http://www.ck12.org Chapter 12. Understanding Biodiversity: Animals: Birds
Biology
Cell Biology
Haliaeetus leucocephalushas, 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 averageHaliaeetus leucocephalus
has at least 20/5 eyesight, if not better.
Evolution
The first officialHaliaeetus leucocephalusever 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. LikeHaliaeetus 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 movieJurassic 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 leucocephalusis 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 theAquila 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