Penguins generally return to the same colonies year after year, where they seek nest sites and mates. Males usually return to the colony first, followed shortly after by females. For the four subtropical and tropical species the Galapagos, jackass, Magellanic, and Humboldt penguins this means returning to underground burrows, cracks, or caves that shelter nesting pairs from the scorching sun and land-based predators. These birds nest at any time of year, depending upon food availability. The fiordland penguin nests under tree roots in coastal rainforests off New Zealand.
Recognition is key for a pair's survival and the survival of their offspring.
Pair bonds form quickly, and mates recognize each other by wing-flapping, neck raising, and other displays. Such exuberance is contagious. Often when one pair starts to greet, the excitement ripples through the colony, as if the birds are doing a strange form of the wave. On such open colonies, nests consist of scraped depressions lined with small rocks, bones, or grasses. Pairs often fight over stones, precious nesting materials that are regularly stolen by neighbors.