Mechanistic regulation of begging behavior due to experimental food supplementation across an urbanization gradient

Parent-offspring communication is fundamental to reproductive success, yet how ecological variation shapes nestling begging behavior, physiology, and parental provisioning remain understudied in free-living systems. We investigated these relationships in free-living northern house wrens (Troglodytes aedon) breeding across an urbanization gradient differing in food availability. Within each population, we experimentally supplemented half of the nests with mealworms while the remaining nests served as non-supplemented controls to determine whether food availability alters offspring begging behavior, parental provisioning, and baseline corticosterone concentrations. Parent-offspring communication changed markedly with nestling age. At 5-6 days, begging intensity primarily reflected the interaction between parental provisioning and seasonal timing, whereas by 11 days it reflected local food availability and nestling body mass. This developmental shift was accompanied by changes in parental provisioning: as nestlings aged, parents relied increasingly on offspring behavior when allocating food. Nestlings with higher begging scores were more likely to receive food, but successful food acquisition depended primarily on the timing of begging relative to parental feeding decisions rather than on begging duration alone. Food supplementation weakened population differences in parent-offspring communication, indicating that variation in food availability underlies much of the observed behavioral variation. Baseline corticosterone concentrations decreased with increasing food intake only in the population with the lowest food availability. Furthermore, larger nestlings exhibited higher baseline corticosterone concentrations under conditions of high begging intensity and low parental provisioning. In contrast, natural variation in baseline corticosterone did not predict begging behavior, suggesting that baseline corticosterone reflects the energetic and ecological context in which begging occurs rather than acting as its direct driver. Our findings demonstrate that parent-offspring communication is highly context dependent and changes substantially during development, highlighting the importance of considering both offspring behavior and ecological context when studying the evolution of parent-offspring interactions.