Circulating prolactin of incubating male Wilson's Phalaropes corresponds to clutch size and environmental stress

We measured the effect of clutch-size changes on levels of circulating prolactin (prl) among incubating male Wilson's Phalaropes in order to identify the influence of clutchsize as an exogenous determinant of circulating prl, and to better understand the endocrinology of clutch abandonment. One year of the study was characterized by unusually high temperatures and drought, and incubating males appeared to be heavily stressed based on ambient temperatures and rates of weight loss. We used the contrasting environmental conditions between years to compare levels of circulating prl among males experiencing different levels of environmental stress. We found a strong inter-year effect, with significantly lower prl during the high stress year. We also found a clear effect of clutch-size on level of circulating prl during the low stress year of the study. Males with increased or decreased clutch-size had lower levels of circulating prl than did control males. Because prl levels were so variable, we sought alternative explanations to year and clutch-size effects. We examined nine environmental and physiological factors a posteriori for a relationship with circulating prl. Although we identified weak correlates, none of the additional factors could account for the variation in prl explained by year and clutch-size. Incubating male Wilson's Phalaropes appear to experience an adaptive endocrine change when the potential fitness of their clutch is compromised.