Summit Outside: The national symbol
September 29, 2012
One day an eagle was sitting on the top of a tree on Dillon Reservoir. We watched a pair of ospreys swooping down, repeatedly dive bombing it. Eventually it gave way and flew off. Recently we saw an eagle flying being chased by several gulls. A friend said he has even seen them harassed by hummingbirds. What’s with this?
When you look at the eagle it seems like such a large magnificent bird: our nation’s symbol should be at the top of the pecking order, not being pecked at.
When I started checking in the literature, I found a comment by Benjamin Franklin who said if he prevailed, the U.S. emblem might have been the wild turkey. In 1784, Franklin disparaged the national bird’s thieving tendencies and its vulnerability to harassment by small birds. “For my own part,” he wrote, “I wish the bald eagle had not been chosen the representative of our country. He is a bird of bad moral character. He does not get his living honestly. Besides he is a rank coward: The little king bird not bigger than a sparrow attacks him boldly and drives him out of the district.” And so it turns out that bald eagles are often harassed or chased by their fellow raptors and by songbirds including blackbirds, crows and flycatchers as well.
During breeding season you may see bald eagles defending their territories from a variety of intruders, including raptors and ravens, coyotes and foxes. When feeding at carcasses though, bald eagles may push turkey vultures out of the way, but other species including ravens, coyotes, bobcats and dogs sometimes hold their own.
Bald eagles are powerful fliers. They soar and glide gracefully over long distances. Capable of floating, a bald eagle may use its wings to “row” over water too deep for wading.
Picking a mate and pair-bonding in bald eagles is a fascinating ritual behavior probably few people are lucky enough to witness. They perform aerial acrobatics and in one of several spectacular courtship displays, a male and female fly high into the sky, lock talons, and cartwheel downward together, breaking off at the last instant to avoid crashing to earth. More often, two birds can be observed soaring together or chasing each other. In chases, one bird will chase after the other, usually in a rather shallow glide. It is also not uncommon to see them switch places during chases. They might also be seen passing sticks in mid-air.
Another part of pair-bonding is side-by-side perching. This usually happens in the near vicinity of the nest, sometimes on the nest itself. They may even lie in the nest right next to each other.
Adult bald eagles generally mate for life, but if one of the pair leaves or is killed, the survivor will take another mate. The nest might be abandoned if it is the female that is lost. Whether the birds are taking their first mate, second or third, the process is the same: pair-bonding, nest-building and production of young. A pair may repeat this year after year until the pair is more than 20 years old.
A bald eagle’s nest grows with each year and the nest can grow to more than 6 feet wide and 10 feet deep. The male usually brings nest material to the nest site where the female does the building and arranging. Sometimes the male will pass sticks to the female on a branch near the nest or even between them in mid-air.
Bald eagles generally lay one to three eggs. Females will incubate the eggs about 60 percent of the time. During incubation, the male will bring food for the female; usually to one of the supporting branches of the nest. She will usually come off the eggs to eat, with the male taking her place on the nest. Sometimes the female may hunt for herself while the male takes his turn on the eggs.
During the first 90 days of life, little eaglets grow from a hatch weight of 10 ounces to their adult weight that might reach 12 pounds. An eaglet that is last to hatch in a brood of three may not survive. The older siblings will out-compete the littlest one for food and have been known to shove their way around the nest, sometimes inadvertently killing the youngest. If all siblings survive, it is probably because the parents are in a habitat with abundant food, where feeding themselves and multiple young is possible without causing strife at the nest between the youngsters.
At 12 weeks of age the young will take off from the nest. The first flight is generally short and typically, to a perch lower than the nest site. The landing might be anything but gentle. It takes practice to figure out when to stop flapping their wings while grabbing a perch. The result can, surprisingly often, be a perfect two-point landing, except that the bird ends up upside-down. Injuries rarely occur during these episodes and in just a few tries the young eagles will look like they’ve been landing on tippy branches for years.
For the next four to six years, an eagle’s life is spent hunting and eating. During this time they will probably start forming some sort of a bond with another eagle. Eagles do not reproduce until they are about five years old, and at this time they undergo their final plumage change with the distinctive white head and tail.
Coward or not, the bald eagle is a beautiful, fascinating bird!
Joanne Stolen is retired from teaching microbiology at Rutgers University.