Establishment and development of a seabird colony: long-term trends in phenology, breeding success, recruitment, breeding density and demography

Few studies document long-term colony-level metrics from colony establishment to maturity (equilibrium) and few test predictions of general models of colony development. We describe long-term trends in a colony of Australasian Gannets (Morus serrator) which has been monitored from an early stage in its development. The colony at Pope’s Eye, within Port Phillip Bay, Victoria, Australia was established in 1984 on an artificial structure and the first nest count (25 nests) was conducted in the same year. The colony was then studied for 15 of 19 years between 1988 and 2006–2007. During the study, 2,516 eggs were recorded, resulting in 1,694 chicks hatching (67 % of eggs), of which 1,310 (77 % of those hatched) fledged. At least 184 (14 %) of fledged offspring returned to Pope’s Eye as breeding adults. Since establishment, the number and density of nests increased (number of nests increased 8.8 % annually), with density increasing at varying rates in different areas of the colony. Early recruitment involved birds from a nearby colony, but within 5 years post establishment the first natal recruits were breeding at Pope’s Eye and thereafter natal recruitment was the main source of new breeding adults (totalling 81.4 % of all recruits). Age of recruitment varied throughout the study, though not systematically, and there was no difference between the sexes. The pattern of rapid initial growth is typical of patterns reported for other seabird colonies. However, as the colony (and birds within it) aged, there was no increase in breeding success and egg laying did not become earlier, as was expected from general models of colony development.