Hormonal correlates of polyandry in the spotted sandpiper, Actitis macularia

Plasma samples from naturally breeding populations of spotted sandpipers, Actitis macularia, were analyzed by radioimmunoassay for circulating levels of immunoreactive luteinizing hormone (irLH), and four steroid hormones. Plasma levels of irLH, corticosterone (C), and estradiol-17 beta (E) did not differ between males and females. Males had curiously high levels of E (0.64 pg/ml in nonnesting males; 0.35 pg/ml in nesting males) which are similar to those of nonlaying females (0.23 pg/ml). Testosterone (T) and dihydrotestosterone (DHT) were higher in nonnesting males (0.95 ng/ml for T; 0.20 ng/ml for DHT) than in females (0.18 ng/ml for T; 0.12 ng/ml for DHT) or nesting males (0.17 ng/ml for T; 0.09 ng/ml for DHT). These data do not support earlier suggestions that in polyandrous mating systems, females have higher circulating levels of androgens than males.