The blue-footed booby's distinctive feet play an important role in their famous courtship ritual. The male advertises himself with a special "skypointing" display and, once he has attracted a female, alternately raises one foot and then the other. Next, the female and the male take turns posing in either the skypointing or "bill-up-face-away" posture, until their actions become simultaneous. After mating, one to three eggs are laid and incubated alternately by both parents for about 46 days. After mating, the booby's strange behavior continues with ritual nest-building, which actually serves no practical purpose. When the female is ready to lay, the existing nest is scraped away so she can nest on bare ground. Even more peculiar is the characteristic ring of guano (excrement) that is squirted in a ring around the nest area. Should a chick wander outside this area it will no longer be treated as offspring by the parents. This behavior may have evolved to prevent parents from raising another's young.