How to tell the difference between North America’s two largest raptors
by Lisa Densmore
t appeared as if Rudolph Jr. had misjudged his take-off and met his demise. The young deer entangled in live power lines short-circuited not only himself, but also East Missoula. The incident and ensuing power outage in June 2011 made international news. Contrary to headlines like “Deer with Wings Dies in Power Lines,” the deer could not fly. An avian predator most likely dropped it there. A bystander who observed and photographed a bald eagle in a nearby tree about the time of the power outage surmised that the eagle had nabbed the fawn in its talons, then dropped it onto the power lines when it proved too heavy to carry aloft. News services ran with the unsubstantiated theory. Could a bald eagle kill and transport a baby whitetail? Possibly, but on the rare occasion when a bald eagle kills a small fawn, it typically eats it where the kill was made. Bald eagles don’t normally hunt venison; they generally prefer fish. Golden eagles, on the other hand, do prey on ungulates, in addition to rabbits, squirrels and prairie dogs. Golden eagles and bald eagles differ in more than their preference for deer or trout. Goldens are prairie birds accustomed to grasslands and arid, cliffy habitats. Baldies seek riparian areas and lakes where they can fish, or just as likely steal fish from other birds of prey.
A bald eagle will bully an osprey until it drops its prize, then catch the falling piscis and wing away with it. As a result of their fish-based diet, bald eagles became poster-birds in the mid-20th century for the effects of dichlorodiphenyltrichloroethane, or DDT, on eggshell density. DDT was used as a pesticide to control mosquitoes and insects, and washed into nearby waterways, where fish absorbed it. Bald eagles were poisoned when they ate the fish. America’s national bird neared extinction, but has since recovered. DDT didn’t affect golden eagles, but goldens have recently suffered population declines due to habitat change resulting from drought. While no one is certain how the “deer with wings” ended up on the power lines, both golden eagles and bald eagles have a reputation for getting zapped by wires. When a bird’s wings or feet touch two lines at once, forming a circuit, the bird fries. Since the 1970s, as a result of avian electrocutions, utility companies have modified poles and power lines in rural areas to make them more raptorfriendly. But power lines in urban areas are retrofitted only on a pole-by-pole basis as old ones are replaced over time. It takes four to five years for either eagle species to mature. During that time an immature bald eagle, which lacks a white head, closely resembles an immature golden eagle. The key to telling the difference is the beak. Goldens have a smaller, blueblack beak with a nearly black tip, while baldies’ are yellow. Once mature, goldens generally grow longer (up to 40 inches) than bald eagles (up to 37 inches), though bald eagles have a slightly broader wingspan (up to 90 inches, versus 88 inches). Both weigh between 9 and 10 pounds. While goldens and baldies are the two largest raptors in North America, and both are called “eagles,” they aren’t closely related. Golden eagles (Aquila chrysaetos) are one of only three American hawk species, along with rough-legged hawks and ferruginous hawks, to have feathers all the way to their feet. They’re a member of the booted, or true, eagle family, most closely related to red-tailed hawks. Bald eagles (Haliaeetus leucocephalus) are in the same genus as sea eagles. In Montana, there are plenty of opportunities to observe these two raptors, but perhaps none better than the annual Bridger Raptor Festival at Bridger Bowl, in Bozeman. Each fall, during the hawk and eagle migration along the crest of the Bridger Mountains, thousands of eagles wing their ways south from Canada. Citizen scientists from around the state join professional researchers counting the birds as they fly over Bridger Bowl’s summit. None of the observers have reported an eagle carrying a deer—at least not yet.