REGULATION OF PARENTAL INVESTMENT IN A LONG-LIVED SEABIRD, THE PUFFIN FRATERCULA-ARCTICA - AN EXPERIMENT

We manipulated the investment needed by puffins to successfully raise a chick by experimentally reducing or prolonging the nestling period. The nestling period in one group was prolonged by replacing their 20-d old chick with a 6-d old foster chick. It was reduced in a second group by reversing the process. A third group was not manipulated and used as a control. When small chicks were replaced by large chicks, the growth rate of the new chicks did not differ from control chicks of similar age. When large chicks were replaced by small chicks the new chicks grew normally until the normal fledging time of controls. However, a significantly higher proportion of the chicks in the prolonged group was deserted by the parents. The few parents in the prolonged group that extended their nestling period were in poorer body condition at the end of the nestling period than were controls and parents with a reduced nestling period. The results show that, within the normal nestling period, the parents quickly adapted their feeding effort to the chick's needs, but that the amount of parental effort was regulated by the length of the period since hatching. The few parents that extended the nestling period did so at the expense of their own body condition.