REGULATION OF PARENTAL EFFORT IN A LONG-LIVED SEABIRD - AN EXPERIMENTAL MANIPULATION OF THE COST OF REPRODUCTION IN THE ANTARCTIC PETREL, THALASSOICA-ANTARCTICA

The fitness of a parent in an altricial bird species is likely to be a function of the proportion of resources allocated to offspring produc tion in relation to the amount spent on its own survival. Here we repo rt an experiment on the Antarctic petrel in which we manipulated the c osts of rearing an offspring by placing small lead loads on the legs o f one parent. The bird could then either decrease its own body reserve s or reduce the food load to the chick. The manipulated birds decrease d their food load and increased the feeding interval, compared with un manipulated birds. Consequently, the rate of chick loss increased. No significant difference was found between the body weights of experimen tal and control birds during the experiment.