They are monogamous and may remain together for several years or possibly for life. Golden Eagles nest in high places including cliffs, trees, or human structures such as telephone poles. They build huge nests to which they may return for several breeding years.
Golden Eagle is a large, dark brown raptor with broad wings. Its size is variable: it ranges from 66 to 100 cm (26 to 39 in) in length and it has a typical wingspan of 1.8 to 2.34 m (5.9 to 7.7 ft). In the largest race (A. c. daphanea) males and females weigh 4.05 kg (8.9 lb) and 6.35 kg (14.0 lb). In the smallest subspecies (A. c. japonensis), the sexes weigh, respectively, 2.5 kg (5.5 lb) and 3.25 kg (7.2 lb). The maximum size of the huge eagles is a matter of some debate, although captive birds have been measured to a wingspan of 2.81 m (9.2 ft) and a mass of 12.1 kg (27 lb). Sexes are similar in plumage but are considerably dimorphic in size, with females rather larger than males. Adults are primarily brown, with gold on the back of the crown and nape, and some grey on the wings and tail.
Golden Eagles usually mate for life. They build several eyries within their territory and use them alternately for several years. These nests consist of heavy tree branches, upholstered with grass when in use. Old eyries may be 2 metres (6.6 ft) in diameter and 1 metre (3.3 ft) in height, as the eagles repair their nests whenever necessary and enlarge them during each use. If the eyrie is situated on a tree, supporting tree branches may break because of the weight of the nest.
The eggs vary from all white to white with cinnamon or brown spots and blotches. They start incubation immediately after the first egg is laid, and after 40 to 45 days the young hatch.[citation needed] They are covered in fluffy white down and are fed for fifty days before they are able to make their first flight attempts and eat on their own. In most cases only the older chick survives, while the younger one dies without leaving the eyrie. This is due to the older chick having a few days' advantage in growth and consequently winning most squabbles for food. This strategy is useful for the species because it makes the parents' workload manageable even when food is scarce, while providing a reserve chick in case the first-born dies soon after hatching. Golden Eagles invest much time and effort in bringing up their young; once able to hunt on their own, most Golden Eagles survive many years, but mortality even among first-born nestlings is much higher, in particular in the first weeks after hatching.
