It has a yellow beak.

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Aves
  • Order: Accipitriformes
  • Family: Accipitridae
  • Genus: Haliaeetus
  • Species: H. leucocephalus

Habitat

Haliaeetus leucocephalus usually has its nests near water sources, such as lakes, marshes, rivers, or the ocean. It breeds all over North America from Alaska to Baja California, from eastern Canada to the Aleutian Islands. It usually builds its nests at the tops of tall trees.

Biology

Cell Biology

Haliaeetus leucocephalus has, like all animals, eukaryotic cells, which are cells that has a nucleus several organelles. Organelles include the nucleus, which contains the DNA (genetic material), and the mitochondria, the powerhouse of the cell. The vesicles are the transportation organelles, vacuoles, the storage centers, and ribosomes are the protein factories. The endoplasmic reticulum is a membrane which helps transport the proteins. The Golgi apparatus is kind of like the post office of the cell, in that it “puts the delivery address” on the cell and helps transport it. Finally the cell membrane is the outer protection membrane.

Specialized cells in bald eagles include cones. Cones are cells in your eyes, which help with sharp vision, colors, details, and night vision. Humans (Homo sapiens) also have cones, but bald eagles have thousands more in their eyes, which gives them their incredible eyesight, which is about 4 times better than a humans eyesight, and can spot a small fish from a mile away. An average Homo sapiens has 20/20 eyesight. An average Haliaeetus leucocephalus has at least 20/5 eyesight, if not better.

Evolution

The first official Haliaeetus leucocephalus ever was found in 1766, although fossil evidence of what could possibly be bald eagles appears to be one million years old. They seem to have evolved from a species of bird called a kite. Like Haliaeetus leucocephalus, this ancestor hunted fish and scavenged them. Many other details, such as featherless feet, are in common between the two animals. Birds in general all evolved from Theropod dinosaurs, such as Tyrannosaurus and Velociraptor, which are very well known because of the very famous movie Jurassic Park (1993). Most bodily structures in birds seem to be similar to the theropod Deinonychus. The first flying dinosaur was Archeopteryx, which developed arms that allowed it to glide, and eventually fly

Ecology

Haliaeetus leucocephalus is a predator, preying mostly on fish, but will not pass up the opportunity to catch rodents it sees on the ground, and it will also steal food from other animals. Unlike most other bird species, the bald eagle’s nests are actually reusable, so it does not have to build a new one every time it will reproduce. It also builds the largest nest of any North American bird, up to 13 feet deep and 8.5 feet wide. For the majority of the twentieth century, the bald eagle was an endangered species as a result as a pesticide called DDT. DDT actually affects an adult bird’s calcium metabolism, causing it to lay a bad egg with a thin, brittle shell, making it nearly impossible to hatch. At its lowest point, there were only 412 nesting pairs in the United States in the 1950s. There were also illegal shootings, some for mistaken beliefs, or others because it was mistaken for other species, such as one that was shot because it was mistaken for a white tailed eagle. Juveniles are often mistaken for the Aquila chrysaetos (Golden Eagle), however this should not result in death as both are protected by US Law.

Anatomy and Physiology

Like all other birds, the bald eagle has a four-chambered heart. It also has a two-cycle respiration system, as well as a one-way flow for respiration. Both of the breathing cycles occur at the same time. The bald eagle never reaches speeds that would interfere with their breathing. The bald eagle has about 7,000 feathers. Its eyes are almost as big as a human’s, and it can see at least four times sharper. Its eyes have two eyelids, which protect their very powerful eyes. The outer eyelid is thick and provides great protection when both eyelids are closed. The inner eyelid is very thin, but still provides good protection. Interestingly, it can see through its inner eyelid, so it can have both eyes closed but still see! It is diurnal, and is not renowned for its hearing which, unlike its eyesight, is about as good as a humans. Its wings are not designed for low flying, as the bald eagle is normally a high-flying eagle. The bald eagle reaches sexual maturity at age four to five. A bald eagle lays 1-3 eggs a time. The eggs are then incubated by both parents for 34-36 days before they hatch. For about 5 weeks after it has hatched, a baby bald eagle cannot walk. When it first takes to the skies, interestingly, is a dark black all over! Even more interesting, it is a little larger than its parents. In over the next few years, its plumage changes, the top looks like it is from a bird in the process of shedding feathers, the bottom appears to have white wings and black feathers coming out from them. This can be very confusing to birdwatchers. It is believed by many that Washington’s eagle, “discovered” by John James Audubon, was an immature bald eagle. Interestingly, Audubon knew what an immature bald eagle looked like, and he had made paintings of them. Haliaeetus leucocephalus lives for about 20-25 years in the wild, but has been known to live longer in captivity, as one was recorded to have lived about twice as long as the life expectancy in the wild.

Behavior

The Haliaeetus leucocephalus is can be an aggressive species, and it mates for life. The bald eagle is known to steal food from other animals. Because of this, scientist, American founding father and revolutionary, Benjamin Franklin, was appalled, and said precisely in a letter “he is a bird of bad moral character”. Instead, he suggested that Meleagris gallopavo (the wild turkey) become the national bird. Haliaeetus leucocephalus lacks a gizzard, so it must catch and kill everything it eats.

References

Attribution

Authors

  • Maxwell Phillip Hoffman

Supervising Faculty

  • Amy Huff Shah

Affiliation

  • Museum School, San Diego, California

Image Attributions

Description

Categories:

Grades:

6 , 7 , 8 , 9 , 10 , 11 , 12

Date Created:

Jul 18, 2013

Last Modified:

Aug 19, 2014
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