This past week was July 4th, the United States’ Independence Day. So, I thought it was an excellent time to take a closer look at the U.S.’s national bird: the bald eagle.
Bald eagles (Haliaeetus leucocephalus) are a type of sea eagle, large fish-eating eagles that live along the water. You typically find bald eagles along inland rivers and large lakes, and you’ll only see them in North America. In fact, bald eagles are the only eagle that is native only to North America. Like all sea eagles, bald eagles have high-arched beaks, bare lower legs, and rough toes for grasping slippery fish.
Why bald?
Bald eagles aren’t actually bald – their heads are indeed covered in feathers! Instead, the name ‘bald’ comes from an old English word, ‘balde,’ which means white. This, of course, refers to the snowy white feathers covering a bald eagle’s head.
Juvenile bald eagles don’t have the white head of the adults and are instead brown with a whitish tail and wing linings. It isn’t until they reach 4 to 5 years of age that the pure white head and tail grow. Put another way: it takes a few years for bald eagles to go bald!
Totally random fun fact: ‘balde’ is also where we get ‘piebald’ from! Piebald animals (like a piebald horse) have irregular black and white patches.
Big bird
Bald eagles are big, with long, broad wings that help them stay aloft by soaring on warm pillars of air.
Like many raptors, bald eagles demonstrate what is known as ‘reverse sexual dimorphism.’ We call animals where the male is larger than the female ‘sexually dimorphic.’ But in bald eagles, females tend to be larger than males. While male bald eagles can grow to be an impressive 36 in (90 cm) long with a wingspan of 6.6 ft (2 m), females may reach 43 in (108 cm) long with a massive wingspan of 8 ft (2.5 m). This size difference may be because females take the lead in gathering nesting materials.
Speaking of nests, bald eagles need big nests and make the largest nests of any bird in North America. Bald eagles nest in platforms of sticks built on top of an isolated tree or pinnacle of rock. This placement makes it easy for the birds to launch into a soaring flight to a nearby body of water. Although bald eagle nests are typically 5 ft (1.5 m) wide, older nests that have been used for years can be almost twice that size. The largest bald eagle nest was used for over 30 years and weighed 2 tons when the tree finally fell!
Sometimes hunter
Remember, bald eagles are sea eagles – their talons are shaped and textured to catch fish. And so, fish make up a large proportion of their diet. Bald eagles will swoop down to pluck fish out of the water. They’ll even sometimes follow other seabirds to find where the fish are swimming!
Fish are by no means the only food in their diet. Bald eagles eat other birds, small mammals, snakes, turtles, and crabs. But whatever they decide to eat, bald eagles have no issue hunting it. With razor-like talons that can carry up to 8 pounds and eyes that can see prey from up to a mile away, bald eagles are formidable hunters.
But sometimes, bald eagles refuse to hunt. Bald eagles are not above eating carrion that they find in a bid to conserve energy. Some days, they’ll even resort to outright theft, harassing ospreys and other raptors until the prey is dropped and the bald eagle can retrieve it. This tendency towards thieving is why Benjamin Franklin thought the bald eagle was unsuited to be the U.S. national bird.
‘Majestic’ voice
Bald eagles sound nothing like what you see in the movies. Instead of a harsh cry, bald eagles have relatively weak and high-pitched vocalizations. Movie makers weren’t impressed, so they dubbed the bald eagle with the cry of a red-tailed hawk.
In addition to their chirps, bald eagles may also use visual displays to communicate, such as head and wing motions. Breeding pairs will chirp to each other when returning to the nest and will engage in flying displays to strengthen their bond. During these displays, the pair swoop at each other before finally clasping feet mid-air. Then, in what is known as a ‘cart-wheel display,’ the birds will spin as they plummet towards the ground.
Conservation victory
Many people consider the bald eagle to be a conservation victory. While there may have been hundreds of thousands of bald eagles in North America in the 1700s, their numbers steadily declined due to hunting over the next two centuries.
Even after hunting was outlawed in the U.S. via the Bald Eagle Protection Act in 1940, the bald eagle population continued dropping. This was due to the effects of the pesticide DDT. The pesticide accumulated in their bodies as the bald eagles ate prey animals that had eaten plants coated with DDT. The problem was that DDT interfered with eggshell formation, so the eagles laid eggs with thin, weak shells. These eggs were easily broken by things like the parents sitting on or moving them; as a result, fewer young were born. By the end of the 1960s, fewer than 450 nesting pairs of bald eagles existed.
Soon, though, DDT use was banned, and the bald eagle was officially placed on the U.S. endangered species list. Thanks to stronger eggshells and government protection, the bald eagle population started to rebound. Today, there are over 71,000 nesting pairs in the U.S.
Thanks to these protections, there’s a good chance you could see a bald eagle in the wild today!
Resources
Smithsonian’s National Zoo and Conservation Biology Institute
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