The distinctive adult colouration is not attained until their second full spring. Their underparts are white with grey-black streaks and more numerous, finely vermiculated grey lines. The eyes colour of immature birds is a deep yellow and is vermilion red in adults. Northern goshawks are monogamous and mate for life. They are territorial and, if left undisturbed, will return year after year to the same general area to breed.
Nests are large, bulky, and constructed of coarse sticks and smaller twigs.
May. The eggs are incubated by the female for 36 to 41 days. Young begin to hunt on their own about 50 days after hatching and are independent by about 70 days of age. Throughout the nesting period, fresh evergreen sprigs may be added to sanitize the nest. Some researchers have speculated that this behaviour may ward off parasites and biting insects that bother the young. The same nest may be used over several consecutive nesting seasons with only minor repairs, or two or three additional nests may be constructed nearby in the same breeding territory and used in alternate years.