Plasma testosterone levels of incubating black-tailed gulls

In some avian species, male plasma testosterone levels are maximum during the courtship or copulation periods, but decline abruptly once incubation starts. However, testosterone levels of male Black-tailed Gulls Larus crassirostris during the course of breeding remain unknown. In 2006, blood samples of 23 incubating males were collected at Rishiri Island, Hokkaido, Japan and testosterone was measured by enzyme immunoassay kit. Plasma testosterone level (mean±S.E.: 0.737±0.282 ng/ml) was assumed to decline with elapsed days from the onset of incubation, as shown in other species.