REGULATION OF PARENTAL INVESTMENT IN THE ANTARCTIC PETREL THALASSOICA-ANTARCTICA - AN EXCHANGE EXPERIMENT

An experiment was conducted on the Antarctic petrel to test whether th e parents were able to respond to changes in food demand of their offs pring. Two experimental groups were formed by replacing eight 20-day-o ld chicks with 10-day-old chicks, and vice versa. The growth rate of c hicks in the experimental groups was compared with that in two control groups with chicks of known age. The growth rate of 10-day-old chicks in the nests of parents which initially had 20-day-old chicks did not differ significantly from that in their respective control groups. Th is indicates that those parents were able to raise a new young nestlin g, despite having already raised another chick from hatching to 20 day s. However, the 20-day-old chicks placed in nests with 10-day-old chic ks had a significantly lower growth rate than their control group. Fee ding rate per day and nest did not differ significantly among any of t he groups. This suggests that the observed difference in growth rate b etween 20-day-old chicks is related to a lower amount of food delivere d per visit to experimental chicks. Thus, in the Antarctic petrel, the feeding rate apparently is not regulated by the status of the chick, but by the parents' ability to gather food or willingness to provide f ood for the chicks.