The American Bald Eagle
The American Bald EagleHeliaeetius Leucocephalus, also known as the American Bald Eagle is a bird no one is unaware of. This bird is the only species of eagles found in North America and it is found only in this region. The word Bald initially meant hence the name Bald Eagle since its head is white. This bird is found in most of Alaska, Canada and Mexico. About 70% of this bird’s total population is found is Alaska. Nowadays, only about 70,000 Bald eagles are present of these, more than half i.e. are in Alaska whereas the rest are usually found in British Columbia, Mexico and Canada (Stout, 1997).
The life cycle of American Bald eagle starts when an egg hatches after an incubation period of around 35 days and new baby bird is born. The baby bird grows rapidly i.e. gains a weight of one pound/4weeks and reaches its age of sexual maturity at around four to five years. At that age, the birds are eager to find a partner and once a partner is found, they stay together for life (Morrison, 1998). The mating season of this eagle is usually from September to January and eggs are laid usually in March. After the eggs are laid, both the male and female share equal duties to guard the eggs until they hatch (Datrich, 1983).
The most outstanding feature of a Bald Eagle that helps locate and catch its prey are it eyes. Eyes of a Bald Eagle are fascinating in the way that they contain two fovea i.e. centers of focus. These centers of focus are usually single in normal eyes but being two in this eagle enables it too see both straight and sideways at the same time. Another most striking feature of the eyes of this Bald Eagle are their Nictitating membranes. These transparent membranes move from front backwards wiping off the dirt. Being transparent, these membranes do not obstruct vision and enable the eagle’s eyes to get rid of dirt too. Also, the eyes of a bald eagle have four times greater sharpness than a 6/6 human eyes which enable it spot a prey in an area of three to four square mile while at a height of one thousand feet.
This eagle’s evolutionary study takes back to the age of dinosaurs. The eagle’s ancestors are supposed to be reptiles millions of years ago which evolved into Ancient Birds known as Kites. Today’s American Bald Eagle is supposed to be a successor of these Kites with its feathers derived from scales of these reptiles. Millions of years ago, reptiles evolved into birds, evidence of this is found in the fossils of a dinosaur Archeopterx which died about 65 million years ago. This dino had wings and clawed foot bearing resemblance to the evolved birds (Weidensaul, 1996).
In 2005, a study was conducted to observe the phylogenetic relationship between different species of eagles. The birds were of Acciptridae family and their mitochondrial DNA samples were taken. Old world vulture (two families) and four subfamilies of eagles were studied and it was found that Sea eagles and booted are monophyletic whereas no monophyly was found between the rest of the species. Also, gymnogenes and crane hawks were not found to be of any relation. The main purpose of this study was to find out an evolutionary relationship between these subfamilies of birds of prey as compared to the morphologic similarities and dissimilarities (Lerner, 2005).
American Bald Eagle Information. (n.d.). Retrieved December 17, 2014, from http://www.baldeagleinfo.com
Detrich, Philip J. 1983. “Status of the Bald Eagle in California.” Pg.80-83. In Nancy Venizebs and Celeste Grijalva,eds. RAPTORS. San Francisco Zoological Society.
Lerner, H. R. L., & Mindell, D. P. (November 01, 2005). Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA. Molecular Phylogenetics and Evolution, 37, 2, 327-346.
Morrison, G. (1998). Bald eagle. Boston: Houghton Mifflin Co.
Stout, J. H., Trust, K. A., & U.S. Fish and Wildlife Service. (1997). Contaminant residues in bald eagles (Heliaeetus leucocephalus) from Adak Island, Alaska. Anchorage, Alaska: Ecological Services Anchorage Field Office.
Weidensaul, Scott. 1996. RAPTORS: THE BIRDS OF PREY.Lyons and Burford Publishers.