Confidence of paternity and paternal care by eastern bluebirds

Male birds are often faced with low confidence of paternity in their mates' offspring, raising the question of how paternal care covaries with confidence of paternity. We tested the hypothesis that male eastern bluebirds (Sialia sialis) reduce care of nestlings in response to experimentally decreased confidence of paternity. Actual paternity, as assessed by DNA fingerprinting, had no effect on male feeding rates, nor did males reduce care when confidence of paternity was experimentally decreased. Males that had been removed for 2 days while their mate was fertile (experimental group) fed nestlings at absolute rates similar to those of control males. The proportion of feeding trips provided by males was also similar for control and experimental nests. We found no difference in fledging success and nestling growth between experimental and control broods. Seven original resident males were displaced by previously unbanded males. Although these replacement males appeared to feed nestlings at normal rates, the nests attended by replacement males suffered reduced fledging success compared to control and experimental nests. Overall, we found no evidence that males reduce feeding effort when confidence of paternity is experimentally decreased. Males may tolerate some reduction in confidence of paternity without reducing care if paternal care is crucial to nestling survival. Alternatively, males may assess paternity within a brood using cues other than their ability to guard their fertile mates.