Eyes on the future: buffering increased costs of incubation by abandoning offspring

Life history theory states that the resources invested in current reproduction must be traded off against resources needed for survival and future reproduction. Long-lived organisms have a higher residual reproductive value and are therefore expected to be sensitive to reproductive investments that may reduce survival and future reproduction. Individuals within a population may vary in phenotypic quality, experience, access to resources etc. This may affect their optimal reproductive investment level. In this study we manipulated reproductive costs by shortening and extending the incubation period in common eiders Somateria mollissima without altering clutch size. Females whose incubation time was prolonged experimentally, suffered higher mass loss and increased clutch loss/nest desertion. These females were also more prone to abandon their brood after hatching. Both clutch loss and brood abandonment decreased with clutch size in all treatment categories, indicating higher phenotypic quality and/or better access to resources for females producing more eggs. However, although females with prolonged incubation were lighter at hatching, their return rate and breeding performance in the following year were unaffected. These results show that individual quality as expressed through clutch size and body mass is affecting current reproductive investment level as well as future survival and breeding performance. The results also show that individual birds are sensitive to changes in their own condition, and when reproductive effort is approaching a level where survival or future survival may be compromised, they respond by terminating their current reproductive attempt.