The effect of maternal age and experience on egg-size and hatching success in Wandering Albatrosses Diomedea exulans
The roles of maternal age and experience, on the one hand, and individual, year and random effects on the other, in influencing avian egg-size and hatching success have been much debated but seldom studied comprehensively. We investigated these topics with Wandering Albatrosses Diomedea exulans of known age (7–30 years) and experience (1–8 breeding attempts) over a 10-year period. Older and more experienced birds laid larger eggs. After allowing for year and controlling for experience, significant age effects remained; after controlling for age, no detectable experience effects remained. However, age accounted for only 6% of the overall egg-size variation. Egg-size varied significantly between years and has increased over the last decade. Individuals laid eggs of consistent sizes; 55% of the random variation in egg-weight was due to such effects. Egg- and hatchling-weight were very closely linked; larger eggs also had higher hatching success. The latter was influenced significantly by age and experience but neither remained significant after controlling for the other. Year effects were also detectable.
That there are significant effects of age, experience, year and individual on egg-weight (and hatching success) is probably typical of seabirds generally, though with different balances between factors depending on species and situation; however, insufficient data exist to examine this critically. Our finding that age was a more important influence than breeding experience does not support recent suggestions that hatching success is mainly influenced by experience and that experience will have a greater effect on reproductive success in long-lived species with high mate-fidelity. However, Wandering Albatrosses may have acquired much relevant experience before even starting to breed.