ENVIRONMENTAL CONDITIONS AND BREEDING EXPERIENCE AFFECT COSTS OF REPRODUCTION IN BLUE PETRELS

Abstract

Using data from a 17-year study of individually marked Blue Petrels, we examined how survival and breeding probability varied with experience and breeding status, and looked for costs of first reproduction, taking into account environmental and individual variability. Using multistate capture–recapture models with four states (inexperienced nonbreeders, first-time breeders, experienced breeders, and experienced nonbreeders), we found that first-time breeders had a lower probability of surviving and breeding in the next year than experienced breeders. Survival of first-time breeders was lower than that of inexperienced nonbreeders, indicating a cost of first reproduction. Survival of inexperienced individuals (both breeders and nonbreeders), but not of experienced ones, was negatively affected by poor environmental oceanographic conditions. The costs of reproduction for first-time breeders were particularly marked during harsh weather conditions. Survival and the probability of breeding in the next year for experienced birds were higher for breeders than for nonbreeders. Similarly, the probability of breeding in the next year for first-time breeders was higher than for inexperienced nonbreeders. This suggests heterogeneity in quality among individuals. Experienced breeders had a higher body condition than first-time breeders and nonbreeders. Body condition did not affect the probability of surviving or breeding in the next year. These results can be interpreted in the light of a change in the proportion of individuals with different survival (selection hypothesis: low-quality individuals die sooner). The inferiority of first-time breeders may be linked to a higher proportion of lower-quality individuals in younger age classes. First reproduction may act as a filter, selecting individuals of higher quality. Sea surface height, reflecting food availability, is probably a key selective agent.