In May eagle chicks are hatching in nests all over Rocky Mountain National Park. The park is home to an estimated ten mated pairs of golden eagles. These magnificent birds favor wilderness areas and are more common in the west than in the eastern United States. There is also one pair of bald eagles that nest just outside the park on United States Forest Service land. Immature eagles take four years to reach adult plumage, mate for life, but will re-mate if one of the pair dies. Eagles are migratory, and migrate independently of their mates. During the winter, bald eagles may gather in large numbers where big concentrations of fish make for easy pickings. Unlike the bald eagle, golden eagles are solitary or observed in pairs. Generally the male of the pair arrives first in the spring and claims a territory. A breeding pair may alternate between several nests in different years. An eagle eyrie is a large mass of sticks on a crag or ledge or occasionally in trees. In Europe and the United States some golden eagle eyries are known to have been used continually by successive generations for centuries.
Once the female arrives, the pair starts to prepare the nest by adding new sticks and pine boughs. Most pairs have several nests within their territory and may appear to start nesting in more than one in the spring. This may well be a means to deter predators from finding the nest they will actually use. Eagles may use the same nest for a few years and then move to a new one, or may change nests more frequently. This may also be a strategy to fool predators, as well as a way to escape parasites that may have also inhabited last year's nest.
Eagles generally lay two whitish, blotched eggs a few days apart, but start incubation as soon as the first egg is laid. This results in one eagle chick hatching before its sibling, and thus being larger. Because success of the brood is dependent on the parents finding enough food for the chicks, in most years only one chick survives. It is usually the larger chick that competes best in getting food from the adults, and it may even push its sibling out of the nest in order to get all the food brought by the adults. As harsh as this may seem, it is an efficient way to ensure the strongest chick survives. In years when food is abundant, the eagle pair are often able to fledge both chicks. Adults feed their young a variety of prey, but the remains of common species found in nests within the park include, yellow-bellied marmots, Abert’s and Wyoming groundsquirrels, rabbits, and even the remains of bighorn sheep lambs. Mid-May is a wonderful time to see these fuzzy, but intense "snowball" chicks and watch a drama of nature take its course in Rocky Mountain National Park.