Why do experienced birds reproduce better? Possible endocrine mechanisms in a long-lived seabird, the common tern.

• Published in: General and Comparative Endocrinology
• Main Authors: Riechert, Juliane, Chastel, Olivier, Becker, Peter H
• Other Authors: Institute of Avian Research, Centre d'études biologiques de Chizé (CEBC), Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2012
• Subjects: envir; psy; Common tern; Sterna hirundo
• Online Access: https://doi.org/10.1016/j.ygcen.2012.06.022; https://hal.archives-ouvertes.fr/hal-00721790

International audience The influence of age or breeding experience on reproductive success in vertebrates is well known but physiological mechanisms came into focus just recently. Assessing hormone levels could allow insights into these mechanisms and reproductive strategies in long-lived species. Prolactin and corticosterone are two hormones involved in breeding decisions: high prolactin values are necessary for expressing breeding behavior whereas corticosterone is related to activity or stress. We analyzed baseline prolactin and corticosterone under field conditions in common terns (Sterna hirundo) between 2006 and 2010. We took 760 blood samples of 346 known birds 9-14days after their clutch completion, obtained via blood-sucking bugs (Dipetalogaster maximus), a non-invasive method with negligible stress for the birds. Many individuals were sampled repeatedly during the study period allowing investigation of hormone change on individual level. Prolactin levels increased during the early breeding career, which was confirmed on individual level, whereas corticosterone levels increased mostly in experienced birds, more pronounced in males. Low hormone levels during the first years of breeding could indicate a reduced ability of the endocrine system to secret hormones or it might express a down-regulation to limit parental expenditure. Higher corticosterone values of males could be related to increased foraging activity. Amongst the oldest birds, prolactin seemed to increase in males but not in females. This possible consequence of female senescence might be compensated by high values of male mates. Body mass showed only a weak positive correlation with prolactin level and no correlation with corticosterone concentration.