Prolactin and parenting in the pigeon family.

The relationship between plasma prolactin and: crop growth; incubation; brooding; and feeding young in Columbiformes is reviewed. There is a good parallel between changes in crop growth and plasma prolactin fluctuations during the breeding cycle. Prolactin does not play a role in the initiation of incubation, though it can maintain the response. Toward the end of breeding, a decline in prolactin precedes the decline in incubation (of infertile eggs) or brooding (of young), while exogenously administered prolactin can prolong the response. There is no evidence of a necessary relationship between prolactin secretion and parental feeding of young, as this behavior can precede and outlast the secretion of the hormone during breeding.