Bald Eagles Information Continued
Bald eagles are large, dark birds; an adult (four or five years old) has a completely white head and tail. Immature bald eagles show varying amounts of white and they can be mistaken for golden eagles. Habitat can be a clue to which eagle you are seeing. Bald eagles are usually near water where they feed on fish and waterfowl. They also nest in large trees close to water. Golden eagles hunt in open country for rabbits and other small mammals. Both types of eagles feed on carcasses in the winter, sometimes together. Females are larger than males, as is true with most predatory birds. Report a sighting of this species.
Bald eagles, which may reuse the same nest year after year, occupy territories near the park’s major rivers and lakes. Juveniles may migrate to warmer habitats like western Oregon and Washington in the fall, but adults often stay in the park year-round. Winter populations increase when bald eagles that breed farther north migrate here. In severe winters, eagles may move to lower elevations such as Paradise Valley, north of the park, where food is more available. On these wintering areas, resident eagles may be joined by migrant bald eagles and golden eagles.
Bald eagles form long-term pair bonds. The female lays two to three eggs (usually two) from February to mid-April. Both adults incubate the eggs, which hatch in 34 to 36 days. At birth, young (eaglets) are immobile, downy, have their eyes open, and are completely dependent upon their parents for food. They can fly from the nest at 10–14 weeks old. The number of eaglets that fledge each year depends partly on weather and can fluctuate widely.
More than half of the park’s known bald eagle nests have been in the Yellowstone Lake area, where the productivity and success rates are generally much lower than in the rest of the park. However, in 2012 nest success and productivity were the same for both areas, about 64 percent.
Research has shown that human presence can disturb eagle nesting and foraging, therefore nest areas in national parks may be closed to visitors. Yellowstone manages nest sites on a case by case basis. In 2010 and 2011, a raptor program documented 22 raptor species in Yellowstone. Bald eagles were the second most commonly reported species (13%) after red-tailed hawks (28%). A recent study found little evidence to support the claim that cutthroat trout declines have resulted in lower nesting success for bald eagles on Yellowstone Lake. Bald eagles, like osprey, are among the fish-eating wildlife being monitored to determine any effect from the declining cutthroat trout population.