The Energetics of Parenting in an Avian Model

Parenting is an energetically costly activity in both birds and mammals, but differences in avian and mammalian modes of reproduction profoundly shape the types and temporal patterns of energy expended in the parental effort. In contrast, birds have an oviparous mode of reproduction that requires parental behavior to be expressed both before and after the young appear if the reproductive effort is to be successful. During incubation, parent birds must actively defend the nest, keep the eggs warm, and turn the eggs periodically to ensure continued embryonic development. After hatching, avian parents typically protect the nest and young from intruders, engage in brooding behavior to provide heat for the nestlings, and provide food for the growing young. Studies of wild bird populations indicate that parents that rear altricial young typically exhibit elevated levels of plasma prolactin when they are provisioning their offspring. For example, prolactin levels in blood correlate positively with the frequency of parental feeding visits to the nest in male house finches, and female red-eyed vireos show higher levels of plasma prolactin, and more parental provisioning, than their male partners. In addition to stimulating crop milk formation in dove parents of both sexes, the prolactin that is secreted into the blood during incubation and the posthatching period is likely to act at both central and peripheral target sites to stimulate the transfer of milk to the nestlings by regurgitation.