In late summer, the bird spends a great deal of time repairing the nest for use in the following year. Early in the season, a small hollow accomodates the eggs, but the nest grows flatter as the nesting season advances. Each year, the Osprey adds materials, and as a result, the weight of the nest sometimes causes it to slide down the trunk of the tree. Generally, the Osprey defends its territory against other large birds such as eagles, owls, gulls, and the Great Blue Heron, which will not hesitate to take over its nest. The Osprey frequently takes the precaution of building more than one nest in its territory, especially if one year it does not manage to have young.
Some couples share the same nest year after year.
At the start of the breeding season, when they are pairing or reaffirming their bond, they perform a spectacular display. The male repeatedly flies high into the air, hovers for a few seconds, dives, and reascends in a sweeping arc. Sometimes the female participates in a modified version of this display, making a show of pursuing the male. In another type of ritual display near the nest, the male flies laboriously, body arched and feet danging below, often holding a fish or a branch in his claws. According to estimates, nesting females lay an average of three buff-coloured eggs with dark brown speckles.