The Relationship between Moult and the Reproductive Cycle in a Population of Crested Terns, Sterna bergii Lichtenstein

Abstract

In a population of crested terns breeding in the Fremantle area of south-western Australia, a proportion of adults were moulting in all seasons. At the individual level moult was protracted over the period of gonadal quiescence (39-41 weeks) with little overlap between the alternate moults of the cap and the basic moult. Wave moult was observed in the replacement of the primary feathers. Plumage state was a reliable indicator of gonadal condition in females at all times of year, but not in males while they were involved in the nesting cycle. The plumage states observed in the population reflected the prolonged breeding season with bimodal peaks of laying characteristic of the area, but the moult patterns of marked individuals suggested that moult was essentially aseasonal and continuous.