The population ecology of red-billed gulls (Larus novaehollandiae scopulinus) of known age.

The Red-billed Gull Larus novaehollandiae scopulinus is endemic to New Zealand and is one of the commonest gulls on the coast. There have been no detailed studies of this gull other than some work on food (Gurr, 1947), breeding distribution (Gurr & Kinsky, 1965; Mills, 1969), and general accounts in Stead (1932) and Oliver (1955). There is, however, knowledge of the seasonal dispersal (Carrick, Wheeler & Murray, 1957), population regulation (Carrick & Murray, 1964), general breeding biology (Wheeler & Watson, 1963), and seasonal mortality (v. Tets, 1968) of the closely related Silver Gull L. n. novaehollandiae in south-eastern Australia. The present study has been confined to the population of gulls hatched or breeding at the Kaikoura Peninsula. This population is particularly suitable for research since annual banding of nestlings from 1958-59 has resulted in birds of known age forming a large proportion of' the population. This banded population has provided not only the opportunity to study the influence of age on the breeding biology, but also the chance to follow the progress of individual known-aged birds. This has allowed aspects such as mortality and pair bond retention or change of mate and their effects on the breeding biology to be studied. The major contributions to knowledge of the influence of age on the breeding biology and population dynamics of sea birds have been made by Austin (1945) on the Common Tern Sterna hirundo, Richdale (1949, 1957) on the Yellow-eyed Penguin Megadyptes antipodes, Coulson & White (1958, 1960) and Coulson (1966) on the Kittiwake Gull Rissa tridactyla, and Potts (1969) on the Shag Phalacrocorax aristotelis. It is hoped that the present study will make a further contribution to this subject. Studies at the Kaikoura colonies began in 1964 as partial fulfilment for an M.Sc. degree. Quantitative data on clutch size and breeding success with special reference to the effect of age have already been described (Mills, 1967), from information collected in the 1964 65 and 1965-66 breeding seasons. The present study describes the results obtained to October 1969 and incorporates some of the data collected in the first two seasons. The initial part of this thesis is devoted to a general description of the breeding cycle. Later sections examine the factors affecting the breeding biology with special reference to the clutch size and chick survival, the population loss from emigration and mortality and the recruitment to the population from immigration