The hormonal environment during early development, such as maternally derived androgens in bird eggs, has been shown to shape offspring in ways that may have important short- and long-term consequences for phenotype and behavior. However, studies on the effects of androgens on begging behavior and growth in birds have provided variable results and sex-specific effects are not well understood. We experimentally elevated yolk androgen levels in whole clutches in a passerine bird, the pied flycatcher Ficedula hypoleuca and studied effects on male and female begging behavior, ingestion and digestion. Yolk androgen elevation led to shorter latencies to beg in both male and female nestlings but to greater begging rates only in males. Both responses could be used as cues to solicit more food from parents. Yolk androgens had no effect on food intake, fecal wet mass or fecal water content. However, the proportion of organic matter in feces was lower in androgen-treated than control males, potentially suggesting that the androgen-treated individuals had more efficient digestion. We discuss the alternative pathways of effects of yolk androgens on begging, growth and digestion. If the effects of yolk androgens on phenotype and behavior are causally linked, there is less scope for the mother to adjust specific offspring traits independently from other traits. The sex-specific effects of yolk androgens should be studied more, also in within-clutch context, as the costs and benefits for each sex may further differ in relation to hatching order.
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