Social competition and plasma testosterone profile in domesticated canaries: an experimental test of the challenge hypothesis.

The challenge hypothesis predicts that plasma testosterone (T) concentration is high when male-male competitions are high and decreases when males are engaged in paternal care. In monogamous species, T concentration increases at the beginning of the breeding period and decreases after egg laying. According to the challenge hypothesis, increasing competition should also lead to T increase.

Sexually attractive phrases increase yolk androgens deposition in Canaries (Serinus canaria).

The androgen concentration in birds' eggs varies with laying order, breeding conditions, and mate attractiveness. In passerine birds, mate attractiveness depends upon song quality. The aim of our study was to evaluate the effect of one criterion used by females to assess male song quality that is to say the presence of sexually attractive phrases on yolk androgen deposition.