Age, Experience and Other Factors Affecting the Breeding Success of the Fulmar, Fulmarus glacialis, in Orkney

Abstract

(1) In twenty-seven fulmars breeding for the first time, breeding success tends to be higher in those that are at least as old as the mean age at first breeding (9 2 years, S.E.0 39), due to improved fledging success. (2) Breeding success shows a significant positive correlation with age in fulmars with not more than three years breeding experience. (3) Breeding success shows a significant positive correlation with length of breeding experience in birds from 6 to I I years old, but not from 12 to 19 years old. (4) Breeding success shows a significantly different relation to breeding experience of the male than to that of the female. Males show a significant positive correlation between breeding success and breeding experience from their second to twenty-first breeding year; females show a significant positive correlation from their second to seventeenth breeding year, with a tendency for success to decline thereafter. (5) Significantly more males than expected pair with females with less breeding experience than themselves. (6) Breeding success shows a significant positive correlation with duration of pairbond, if it assumed that the pair-bond persists during years in which one member of the pair was not identified. (7) The mate and site of the previous year are retained in about 90% of cases. Changes tend to result in lower breeding success, especially in females. (8) There are indications from new pairs with at least one experienced bird that the male may influence the choice of nest site more than the female, and this results in better breeding success. (9) Change of mate occurs at 500 per annum, mostly due to disappearance of the mate. When divorce is followed immediately by re-pairing, breeding success before the divorce tends to be poorer than that of the newly formed pair. (10) Change of site occurs at 6-7% per annum. Pairs which change their site tend to have higher breeding success at the new site than they did at the old one. (11) There are indications that capture, especially of birds recorded breeding for the first time, reduces their success in the year of capture, and reduces the proportion of these birds seen breeding in the following year. (12) Breeding success shows a significant negative correlation with laying date. Established pairs laying after the median laying date are significantly more successful than new pairs which do so, but there is no significant difference before this date. (13) Laying date does not correlate significantly with breeding experience though the