Abstract

In 1977 and 1978, silver gulls on Carnac I., near Perth, W.A., bred continuously from March to November, with laying peaks in April, June and August-September. Many pairs laid several times during the year, showing complex patterns of replacement and post-refractory clutches. This prolonged breeding appears to have resulted from sustained predation pressure in an environment with few climatic or food constraints. Intra-clutch egg variation and seasonal changes in clutch and egg sizes followed the patterns common among gulls. Egg sizes in clutches laid by the same individual were very similar, irrespective of time of year.