Hormonal Control of Incubation/Brooding Behavior: Lessons from Wild Birds

More than 90% of all bird species are monogamous within a breeding season. Biparental care of eggs and young is generally the rule for these species, especially for those which do not produce precocial young. Thus the common domesticated species differ from the majority of other birds in the display of parental behavior. The hormonal control of such behavior, however, appears to be similar in all birds, with variations associated with different social systems, phylogenetic histories and ecologies. I have studied the correlation between plasma levels of hormones and behavior in free-living birds of several species and found the following general characteristics. Elevated testosterone appears to be incompatible with assiduous parental care in males. Prolactin is highly correlated with the display of both incubation behavior and brooding/feeding of altricial young. In those species in which non-breeders help raise the young of other birds (cooperative breeders), prolactin levels are elevated in the helpers, sometime even before begging young are present. Many seabirds such as penguins leave the eggs and young for many days to forage at sea while the mate remains at the nest. Despite the absence of tactile stimulation, the foraging birds maintain high levels of prolactin and spontaneously return to the nest to incubate. Vasoactive intestinal peptide is a potent prolactin releasing factor in birds including several species of passerines as well as gallinaceous and columbiform birds, but the interaction of the serotonergic systems may differ among species. ___________________________________________________________________________