Turning a deaf ear: a test of the manipulating androgens hypothesis in house wrens

The manipulating androgens hypothesis (MAH) proposes that female birds increase the level of testosterone (T) in their eggs to promote greater offspring begging, and thereby elicit increased provisioning by their mates. We examined the effect of a positive in ovo manipulation of T on provisioning by house wren, Troglodytes aedon, parents, and concomitantly examined the begging response of nestlings. We also examined the mass of nestlings throughout their growth to assess the effect of T on their development, and three measures of nest performance: hatching success, nestling survival and the proportion of nestlings that fledged. Nestlings hatching from T-injected eggs begged more than nestlings hatching from control (oil-injected) eggs early in the nestling period, but not later in the nestling period. However, treatment had no effect on the levels of parental provisioning or nestling mass gain, nor any effect on hatching success or nestling survival. There was a significant increase in parental provisioning rate, but a decline in the size of prey taken to the nest over the course of the breeding season, which was likely the result of declining environmental quality. Our results support neither the MAH, nor the expectation that nestlings should grow at different rates in relation to in ovo titres of T.