Parental nepotism enhances survival of retained offspring in the Siberian jay

The evolutionary payoff accruing to parents from breeding offspring could b e an incentive for prolonged investments in the offspring. Enhanced surviva l for offspring as a result of such a prolonged parental investment would i ncrease the value of remaining in the natal territory for the offspring. He re we shaw that first-year survival in Siberian jays is higher in the compa ny of their parents. Two observations point to that the enhanced survival o f retained offspring is due to nepotistic parents rather than to the qualit y of a shared habitat. First, winter survival is higher only for those reta ined offspring whose parents have survived too; this precludes the possibil ity 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 possi bility of a correlation between the survival of parental birds and unrelate d immigrants to the territory. Such a correlation would have been expected if survival reflected habitat quality and not kinship. Our data instead sug gest a direct fitness gain to retained offspring in enhanced survival throu gh parental nepotism (parental facilitation). The behavior of parents in al lowing retained offspring access to food that is denied to immigrants is on e proximate mechanism mediating a benefit of delayed dispersal.