Certain aspects of the breeding biology of the kittiwake (Rissa tridactyla)
Data on aspects of the breeding biology of a colony of Kittiwakes in North East England, in which all breeding adults are individually colour-marked, have been collected annually since 1954. The inter-relationships between different factors have been investigated and year-to-year changes in the breeding biology of the colony, related to changes in population structure. Date of return to the colony is shown to be primarily determined by age. Synchrony of return between the members of a breeding pair is associated with the maintenance of the pair bond. Other factors influencing the duration of the pair bond are investigated, including the prior association between the members of the pair, breeding success in the previous year and mortality rates in different years. As birds get older, the main cause of the break-up of the pair bond changes from 'divorce' to bereavement. Time of breeding is related to the location of the nest site (centre or edge of the colony) and the breeding experience of the two members of the pair. There is a tendency for breeding to become more synchronised amongst older age groups, with females laying progressively closer to the mean date of laying for the colony as a whole. The possible interactions between environmental cues, stimulus from the mate and stimulus from the rest of the colony are discussed. Clutch size is shown to be independently influenced by breeding experience, date of laying, location of the nest site and the status of the pair (retention of the same mate as in the previous year, or change). Variations in the size and shape of eggs laid by different females are investigated with respect to many of the above factors.