Red-winged blackbird females fail to increase feeding in response to begging call playbacks

The begging behaviour of nestling birds appears to be the main signal telling parents how much food is needed by the brood. Not only may the accuracy of that information be reduced through exaggeration due to competition, but it may also vary with the age of the nestling. Younger nestlings map vary more in how frequently they call than older nestlings because they cannot discriminate stimuli as well. Thus even if 'honest', begging from younger nestlings could be a less reliable hunger signal. than;that from older nestlings. We tested the prediction that parents should respond less to the increased frequency of begging from very young versus older nestlings by playing back begging calls at the nests of both younger (less than or equal to 5 day) and older (greater than or equal to 6 days) red-winged blackbirds, Agelaius phoeniceus. In neither case did parents respond with consistent increases in feeding, nor did young gain more weight during playbacks. This lack of response is discussed in relation to two other recent studies of blackbirds that did demonstrate increased feeding with playbacks of begging; calls. (C) 1998 The Association for the Study of Animal Behaviour.