Causes and consequences of individual variation in the cooperative breeding behaviour of the endangered El Oro Parakeet (Pyrrhura orcesi)

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The costs of cooperation pose a fundamental puzzle to understand the evolution of cooperation. The prevailing view is that direct and indirect benefits arising from cooperation among relatives offset the costs of cooperation. While this paradigm has overall been supported, it cannot easily account for the pronounced individual differences in many cooperative systems that occur even under seemingly identical conditions. Studying the fitness consequences of individual variation in cooperative breeding provides a functional understanding of cooperation because of the immediate link to reproduction and fitness. Although cooperative breeding is not rare, it is controversial whether helpers actually increase the fitness of breeders or whether they primarily benefit from group living when their own reproduction is constrained. Here, we investigate various hypotheses on the causes and consequences of individual variation in cooperative breeding behaviour in the endangered El Oro Parakeet (Pyrrhura orcesi). We determine individual consistency in cooperative behaviour within and among years and in different social environments. These data reveal whether individual contribution to brood care is variable and primarily state dependent or whether it is invariant and best seen as a personality trait. Combining behavioural with genetic analyses allows us to disentangle in cross-fostering experiments whether cooperation is shaped by cultural or genetics effects. Based on a long-term dataset we study the consequences individual variation in cooperative behaviour. In particular, we study whether very cooperative helpers raise more related offspring or whether they attain breeding position more quickly. This will reveal whether cooperative breeding is mutualistic yielding fitness benefits to breeders and helpers or whether it provides fitness benefits only to breeders through coercion or only to helpers through group living.