Food allocation in crimson rosella broods: parents differ in their responses to chick hunger

Abstract

Food allocation in many asynchronously hatching bird species favours large, competitively superior chicks. In contrast, food is usually distributed equally within broods of crimson rosellas, Platycercus elegans, implying that parents do not simply feed the most competitive chick. We used two temporary removal experiments to manipulate hunger of: (1) individual first- or last-hatched chicks, or (2) the whole brood. When only a single chick was hungry, parents compensated fully and chicks gained the same mass over the day as during controls. Mothers and fathers, however, responded in different ways to chick hunger. Mothers did not strongly alter their food allocation when a single chick was hungry, and controlled the distribution of food by refusing to feed first-hatched chicks when they were hungry and by moving more during feeds. In contrast, fathers allocated more food to hungry last-hatched chicks. When the whole brood was hungry, parents were unable to compensate chicks and all chicks lost mass over the day. In these conditions, mothers preferentially fed first-hatched chicks, while fathers fed all chicks equally. Our results show that both mothers and fathers were able to discriminate and selectively feed chicks, but that parents responded differently to changes in chick hunger within the brood. Fathers responded more strongly to variation in chick hunger within the brood, suggesting they reallocate food based on short-term changes in hunger. Mothers distributed food preferentially to last-hatched chicks except when the whole brood was hungry, when they switched to favouring first-hatched chicks. This pattern is consistent with a strategy of adaptive brood reduction when food is scarce.