The Role of Sibling Competition and Parental Provisioning on Food Distribution among Ferruginous Hawk Nestlings

Abstract

Parent-offspring conflicts arise through the competing efforts of the parents (to optimize their reproductive success) and the offspring (to secure maximum resources for themselves to enhance survival). Competition among siblings in a brood plays a key role in each nestling's relative fitness, particularly in avian species that hatch asynchronously. Previously published research has shown that the first-hatched nestling secures the most food, often at an energetic cost to its siblings. However, few researchers have simultaneously investigated competition and parental allocation behaviors to determine their effects on food distribution among raptor nestlings. We found that Ferruginous Hawk (Buteo regalis) parents delivered the same number of prey to nests, regardless of brood size. Contrary to our expectations, all nestlings consumed a similar amount of food within individual feeding events. Importantly, neither nestling competition nor parental allocation was the dominant process responsible for equal food distribution. Instead, the first-hatched and second-hatched nestling gained more food by competition, and the third-hatched nestling gained more food through parental allocation. Although each nestling attempted to optimize its food consumption relative to its siblings, resulting in unequal competitive outcomes, parents altered their allocation behavior to offset sibling competition. Ultimately parents provided the last-hatched nestling with more food, and thereby controlled food distribution to maximize their reproductive output. Future work should explore the role of nestling competition and parental allocation on food distribution using supplementation at nests when prey abundance in the environment is low.