The role of prolactin in parental care in a monogamous and a polyandrous shorebird.

We compared circulating prolactin levels in two species of shorebirds which have very different social systems, and which breed sympatrically at La Perouse Bay, 40 km east of Churchill, Manitoba. Semipalmated Sandpipers (Calidris pusilla) are monogamous and share incubation equally, although females normally desert broods earlier than males. Rednecked Phalaropes (Phalaropus lobatus) are facultatively polyandrous, and only males care for eggs and young. High prolactin values were correlated with persistent incubation behavior in male Rednecked Phalaropes, and male and female Semipalmated Sandpipers. Prolactin levels in Semipalmated Sandpipers increased dramatically at the onset of incubation, and were not different between the sexes. Incubating male phalaropes had greater prolactin values than the non-incubating males and females. Changes in prolactin levels, however, did not explain the early brood desertion of female Semipalmated Sandpipers. Prolactin levels did not decline with age of brood in either sex of this species. Received 16 October 1989, accepted 29 April 1990.