Individual Variation in Behavior and Breeding Success of Northern Fulmars

Abstract

-In a sample of breeding Northern Fulmars (Fulmarus glacialis) observed in 45 years, up to 43% of the variability in 13 attributes of breeding behavior was consistent among individuals or pairs. Sample means for most attributes were correlated in a predictable way with annual levels of breeding success. Except for laying dates, there was little evidence that individual differences in these attributes contributed to variation in breeding success. A test of breeding experience as a contributing factor revealed an interaction between individual and annual components of variation. During years when the whole population did relatively poorly, pairs with no previous breeding experience were affected disproportionately. Late-nesting fulmars were more successful than early layers, possibly because delayed breeding ensured that food availability was adequate for successful incubation. Received 7 November 1989, accepted 15 May 1990. IF the same sample of breeding birds is monitored in several years, the observed variance in breeding success has annual and individual components. Annual variation arises from variability in environmental factors such as food supply, predation, disease, weather, or disturbance. Any added component of individual variation arises from differences in the quality of the habitats occupied by individuals (Nettleship 1972, Birkhead 1977, Hudson 1982), or from differences in the quality of the individuals themselves (Coulson 1968, Potts 1969, Reilly and Cullen 1981). Interaction between the two components of variation is expected because annual changes in the environment need not affect all individuals equally. In a 6-yr study of breeding Northern Fulmars (Fulmarus glacialis), I found that young were more likely to be raised successfully in some sites than others (Hatch 1988). Fulmars are longlived and have a strong fidelity to the same mate and nest site between years (Hatch 1987, 01lason and Dunnet 1988). Many of the birds in my sample were individually known from plumage differences, and all direct evidence indicated that few undetected changes of site ownership or pair bonds occurred during the study. I therefore hypothesized that the amongpairs component of variance in breeding success could be explained by individual differences in I Present address. breeding biology and behavior. Consequently, I assessed individual variation in laying dates and time allocation as factors that affect breeding success. I also considered the influence of breeding experience under the varying conditions that occurred during the years of study.