The neural and hormonal basis of parental behavior has been studied extensively in both
domesticated and free-living birds of many species, although there is no clear understanding of
how the diversity in parental behavior arises from the underlying physiological mechanisms
(reviewed in Buntin, 1996). Much of the work on free-living birds has focused on the correlations
between plasma levels of the hormone prolactin and parental behavior, and how these vary with
social system, ecology and life-history traits. In contrast, much of the work with domesticated
species of economic importance has focused on the hypothalamus-pituitary axis and the
secretion of prolactin, with the general goal of understanding how broodiness can be inhibited in
order to prevent egg production losses that accompany broodiness. Many of these poultry
species have been artificially selected for precocial maturation, high egg production, reduced
seasonality, and reduced broodiness. In addition, parental behavior of galliform birds is atypical
because the chicks are precocial, requiring relatively little parental attention, and because the
males provide little or no parental care. Another well-studied group, the Columbiformes, provide
biparental care, but doves and pigeons secrete prolactin to stimulate maturation and secretions of
the highly specialized crop gland, an adaptation for providing nutrition to the hatchlings that is
not found in any other order of birds. Thus, control of prolactin secretion and parental behavior
in these domesticated species could differ from that in the majority of other bird species.