Dynamics of biparental care in house sparrows: hormonal manipulations of paternal contributions

Testosterone (T) is generally regarded as a proximate mediator of avian male trade-offs between mating effort and parental effort, based partly on findings that exogenous T reduces male parental provisioning of nestlings in many passerines. We examined whether T has similarly disruptive effects on male incubation behaviour. We observed behaviour of male house sparrows, Passer domesticus, that were experimentally maintained at high T levels during incubation; we also compared the responses of the males' social mates to deficiencies in the incubation and nestling provisioning contributions of their partners. During the incubation stage of the nesting cycle, T-males spent less than half as much time incubating as control males; in lieu of incubating, T-males engaged in advertisement calling and aggressive interactions more frequently, and were away from the nest more often, than control males. We detected no significant effect of T on male rates of sexual interaction or contributions of nesting material, however. As expected, T-males also provisioned nestlings at lower rates than control males. In turn, females paired to T-males significantly increased their own contributions to incubation, but did not compensate for their mates' reductions in nestling provisioning. These results show that suppressive effects of T on male parental care generalize to incubation behaviour in this species and reinforce the view of T as a mediator of trade-offs between parental and mating effort. In addition, they demonstrate that the existence of any adjustments of parental effort in response to partner contributions can hinge on the form of parental care considered. (C) 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.