Summary Williams, A. J., Hockey, P. A. R. & Cooper, J. 1984. Aspects of the breeding biology of the Kelp Gull at Marion Island and in South Africa. Ostrich 55:147-157. The breeding biology of the nominate race, Larus d. dominicanus, of the Kelp Gull at Marion Island, in the subantarctic, is compared with that of the race L. d. vetula in South Africa. Both populations have similar clutch size and intraclutch egg-size variation, lay eggs of similar composition, and their chicks have similar growth patterns. The offspring-reduction strategy (involving variation in egg size within the clutch, and asynchronous hatching) is also similar in the two populations. The Marion Island population is smaller in adult and egg sizes, has a slower chick growth rate, and a lower egg mortality than L. d. vetula. These differences are attributed to the differing feeding ecology of the two populations, in particular to the fact that only the Subantarctic population faces competition for resources from the Subantarctic Skua Cat...