Eagles are among the most recognizable birds of prey. While adult eagles are widely known for their distinct features, their offspring, eaglets, undergo a remarkable transformation from hatching to maturity. These young birds look quite different from their parents. Their development presents a fascinating journey. Understanding their changing appearance offers unique insights into their growth.
Newly Hatched Appearance
Immediately after hatching, eagle chicks, known as eaglets, are tiny, measuring only about 4 to 5 inches (10 to 13 cm) and weigh just a few ounces. Their bodies are covered in a thin layer of soft, light gray or whitish natal down, which is often damp and matted at first but fluffs up as it dries. This initial down provides some insulation. At this stage, an eaglet’s eyes are dark brown and open soon after hatching; their beaks and cere, the fleshy part at the base of the beak, are typically gray, while their legs and feet appear pinkish-cream. A temporary, sharp point called an “egg tooth” is present on their beak, which helped them pip open the eggshell and usually disappears within about a week. Eaglets grow rapidly, gaining approximately a half-pound to a pound of body weight every week.
Developing Feathers and Markings
As eaglets grow, their initial downy covering is replaced by a secondary, darker gray down by about two weeks of age. Around three to six weeks, the first true juvenile feathers, also known as contour feathers, begin to emerge. These feathers typically appear first on the wings, back, and breast. Initially, these emerging feathers are very dark, giving the young birds a somewhat spiky or woolly appearance. Juvenile bald eagles leave the nest with predominantly dark brown plumage across their body, often with white flecking on the underside of their wings and belly. Golden eagle chicks develop their characteristic dark brown body and flight feathers, sometimes retaining white patches at the base of their tail and wings. This plumage is distinct from the adult coloration.
Distinguishing Young Eagles from Adults
Differentiating young eagles from mature adults relies on several key visual markers, as their appearance changes considerably over their first few years. Adult bald eagles are recognized by their striking white head and tail, contrasting with a dark brown body, and a bright yellow beak and eyes. In contrast, juvenile bald eagles, for several years after fledging, possess an entirely dark brown head and tail, lacking the distinct white markings of their parents, and their beaks are dark, often blackish, rather than the vibrant yellow of adults. Eye color also indicates age; nestling eagles have nearly black eyes, which gradually lighten to dark brown in juveniles and then to a lighter brown in immature birds, eventually becoming yellow in adults. Golden eagles also exhibit differences, with immatures displaying white patches at the base of the tail and sometimes on the wings, which are typically absent in fully mature adults, and these specific plumage and bare part differences allow for the identification of eagles at various stages of their development.
The Path to Mature Plumage
The transition to characteristic adult plumage is a gradual process spanning several years. Eagles undergo multiple molts, shedding old feathers and growing new ones, which progressively transform their appearance. For bald eagles, this transition to the white head and tail, yellow beak, and yellow eyes typically takes about four to five years. Their plumage evolves through various mottled brown and white stages. Golden eagles also mature slowly, with their final adult plumage, characterized by an all-dark brown body with a golden-brown nape, usually attained between five and six and a half years of age. By the time they achieve full adult coloration, eagles have also reached their full skeletal size.