Every few years a story makes the rounds about a bald eagle carrying off a dog or trying to snatch someone’s cat. Biologists who study birds of prey and folks who live around eagles have seen plenty snatching and carrying – as well as swooping and swimming – and they offered insights into what eagles really can and cannot do.

Bald eagles are strong, aggressive birds but like everything that flies they are governed by aerodynamics. The wings of an eagle need to support the eight to 12-pound bird as well as whatever the bird is carrying, and best estimates put the lifting power of an eagle at four or five pounds. But it’s not quite that simple.

Lift is dependent not only on wing size, but on airspeed. The faster a bird (or plane) is flying, the greater the lift potential. An eagle that lands on the beach to grab a fish, and then takes off again, is limited to a smaller load than an eagle that swoops down at 20 or 30 miles an hour and snatches up a fish. That momentum and speed gives the bird the ability to carry more weight.

Biologist Ron Clarke earned his masters degree studying birds of prey, and he’s a falconer who trains raptors. He hunts with a gyrfalcon and a peregrine falcon, and said his 45-ounce gyr can carry an 8-ounce bufflehead duck pretty easily. “He can't do the same with a mallard, though,” he said. At about two pounds, a mallard is four times the weight of a bufflehead.

Clarke said an eagle with momentum is a different story.

“On a wide-open beach, I have no doubt that an eagle with a full head of steam could pick up a six- or eight-pound dog and just keep on going,” Clarke said. “If it landed to kill a ten-pounder, and then tried to pick up and fly from a dead stop, could it get off the ground? Probably not.”

Eagles will carry heavier loads a short distance. Mike Jacobson spent decades as an eagle management specialist for the U.S. Fish and Wildlife Service and recently retired.

“There used to be stories about eagles carrying off babies and little kids, and none of that has ever been documented,” he said. “They can pick up and carry four or five pounds, maximum, and actually fly off with it. They can lift a little more and hop it along, but they can’t carry it off.”

Flying may be an eagle’s birthright, but it requires skill. Falconers and birdwatchers can attest that swooping down to nab dinner, or snatching food off the water, requires techniques that are honed with experience. Young predators develop their hunting skills by trial and error, play, and testing limits. Young eagles will swoop on floating bottles, attempt to lift salmon that are too heavy, and investigate new objects.

Jacobson said an immature eagle is most likely to swoop down on something inappropriate, like a large dog on the beach. People then overreact and claim that eagles are hunting dogs. “It gets exaggerated” he said. “Eagles don’t hunt cats and small dogs.”

 

 

Read the rest here.