Begging and Asymmetric Nestling Competition

Abstract

Genotypically, all offspring are created equal, but maternal manipulations of phenotype can render some offspring more equal than others (e.g. differences in egg size or composition, hormonal titre or hatching interval). A phenotypic handicap results when such variation impairs an individual’s competitive status. Here we examine both the causes and consequences of manipulations of such phenotypic handicaps. Hatching asynchrony is the primary handicap; differences in egg size and hormonal manipulations play secondary roles, unless offspring hatch synchronously. Begging strategies are role-dependent: last-hatched marginal offspring generally beg harder, but receive less food than earlier-hatched core offspring, consistent with phenotype-limited models of begging behaviour. There are alternative, though not mutually exclusive, explanations for such behaviour. Smaller nestlings may simply be hungrier, or influenced by different hormonal titres. Future work should focus on role-dependent begging strategies, such as whether marginal nestlings modulate their begging effort according to thei prospects of winning.