The Bald Eagle

img_5846With the political election and campaigns recently coming to the end, many American citizens find themselves questioning where this country is going and what the country stands for now. Along with symbols like the American flag and the Liberty Bell, the Bald Eagle remains a symbol of the United States freedom along with it’s amazing biology, unique diet, and profound history.

With all of the political controversy with today’s American society, the Bald Eagle, also known as Haliaeetus leucocephalus scientifically, remains a sign of freedom and liberty along with its amazing biology.  As seen from the pictures above, a Bald Eagle can turn its head a full 180 degrees in each direction. This is due to the 14 cervical vertebrae located near the head that give the Bald Eagle a greater degree of rotation as compared to the human neck that can rotate 90 degrees both ways because the human neck only has seven vertebrae in the neck. This complete rotation of the neck in the bald eagle allows the bald eagle to search for prey at a much greater length.

Along with the great degree of rotation, the advanced eye of the Bald Eagle also allows the bird a greater chance for capture of prey. The bird’s eye consists of 2 foveae; a foveae is a slight depression in the retina of the eye that allows for extreme sharpness in vision. Since the bird has 2 foveae, it can have multiple points of focus. For example, it can focus on one prey in front of it and another from the side at the same time. With this advanced eye comes a nictitating membrane. The nictitating membrane is a translucent membrane on the inside of the eyelids of the Bald Eagle that allows it wipe away dirt from front to back of the cornea. An interesting factor of the nictitating membrane is that since the membrane is translucent, the bird can still see the entire time that the membrane is cleaning the eye. This allows for further sharp focus by the bird when it is looking for prey. For example, if there is dirt in the eye, and the eagle sees prey available for capture, it can still focus on the prey even though dirt may be blocking the eye.

Besides such advanced features in the eye, the Bald Eagle would be nothing without its feathers. The feathers not only allow for flight but also for insulation of heat and avoidance of moisture. The first layer of feathers is the down, which is the closest to the skin of the bird and also allows for insulation of heat. The next layer is the contour and primary feathers. These feathers not only give the shape of the wings, they also give the bird its protection from moisture and aerodynamic ability for flight. Both the down and the contour/primary feathers result in the Bald Eagle to have a wingspan between six and eight feet, which  are needed to protect and preserve the bird at the top of its food chain.

With the superior head, eye, and feathers, this bird of prey also has a very developed beak and talons to further aid in the capture of prey. Both the beak and talons are made of keratin just like in the nails of humans. The talons consist of three toes facing forward and a fourth toe, the hallux, facing backwards that lets the eagle use the muscles in its legs to get a vise-like grip on the prey. Once the bird crushes the prey with its talons, it then uses its beak to pick apart the prey for eating.

Once the Bald Eagle devours its prey, there are times when the bird must go days without ever finding food. Although the bird can eat up to a third of its own body weight (about 6.5 to 14 lbs.), the stomach is actually only about the size of the walnut, which can explain why the bird can handle not having food for quite a while. What also aids in the lack of food availability for the Bald Eagle is the crop in the esophagus. The crop is stores excess food when the stomach is full for later digestion by the bird; when the small stomach is full, the rest of the food is stored in the crop until the food in the stomach has been digested completely. This explains why the Bald Eagle can go for such a long time without having food.

Despite having all these sophisticated tools for capture of prey in the bird’s anatomy, the Bald Eagle’s diet is just as important as the biology of how the bird attains food. Because the bird is from the genus Haliaeetus, which translates to “sea eagle” from Latin, it is clear that the bird is usually located along the coasts of North America but also near the rivers and Great Lakes. Since the bird’s habitat is near water, the Bald Eagle mostly feeds on fish but will eat ducks and other birds as well if available. A distinctive technique that Bald Eagles use is temperature with regards to catching prey. If the weather is too cold, the bird will try to avoid fish in water as prey. This is due to the fact that if the bird’s talons make contact with the water, it can get hypothermia, which can take a while to where off especially if the overall environment is cold.

As it has been shown, the Bald Eagle has many of aspects in its anatomy and diet that make it such a magnificent species, which is why it’s easy to understand why this animal was chosen as the national bird of the United States in 1782. Unfortunately, the Bald Eagle was recognized as a threat to farm life. As stated before, the Bald Eagle feeds usually on fish, but will eat whatever birds are easy to obtain, which will include farm-raised chickens. This became harmful for farmers and their livestock, so people began hunting the eagles for sport, which resulted in a decline in the Bald Eagle population. It was not until 1940, over 100 years after they were realized as a threat, that Congress passed the Bald Eagle Protection Act to protect the Bald Eagle from being hunted since it is the symbol of the United States. This act eventually became known as the Bald and Golden Eagle Act of 1962 to extend the act to protect the Golden Eagle as well. This act initially helped the population of Bald Eagle’s increase until the end of World War II. After World War II, DDT was brought in to control mosquitoes and other insects around plants. Residues of the DDT got into the water systems and, eventually, into the bloodstream of fishes. Since the Bald Eagle mostly eat fish, the DDT had a domino effect caused eggs not to hatch because the DDT made the eggs of the Bald Eagle’s so thin that it was unhealthy. Fortunately for the Bald Eagles, DDT was banned in 196 by the Environmental Protection Agency (EPA). This led to the subsequent massive population of the Bald Eagles that we have today. There are at least 9,789 nesting pairs in the United States today.

In conclusion, the Bald Eagle is such a fascinating animal from its biology and diet to its history as the national bird of the United States. This is one symbol of America we can all be sure will always remain a magnificent sight and an even more magnificent species. For more information on the Bald Eagle, visited the websites listed below. You will also find some videos with regards to the feathers and the capture/kill behavior of the Bald Eagle. The photograph at the beginning of this post was taken at the Brookfield Zoo.

Work Cited


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