AN EXPERIMENTAL-STUDY OF REDUCED PARENTAL EFFORT AND FUTURE REPRODUCTIVE SUCCESS IN THE PUFFIN, FRATERCULA-ARCTICA

1. The puffin, a long-lived seabird, was studied on the Isle of May, E ast Scotland between 1990 and 1992. During two of these years, parenta l effort was experimentally decreased by supplementary feeding of youn g. This aimed to identify inter-year reproductive costs, and show whet her they took the form of reduced adult survival, reduced hedging succ ess and/or a reduction in the 'quality' of offspring in the following year. 2. The feeding treatment significantly reduced the daily number of feeds delivered by experimental parents by 67% in 1990 and 87% in 1 991. 3. The proportions of experimental and control parents returning to the colony in the year following manipulation did not differ signif icantly, although in 1991, 2.5 times as many controls (young unfed) as experimental birds (young fed) failed to return. 4. The fledging succ ess of experimental pairs in the year following manipulation (68%) was significantly higher than that of controls (24%). 5. Experimental pai rs raised young with significantly higher body condition (Residual Pea k Mass) than that of controls in the year following manipulation (1992 ). 6. Experimental parents did not differ from controls in their body condition (Lipid Reserve Mass) or rate of reserve depletion, either in the year of manipulation or in the following breeding season; hence t here was no evidence for a role of the measured component of body cond ition in the cost mechanism. 7. The study demonstrated inter-year repr oductive costs for puffins and supported the hypothesis that long-live d species reduce the 'quality' of their offspring or abandon a breedin g attempt rather than compromise their survival and future opportuniti es to reproduce.