Golden Eagle

Golden eagles are among the fastest birds of prey, diving at an estimated 240 to 320 km/h (150 to 200 mph) in a hunting stoop. The high-soar vertical stoop is used mainly against birds in flight, usually slower species such as geese and cranes, and it is rarely observed because the eagle needs a height advantage. Eagles have even been recorded catching demoiselle cranes in midair during migration over the Himalayas. Most hunts are less dramatic. Eagles often glide low along the terrain, then surprise hares, rabbits, and marmots with a short, fast attack. Typical unhurried soaring is only about 45 to 52 km/h (28 to 32 mph). This mix of height, patience, and sudden acceleration helps make the golden eagle a top predator across open and mountainous country.

Eagle eyesight is often described as four to eight times sharper than a human’s, though that figure refers to eagles in general rather than golden eagles specifically. Eagle eyes have two foveas, the dense patches of cells that produce the sharpest vision: a deep one that looks to the side and a shallower one that looks nearly forward. The eagle fovea holds roughly one million cells per square millimeter, compared with about 200,000 in humans. An eagle in flight can reputedly spot a rabbit from about 3.2 km (2 mi) away, though that distance is an estimate. For a hunter that scans open mountains, grasslands, and tundra from high above, spotting movement early matters. Once prey is found, powerful feet and sharp talons finish the job.

Golden eagles feed mainly on hares, rabbits, ground squirrels, and marmots, yet more than 400 vertebrate species have been recorded as prey, including over 200 species of birds. They also take reptiles, fish, and occasionally larger animals. Deer make up only about 5 percent of the diet, and most of those are young animals such as fawns. Livestock account for less than 1.4 percent of prey in North America, and many lambs eaten by eagles may have been scavenged already dead. Researchers describe seven main hunting methods, from high soaring stoops and low contour flights to tail-chases and even walking on the ground to grab prey. This flexibility helps explain why the species thrives in such different habitats.

Golden eagles have few natural enemies, but they will defend their young and kills with surprising aggression. They have been seen fighting off coyotes and even bears in defense of prey and young. Wolverines and grizzly bears are the only recorded predators of nestlings, so the risk is real. Breeding pairs share the workload at the nest. The female does most of the incubating and broods the chicks for much of their first 45 days, while the male brings most of the food during the first few weeks. Pairs also sometimes hunt together, with one eagle distracting the prey while the other strikes. Human disturbance can also be costly, since adults are likely to abandon a nest if disturbed during incubation.

Golden eagles form long-term pairs, often for life, and non-migratory pairs appear to stay together year-round. Each pair defends a territory, typically 20 to 200 km² (8 to 77 sq mi), and guards its boundaries with flight displays. The size varies with the landscape, from as little as 1.5 to 9 km² (0.6 to 3.5 sq mi) in Ethiopia’s Bale Mountains. Pairs in the western United States typically defend 20 to 33 km² (8 to 13 sq mi). Within that range, a pair builds several nests, called eyries, and uses them in turn over the years. Nests are usually on cliffs, and both partners help build or refurbish them. Because pairs reuse and refurbish their nests season after season, some grow enormous, with the largest recorded standing 6.1 m (20 ft) tall.

Outside the pair bond, golden eagles are highly solitary, hunting and roosting alone rather than in flocks. Juveniles become independent in the fall and then wander widely. In a Scottish tracking study, young eagles began dispersing between 39 and 250 days after fledging, and every one of the 24 tracked birds had left its home range within its first year. Most made exploratory trips of up to 44 km (27 mi) before leaving. Young eagles typically establish a territory at about four to five years old. Gatherings are rare and tied to extreme cold or abundant food, though 124 eagles were once seen perched along 85 power poles in eastern Idaho on a cold night. This spread-out lifestyle suits birds that need large hunting territories.