THE RELATIONSHIP OF PAIR-BOND FORMATION AND DURATION TO REPRODUCTIVE SUCCESS IN SHORT-TAILED SHEARWATERS PUFFINUS-TENUIROSTRIS

1. A substantial correlation exists between the breeding ages of short-tailed shear-waters in pair-bonds. 2. Much of this correlation can be explained by prolonged pair-bonds between the same mates, and the predominant availability of unpaired, inexperienced birds. 3. Using Monte Carlo simulation, a comparison of the differences in age observed between pair members with those produced assuming random pairing of available birds, indicated some weak assortative mating on the basis of breeding age. 4. The probability of breeding success depended both upon the breeding ages of the partners and upon the length of time they had bred together; the latter appeared the stronger effect. 5. In the first year of a pair-bond, the breeding age of the female had a much stronger effect than that of the male in determining the probability of reproductive success.