The long-term consequences of egg predation

Disrupted breeding, caused by predation of eggs or young, may have long-term fitness consequences as costs related to initiating a new breeding attempt may reduce future reproduction and survival (the "cost of reproduction" hypothesis). Alternatively, these apparent costs may stem from animals avoiding breeding in areas where they have experienced previous predation (the "predator avoidance" hypothesis). We studied effects of nest predation in female common eiders Somateria mollissima by removing all eggs from newly initiated clutches; renesting attempts and future breeding of these females were thereafter registered and compared with controls where eggs were not removed. These groups were also compared with depredated birds not renesting to explore the possibility that apparent costs of renesting may in fact be predator avoidance. Fifty percent of the experimentally depredated females started a replacement clutch, always at a new nest site within the colony. In both the experimentally and naturally depredated groups, both the females that renested and the females not renesting showed a reduced recapture rate and lower number of future breeding attempts when compared with control females that successfully hatched their clutch, while apparent survival was not significantly affected by their reproductive allocation. Thus, losing offspring during a breeding attempt seems to lead to adaptive avoidance of the breeding site, which in turn may reduce future fitness if alternative breeding sites are not available.