Survival throughout the annual cycle of first year Canada Jays in the context of sibling competition, expulsion, and adoption

Abstract

For most birds that exhibit delayed dispersal (remaining on the natal territory rather than dispersing to seek a breeding opportunity), siblings appear free to stay or leave the natal area. However, in rare cases, delaying dispersal is determined via conflict among siblings, with the dominant individual remaining on the natal territory. We used radio-tracking to examine brood reduction, and subsequent juvenile survival, of first-year Canada Jays (Perisoreus canadensis) in Algonquin Provincial Park, Ontario, Canada. Soon after juveniles become nutritionally independent, intra-brood struggles lead to one “dominant juvenile” remaining on the natal territory after permanently expelling the subordinate siblings (“ejectees”). Males in above-average condition when nestlings were the most likely to become the dominant juveniles and females did so only when broods were all-female at the time of the expulsion. dominant juveniles were much more likely to survive their first summer compared to ejectees (survival probabilities = 0.84 and 0.45, respectively), suggesting that ejectees are especially vulnerable to mortality risk in the critical interval between their expulsion from the natal territory and their settlement on a new territory. However, if ejectees lived to autumn, they had only a slightly lower probability of first-winter survival (0.73) than dominant juveniles (0.85). These results suggest that the survival advantage gained by dominant juveniles is greatest during the first summer after hatching, with a much smaller difference over the first winter after ejectees have settled on non-natal territories. Our work provides insight into potential evolutionary and ecological mechanisms driving social dominance hierarchies in wild birds.