Parental investment and brood value in tree swallows, Tachycineta bicolor

Abstract

Summary Parent birds are predicted to provide greater care to broods with greater value. Begging vocalizations may provide proximate cues of brood value. Finally, parental quality may also affect care. We assessed parental care in nestling tree swallows (Tachycineta bicolor) relative to brood value in both natural broods, and in those where brood size and flea loads (Ceratophyllus idius) were manipulated. We also quantified parental quality (based on their size and mass), nestling sex and age (natural broods only), and begging vocalizations (manipulated broods only). Feeding rates were not related to brood value in natural brood sizes (range 2‐6), but were positively related over the range (1‐8) of manipulated brood sizes. Defence intensity was greater for larger and heavier nestlings, independent of age, in natural broods, but not in manipulated broods. Although measures of parental investment were not significantly related to flea load, flea manipulations did not result in higher flea loads when measured following fledging. Parental feeding rates were not associated with variation in parental morphology, but defence intensity was higher by females with longer tails and by heavier males. In our population of tree swallows, only a few of the predicted relationships from parental investment theory were supported.