Confidence of paternity and paternal care by eastern bluebirds

Male birds are often faced with low confidence of paternityin their mates' offspring, raising the question of how paternalcare covaries with confidence of paternity. We tested the hypothesisthat male eastern bluebirds (Sialia sialis) reduce care of nestlingsin response to experimentally decreased confidence of paternity.Actual paternity, as assessed by DNA fingerprinting, had noeffect on male feeding rates, nor did males reduce care whenconfidence of paternity was experimentally decreased. Malesthat had been removed for 2 days while their mate was fertile(experimental group) fed nestlings at absolute rates similarto those of control males. The proportion of feeding trips providedby males was also similar for control and experimental nests.We found no difference in fledging success and nestling growthbetween experimental and control broods. Seven original residentmales were displaced by previously unbanded males. Althoughthese replacement males appeared to feed nestlings at normalrates, the nests attended by replacement males suffered reducedfledging success compared to control and experimental nests.Overall, we found no evidence that males reduce feeding effortwhen confidence of paternity is experimentally decreased. Malesmay tolerate some reduction in confidence of paternity withoutreducing care if paternal care is crucial to nestling survival.Alternatively, males may assess paternity within a brood usingcues other than their ability to guard their fertile mates.