Molt of the Ivory Gull

Abstract

-Molting is a fundamental biological process common to all birds, and understanding molt strategies is an integral part of studying any species' life history. Molt of the monotypic Ivory Gull (Pagophila eburnea) has received variable and often contradictory treatment in the literature. Based upon examination of 152 museum specimens, the unique molt strategy of this species is clarified. Juveniles molt directly into definitive (= adult) basic plumage via a complete molt during April to August of their second calendar year. Adults have only a single molt per cycle, a strategy unique among gulls: their prebasic molt starts in March and April, progresses quickly, and is mostly completed before the pre-laying to hatching period (mid June to early August); adults typically suspend primary molt at this time and conclude molt of outermost primaries in late August or September. Thus molt and breeding overlap broadly in the Ivory Gull, presumably an adaptation to the constraints of its high-latitude winter range and the brief Arctic summer. Received iJuly 2001, accepted 12 August 2001.