PROVISIONING OF NESTLINGS BY MALE AND FEMALE RED-WINGED BLACKBIRDS, AGELAIUS-PHOENICEUS

Stepwise multiple linear regression was used to identify the factors that affect the rate at which nestlings were fed by male and female red-winged blackbirds, and the effects of this provisioning on reproductive success. In addition, discriminant function analysis was used to examine the differences between pair-fed and female-fed broods. Both maternal and paternal feeding rate were found to increase with breeding experience, brood size, proportion of males in the brood and nestling age. The male was most likely to feed nestlings in the most advanced nest when two or more were concurrently active on his territory. Female feeding rate decreased through the nesting season. Female feeding rate was independent of male feeding rate and female status, so nestlings fed by both parents received more food than those fed only by the female. As a result, fewer nestlings starved in pair-fed broods, and these broods produced more fledglings than female-fed broods. Thus, both males and females are affected by their experience, and appear to respond to 'nestling demand'. While male and female provisioning can be interpreted in terms of the costs and benefits of specific investment strategies, identification and quantification of the costs and benefits, and experimental studies to examine their effects are clearly needed for a more complete under-standing of parental investment in the red-winged blackbird. © 1990 The Association for the Study of Animal Behaviour.