THE VALUE OF MALE PARENTAL CARE AND ITS INFLUENCE ON REPRODUCTIVE ALLOCATION BY MALE AND FEMALE DUNNOCKS

1. The variable mating system of the dunnock enabled us to measure how different amounts of male help influenced reproductive success. Male help became increasingly valuable as brood size increased, but the addition of one male's help increased success more than the addition of a second male's help. 2. Removal experiments confirmed that differences in reproductive success were caused by differences in male help. 3. Females laid a larger clutch when they expected two males' full-time help than when expected male help was less. 4. We used data on the value of male care to predict how males should allocate their effort between two synchronous broods. As predicted: (a) a polygynous male preferred to invest full-time in one brood rather than part-time in both, (b) in polygynandry, where two males shared two females, each male preferred to feed at different nests rather than to both help one brood and leave the other unaided. 5. In polygynandry, a male chose to feed the brood of the female with whom he had gained a greater share of the matings (and hence paternity). However, mating share did not influence the provisioning rate of a lone male helping a female, he worked equally hard whether he gained all or just a share of the matings. 6. Males preferred mating to chick feeding and, with two fertile females, spent most time with the female closest to laying. 7. We conclude that with choices involving trade-offs between two mating efforts, two parental efforts, or mating versus parental effort, males chose the option which led to greatest reproductive success.