Saturday, May 21, 2011

Wilson's Phalarope

While we are enjoying a great warbler migration, shorebirds are few and far between.  Too much water this wet spring?  Erika and I did encounter a few Wilson's Phalaropes in southern Dakota County, Minnesota.  The three birds in the foreground of this photograph are phalaropes.  The birds behind them are Lesser Yellowlegs.

Female phalaropes are brighter than their dull-colored males.  In the photograph, a male is in the immediate foreground, with two females behind him.  On their breeding grounds, females compete for males, often breeding with more than one mate (polyandry).  After laying her eggs, the female deserts the male to compete for additional mates, leaving the first male all subsequent nesting duties (incubation, brooding, and other parental care).  

Phalarope endocrinology (hormones) is complicated. In other birds, males usually have high steroid levels, while females have more prolactin (a hormone associated with egg laying and caring for young).  Early studies suggested that male phalaropes have relatively low levels of testosterone, about the same levels as females.  More recent studies show that male phalaropes' testosterone levels spike early in the breeding season, but decline markedly as the season progresses. Prolactin levels in males are stimulated by the presence of eggs or young. Levels rise during incubation and then decline after the young hatch (Colwell and Jehl 1994).

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