Response of testosterone and corticosterone plasma levels to the challenge of sibling competition: a study in common terns.

The hormonal response to social challenges has been widely studied, however, most work focused on adult behavior in a reproductive context although developing animals also encounter important social challenges early in life. We studied the relationship between acute sibling competition and plasma corticosterone (CORT) and testosterone (T) in common tern (Sterna hirundo) chicks, a species whose young compete for access to food by scramble interactions. Blood samples were taken in nests with two and only one single chick both immediately after a feeding bout and in non-challenged controls.

Body condition, hormonal correlates and consequences for survival in common tern chicks.

Although sibling competition in avian species has been extensively studied, the proximate mechanisms remain largely unknown. Recent research proposed that steroid hormones, in particular testosterone (T) and corticosterone (CORT), might play a role either in promoting competitive behavioral displays or in response to chronic nutritional stress accompanied by a sustained competitive situation. Here, we examine body condition, endogenous T levels and fecal glucocorticoid metabolites (FGM) as non-invasive measures of CORT in sibling broods of wild common tern chicks (Sterna hirundo) during three post-natal developmental stages.

Timing of initial arrival at the breeding site predicts age at first reproduction in a long-lived migratory bird.

In long-lived vertebrates, individuals generally visit potential breeding areas or populations during one or more seasons before reproducing for the first time. During these years of prospecting, they select a future breeding site, colony, or mate and improve various skills and their physical condition to meet the requirements of reproduction. One precondition of successful reproduction is arrival in time on the breeding grounds.