Many male birds use brightly colored feathers to show off to females during the breeding season. Most males set up territories containing important resources (food, nesting materials), and try to attract females while keeping males out. Courtship can be an elaborate affair, with displays by the male and sometimes by females, depending on the species. After mating, all birds lay eggs. As the egg develops, the yolk gets covered with layers of egg-white (to feed the embryo), shell (for protection), and pigment (for color). Eggs must stay at the right temperature for development. Most birds incubate their eggs by sitting on them so that they touch a warm, bare spot of skin on the parent (brood patch). Parental care of hatchlings tends to be intensive, with one or both parents feeding the young. Hatchling birds have a lot to learn (the parents' song, the location of feeding areas, migration routes).