nest building
a form of parental behavior, observed mainly in fish, birds, and nonhuman mammals, that involves finding and preparing a site for laying eggs or giving birth to young. The forms of nest building vary widely, but generally all are associated with hormonal activity induced in the female by changes in day length, temperature, courtship with a male, or the presence of offspring. In species with biparental care, such as many monogamous birds and rodents, nest building may be done by both sexes. In some fish, males are the exclusive nest builders. Nest building in nonpregnant female mammals can be induced by exposure to young animals (see concaveation).