6533b7d6fe1ef96bd1265d76

RESEARCH PRODUCT

Endocrine correlates of the breeding asynchrony between two Corsican populations of Blue tits (Parus caeruleus)

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International audience; Analyses of the development of the reproductive system in seasonally breeding birds in the framework of long-term ecological studies are rare. Here, we present the Wrst results of such a study in two Corsican populations of a European passerine bird, the blue tit (Parus caeruleus). The two study populations occupy diVerent oak habitats and are separated by only 25km. Despite their close proximity, they show a one-month diVerence in onset of egg laying, even after controlling for altitude. This micro-geographic diVerence in breeding date appears adaptive because both study populations raise chicks when food is most plentiful. In our study, males reached their maximum song activity during the egg-laying stage while maximal testosterone levels and testes sizes were reached 2–3 weeks before egg laying. The rate of development of the reproductive system in males was much faster in the earlier population, in spite of a similar onset of gonad development and song activity for the two study populations. No change in the volume of the songcontrol nuclei (HVC and RA) could be detected during the study period. Development of brain nuclei was completed 2–3 months before the beginning of intense sexual activity.