Trade-off between sexual activities and parental care: an experimental test using handicapped mates

Electing to invest in parental care is an adaptive decision thought to involve a trade-off between remating and continuing parental effort. The rock sparrow, Petronia petronia, is an unusual species in which parental investment is highly variable and both sexes may desert the brood. Males contemporaneously engage in parental care, mate guarding, and courting their current or new females. In this study we experimentally handicapped male rock sparrows during the nestling period by increasing their body mass in order to study the effects on male behaviour and the female response. Handicapped males exhibited lower sexual activity than control males but handicapped males did not reduce their offspring feeding rates. Females with a handicapped partner significantly increased the number of sexual soliciting postures towards their mates compared to females paired with control males. The females' behaviour is probably a response to the sexual behaviour change of their partners. Our results suggest that with choices involving a trade-off between mating investment and parental investment, handicapped males chose the parental investment option.