WITHIN-CLUTCH VARIATION IN YOLK ANDROGENS IN RELATION TO FEMALE EXPRESSION OF A MALE ORNAMENT IN PIED FLYCATCHERS FICEDULA HYPOLEUCA

SUMMARY.—Within-clutch variation in yolk androgens in relation to female expression of a male or-nament in pied flycatchers Ficedula hypoleuca. Aims: Female birds deposit variable amounts of androgens in their eggs, and research shows that these hormones can influence several aspects of offspring development and phenotype. Some evidence sug-gests that yolk androgen deposition may be a costly investment for the female bird. We studied the rela-tionship between female expression of a male ornament and yolk androgen deposition in the pied flycatch-er Ficedula hypoleuca. In this species, some females present a white forehead patch, which is an ornament typically restricted to males. Female expression of this trait has previously been found to be associated with older age and low levels of blood parasites. We predicted that, if yolk androgen deposition is costly, eggs from females displaying a white forehead patch should contain higher concentrations of yolk an-drogens that those laid by females lacking that ornament. Location: La Hiruela, central Spain. Methods: We measured testosterone (T) and androstenedione (A4) levels in 10 pied flycatcher broods, after an ether extraction, following a radioimmunoassay method. Results and Conclusions: We found that yolk T and A4concentrations increased with laying order