CONFIDENCE OF PATERNITY AND PATERNAL CARE BY EASTERN BLUEBIRDS

Male birds are often faced with low confidence of paternity in their m ates' offspring, raising the question of how paternal care covaries wi th confidence of paternity. We tested the hypothesis that male eastern bluebirds (Sialia sialis) reduce care of nestlings in response to exp erimentally decreased confidence of paternity. Actual paternity, as as sessed 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 wa s fertile (experimental group) fed nestlings at absolute rates similar to those of control males. The proportion of feeding trips provided b y males was also similar for control and experimental nests. We found no difference in fledging success and nestling growth between experime ntal and control broods. Seven original resident males were displaced by previously unbanded males. Although these replacement males appeare d to feed nestlings at normal rates, the nests attended by replacement males suffered reduced fledging success compared to control and exper imental nests. Overall, we found no evidence that males reduce feeding effort when confidence of paternity is experimentally decreased. Male s may tolerate some reduction in confidence of paternity without reduc ing care if paternal care is crucial to nestling survival. Alternative ly, males may assess paternity within a brood using cues other than th eir ability to guard their fertile mates.