Relationships between the daily variations of social behavior and of plasma FSH, LH and testosterone levels in the domestic duck Anas platyrhynchos L.

The daily variations of plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone were studied in three groups of 10-12 male domestic ducks at different times in their reproductive cycle. Rapid and significant changes in the mean plasma hormone levels were observed in each case but no reproducible pattern of daily variation could be defined. Before being submitted to repeated blood sampling, the birds were observed for their social behavior on several days from dawn to dusk. The frequencies of social displays and sexual behavior also changed significantly during the day but, once again, the pattern of changes was different from one case to another. There was, however, some indication that the pattern of daily changes could be a function of the season. The study of the relationships between the daily changes in behavior and in plasma hormone levels revealed several significant positive correlations. The variations in plasma FSH and/or testosterone are correlated with the variations in social displays and sexual behavior. Furthermore the same correlations could be detected in different groups of animals which had otherwise completely different patterns of daily variations. This suggests that the short-term changes in behavior could be controlled by these hormones, but it is still unclear whether the changes in hormone levels can cause behavioral changes within hours rather than the converse.