THE INFLUENCE OF MATE RETENTION AND DIVORCE UPON REPRODUCTIVE SUCCESS IN SHORT-TAILED SHEARWATERS PUFFINUS-TENUIROSTRIS

Half of all male and female short-tailed shearwaters had only one breeding partner during their lives; the maximum was 7 mates. Pair bonds lasted longer later in life. Half of all first-pair-bonds, but only 1/3 of all 3rd pair-bonds, lasted 1 yr. The percentage of pairs laying eggs and the percentage of those eggs which resulted in free-living young rose markedly with increasing duration of a pair-bond, except in later pair-bonds. Breeding success on the 1st attempt with a new partner was greater in later pair-bonds. Breeding success on the 1st attempt with a new partner was greater in later pair-bonds. Thus, increasing total breeding experience and increasing familiarity with a particular partner are both related to increasing reproductive performance. Birds whose pair-bonds lasted >3 yr had a greater reproductive success than those in shorter pair-bonds, not only due to increasing breeding experience and mate familiarity, but also initially. This differential persisted throughout the 1st 2 pair-bonds, but not thereafter. In both sexes, 74% retained their mate of the previous year, 10% took a new mate after their previous mate died and 16% divorced their living mate. Divorce was more likely if a pair failed to produce young in the preceding season; impending divorcees were also absent during a pair-bond more often than birds retaining their mates. -Authors