ADJUSTMENT OF PARENTAL EFFORT IN THE PUFFIN - THE ROLES OF ADULT BODYCONDITION AND CHICK SIZE

We examined the adjustment of parental effort of puffins by switching 20-day-old chicks randomly between parents of known body condition. Am ong unmanipulated birds mass gain (5-20 days) and mass of 20-day-old c hicks was positively correlated with the body condition of parents at day 6. During the first 5 days after chick switching 28% (n = 55) of t he parents deserted their foster chick. Parents which deserted their f oster chick originally had a chick of their own that was smaller than that of those which did not desert their foster chick. Whether parents deserted their foster chick was also negatively related to the size o f the foster chick. The mass of the foster chick was more important th an the size of the parents' own chick in determining the desertion rat e of chicks. The mass gain of the foster chick during the first 5 days after switching was positively related to the body condition of foste r parents and also positively related to the mass of the foster parent s' own chick, but negatively related to the size of the foster chick. The results suggest that puffins adjust their parental effort accordin g to both their own body condition and the size of the chick. The latt er may indicate the chick's prospect of survival and recruitment to th e population.