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Parents of many species provide multiple forms of care to their offspring. In many birds, parents often provision offspring with food and defend them from predators and/or nest-site competitors. We tested how these two forms of parental care covary in a wild population of house sparrows (Passer domesticus). Using a behavioral reaction norm approach, we found that nestling provisioning exhibited between individual differences and positively covaried with a measure of nest defense: the propensity to attack a heterospecific nest box competitor, the European starling (Sturnis vulgaris). This result would seem to support parental investment theory and suggests that high-provisioning parents have high-value offspring, which they will defend more vigorously than low-provisioning parents. In addition, we found that parents with nestlings that hatched earlier in the season and grew faster approached a model starling more frequently and tended to be more likely to strike the starling. However, we also found that although brood value explained significant variation in both nestling provisioning and nest defense, it did not eliminate the positive, between-individual relationship between provisioning and defense. This suggests that some of the correlation between provisioning and defense is tied to individual identity and hence may be a behavioral syndrome in which differences between individuals in underlying attributes produce correlated behaviors. |
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