Stolen: The bald eagle: One powerful bird |

Stolen: The bald eagle: One powerful bird

Dr. Joanne Stolen

We saw an osprey dive bombing a bald eagle in Pirates Cove on Dillon Reservoir recently. At first, the bald eagle just seemed to flinch, but the persistent osprey finally got him to leave his perch and fly away. One would think this rather unusual, since the bald eagle is usually larger and more aggressive than an osprey.

The name “bald eagle” comes from the word “piebald,” and refers to the white head and tail feathers. It is a powerful flier, and soars on thermal convection currents. It reaches speeds of 35-43 mph when gliding and flapping, and about 30 mph while carrying fish. Its dive speed has been clocked between 75-99 mph, though it seldom dives vertically. Their diet varies from fish to carrion to small animals and birds. They have been known to even attack birds as large as the great blue heron. They also may scavenge from campsites and garbage dumps. Fish are their most important live prey. They swoop down, snatch the fish out of the water, and eat by grasping the fish in one claw and tearing the flesh with the other. Eagles have structures on their toes called spiricules, which allow them to grasp fish.

Bald eagles reach maturity at about four years of age, and they often return to the area where they were hatched to mate. It is thought bald eagles mate for life. Bald eagle courtship involves a variety of calls and flight displays, which includes chasing, swooping and cartwheels. They fly high, lock talons, and free fall, separating just before hitting the ground. They can produce up to three eggs, but all three chicks seldom survive. The nest is the largest of any bird in North America; it is used repeatedly over many years, and they may add new material each year. The nest may eventually become 13 feet deep, 8 feet across and weigh 1 ton. The wingspan of the bald eagle may reach 8 feet, and females are generally larger than males and can weigh up to 15 pounds! In the wild they live about 20 years, but a captive eagle lived nearly 50 years. Bald eagle populations have been affected by oil, lead and mercury pollution, and by human and predator intrusion. Like many birds of prey, eagles were especially affected by DDT. The bald eagle was declared an endangered species in the U.S. in 1967, but the population rebounded, and was taken off the endangered species list in 1995.

This much-photographed bird of prey is our national symbol. It appears on most official seals, including the Seal of the President of the United States. The Continental Congress adopted the current design for the Great Seal of the United States, including a bald eagle grasping 13 arrows, and a 13-leaf olive branch with its talons. It seems the founders of the United States were fond of comparing their “new republic” with the Roman Republic, in which eagle imagery was popular. Legend has it that, during one of the first battles of the Revolution, the noise of the struggle awoke the sleeping eagles on the heights, and they flew from their nests and circled over the heads of the fighting men. “They are shrieking for Freedom,” said the patriots.

The bald eagle is also a sacred bird in many North American cultures, and its feathers, like those of the golden eagle, are central to many religious and spiritual customs among Native Americans. Eagle feathers are often used in traditional ceremonies, particularly in the construction of regalia worn and as a part of fans, bustles and head dresses.

In Summit County, bald eagles are occasionally spotted on Dillon Reservoir, but it’s more common to see them downvalley toward Heeney and Green Mountain Reservoir.

Breckenridge resident Dr. Joanne Stolen is a former professor of microbiology from Rutgers now teaching classes at CMC. Her scientific interests are in emerging infectious diseases and environmental pollution.

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