Breeding Behavior, Nestling Growth, and Begging Behavior in the Plain Laughingthrush (Garrulax davidi): Implications for Parent-Offspring Conflict

Investigation on food allocation among nestlings of altricial birds is crucial in understanding parent-offspring conflicts within avian families. However, there is no consensus in empirical studies regarding whether parents or offspring determine the food allocation pattern within a brood. In the Plain Laughingthrush (Garrulax davidi), we examine the relationship between parental feeding strategies and nestling begging behaviors. Due to hatching asynchrony, larger nestlings have a competitive advantage in food acquisition over their smaller brood-mates; nevertheless, if the initial food-receivers were already satiated and did not immediately consume the food, parents would retrieve the food and re-allocate it to another nestling. This re-feeding tactic employed by parents reduced the likelihood of early-hatched nestlings monopolizing the food solely due to their larger body size. Our findings indicate that parents primarily allocated food based on nestling begging intensity, while their re-feeding tactic is determined by whether the first food-receivers have consumed the food. To date, our research demonstrates that while parental food allocation primarily hinges on the begging intensity of the nestlings, the decision to re-feed is contingent upon whether the initial recipients of the food ingest it immediately.

Adult Provisioning Influences Nestling Corticosterone Levels in Florida Scrub Jays (Aphelocoma coerulescens)

We studied Florida scrub jay (Aphelocoma coerulescens) nestlings to examine the relationship between parental feeding rates and levels of corticosterone (CORT), a metabolic and stress-related steroid hormone hypothesized to play a role in mediating begging behavior. It has been documented that nutritional deficiency results in increased glucocorticoid levels in nestling birds. Further, previous studies have found that CORT levels of Florida scrub jay nestlings are negatively correlated with parental nest attendance and provisioning rates; however, the behavioral observations were made several days before the collection of samples to assess CORT levels. Few studies have investigated whether experience immediately before sampling impacts nestling glucocorticoid levels, especially in a free-living species. By monitoring parental activity at the nest before sample collection, we found that nestling CORT levels varied as a function of parental provisioning rate and the time since their last feed. However, counter to our predictions, higher provisioning rates and more recent feedings were associated with higher CORT levels in nestlings rather than lower CORT levels. These results suggest that some aspect of parental provisioning results in increased CORT levels in nestling Florida scrub jays.