The cost of egg production: increased egg production reduces future fitness in gulls

Measurements of costs of reproduction are essential for our understanding o f the evolution of reproductive effort. While in birds the effects of incre ased chick-rearing effort on subsequent survival and fecundity have been re latively well studied experimentally. costs associated with increased egg-p roduction effort have received relatively little attention. We experimental ly increased the egg-production effort of individually marked Lesser Black- hacked Gulls Larus fuscus and followed their breeding performance in the ne xt year. In the season following increased egg production. females, but not males. were less likely to he resighted in the study plot and those that d id return were less likely to prod;ce a clutch compared to control birds. I t is unclear whether the observed effect on local return rate represents di fferential survival. differences in breeding propensity or differences in d ispersal between experimental and control females, in any event, all of the se would adversely affect the fitness of experimental females. In addition, those experimental females that did breed invested less in egg production the following season. which again is likely to affect breeding performance. Thus. this study provides evidence that there is an inter-brood trade-off between current egg-production effort and future fitness in birds.