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

Recent theoretical models of parent-offspring conflict suggest that co stly solicitation by offspring reflects offspring need in a reliable m anner, and that parents are, therefore, selected to increase parental effort in response to offspring solicitation. However, theory and expe riments suggest that parents pay attention not only to their nestlings ' needs, but also to their relative quality as reflected by size and c ompetitive ability. A study on barn swallow nestlings, described here, investigates how such complex feeding rules affect nestling begging s trategies, 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, re spectively. The results indicate that small nestlings tend to beg at g reater intensities than large nestlings for a similar level of food de privation. A-higher intensity of begging does not, however, guarantee greater success for smaller nestlings because mass gain by nestlings i s affected by both size and begging differences among the competing ne stlings. I suggest that higher levels of begging by small nestlings ar e caused by differences in the expected benefit for a given level of b egging, 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 be tween the optimal level of signaling and the signaler's quality. This study suggests that ''negatively correlated handicaps'' may emerge whe never receivers integrate cryptic information about the signaler's mom entary need or motivation, based on one signal, and non-cryptic inform ation about the signaler's quality based on other cues.