HIGHER LEVELS OF BEGGING BEHAVIOR BY SMALL NESTLINGS: A CASE OF A NEGATIVELY CORRELATED HANDICAP

ABSTRACT

Recent theoretical models of parent-offspring conflict suggest that costly solicitation by offspring reflects offspring need in a reliable manner, and that parents are, therefore, selected to increase parental effort in response to offspring solicitation. However, theory and experiments suggest that parents pay attention not only to their nestlings' needs, but also to their relative quality as reflected by size and competitive ability. A study on barn swallow nestlings, described here, investigates how such complex feeding rules affect nestling begging strategies, and how different begging strategies affect the nestlings' relative success. Begging strategies were compared for large and small brood mates, assumed to represent high and low nestling qualities, respectively. The results indicate that small nestlings tend to beg at greater intensities than large nestlings for a similar level of food deprivation. A higher intensity of begging does not, however, guarantee greater success for smaller nestlings because mass gain by nestlings is affected by both size and begging differences among the competing nestlings. I suggest that higher levels of begging by small nestlings are caused by differences in the expected benefit for a given level of begging, and create a negative correlation between the optimal level of signaling and the signaler's quality. This contrasts with the typical handicap case discussed in the literature, in which differences among individuals in the cost of signaling create a positive correlation between the optimal level of signaling and the signaler's quality. This study suggests that “negatively correlated handicaps” may emerge whenever receivers integrate cryptic information about the signaler's momentary need or motivation, based on one signal, and non-cryptic information about the signaler's quality based on other cues.