Survival of Gannets Morus bassanus in Britain and Ireland, 1959-2002

Aims To obtain the first estimates of the survival of British and Irish Gannets from ringing recoveries. Methods Ringing and recovery data were analysed to obtain estimates of survival probabilities, using a range of statistical models for such data and the software MARK. Results The mean annual survival for adults was 0.919 with little difference between birds ringed as chicks on the Bass Rock (0.916) and those ringed at other colonies (0.922). Annual survival over the first four years of life increased gradually from 0.424 to 0.895 before reaching this adult value. Prior to maturity there were differences between the survival probabilities of chicks ringed on the Bass Rock and those ringed elsewhere, but for both groups survival to age four years was about 0.30. A recent lower rate of increase of the population could well be due to a decline in adult survival rates during the 1990s. Conclusion The estimated survival probabilities imply annual population growth that agrees well with the measured rate of population increase for the British and Irish breeding population up to the mid-1990s. However, for recoveries to keep track of up-to-date changes in the survival of Gannets during the current period, when the rate of population increase is slowing down, then either the rate of recovery or the numbers of adults ringed must be increased