A bird nest is the spot in which a bird lays and incubates its eggs and raises its young. It is the knot-hole left by a broken branch. Although nests are primarily used for breeding, they may also be reused in the non-breeding season for roosting and some species build special dormitory nests or roost nests or winter-nest that are used only for roosting. Most birds build a new nest each year, though some refurbish their old nests. In most species, the female does most or all of the nest construction, though the male often helps. In some polygynous species, however, the male does most or all of the nest building. The nest may also form a part of the courtship display such as in weaver birds. The ability to choose and maintain good nest sites and build high quality nests may be selected for by females in these species.