Plasma LH and steroid hormones in King penguin (Aptenodytes patagonicus) during the onset of the breeding cycle.

Temporal changes in plasma levels of luteinizing hormone (LH), testosterone, estradiol, and progesterone were measured throughout molt and the onset of reproduction in free-living male and female King penguins (Aptenodytes patagonicus) at Crozet Island (46 degrees S, 51 degrees E). In both sexes, LH concentrations began to rise as soon as molting ended, before the departure for refeeding at sea, suggesting that the beginning of reproductive activity is not associated with refeeding and/or courtship behavior. LH remained at high values throughout courtship and decreased to lower levels during incubation. Gonadotrophin secretion covaried with sustained plasma testosterone levels in males and increased estradiol and progesterone levels (peaking at copulation) in females.