UC San Diego

We studied the nestling begging behaviors and parental provisioning responses of the phainopepla (Phainopepla nitens), a sexually dichromatic silky flycatcher native to Mexico and the southwestern United States deserts. Because of its small clutch size (usually two eggs) and synchronous hatching strategy, we predicted that size- based nestling competitive interactions and brood reduction strategies would be absent, so that parental food allocation would accurately reflect nestling need. At eight nests we temporarily removed one nestling to deprive it of food, and video-taped the nestling and adult behaviors after the nestling was returned to the nest. Both male and female parents preferentially allocated food to the hungry nestling, but used different provisioning strategies and nestling cues to achieve this result. Males increased their visit rate and food load and used begging start order and initial beak height, as well as beg duration and intensity, as cues to allocate food. By contrast, females only increased food load and allocated resources to the nestling that begged more intensely. Most of our study nests were attended by only one parent. Hungry nestlings in male and female nests used different begging strategies associated with the cues employed by the parent (start/height in male nests, beg intensity in female nests). Nestlings appear to learn which begging signal components are most likely to generate food rewards. We suggest that conditioned learning could be a common mechanism by which nestlings adjust their begging behavior to their need, but would lead to an honest parent -offspring signaling system only when conflicts of interest between sender and receiver are absent and competing senders experience similar conditioning regimes