Parental nepotism enhances survival of retained offspring in the Siberian jay

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Abstract
The evolutionary payoff accruing to parents from breeding offspring could be an incentive for prolonged investments in the offspring. Enhanced survival for offspring as a result of such a prolonged parental investment would increase the value of remaining in the natal territory for the offspring. Here we show that first-year survival in Siberian jays is higher in the company of their parents. Two observations point to that the enhanced survival of retained offspring is due to nepotistic parents rather than to the quality of a shared habitat. First, winter survival is higher only for those retained offspring whose parents have survived too ; this precludes the possibility that the link between timing of dispersal and survival should reflect a higher phenotypic quality of retained offspring in general. Second, there is no support for the more parsimonious explanation that this link between the survival of parents and retained offspring reflects habitat quality of a shared territory. We could, with high statistical power, reject the possibility of a correlation between the survival of parental birds and unrelated immigrants to the territory. Such a correlation would have been expected if survival reflected habitat quality and not kinship. Our data instead suggest a direct fitness gain to retained offspring in enhanced survival through parental nepotism (parental facilitation). The behavior of parents in allowing retained offspring access to food that is denied to immigrants is one proximate mechanism mediating a benefit of delayed dispersal.

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