Moult and autumn colony attendance of auks
Harris M.P., & Wanless, S. (1990) British Birds 83:55-66
Adult Guillemots Uria aalge returning to the Isle of May, Firth of Forth, from early October were in winter plumage, but soon started to moult, and by early December 50% were in full summer plumage, which was then kept until late July. The time needed for the post-breeding moult and the time spent in winter plumage totalled about 88 days; the pre-breeding moult took about 43 days. Many British Guillemots spend only a short time in winter plumage, but it is unclear whether this is a recent phenomenon. In contrast, most Razorbills Alca torda still spend three to four months in winter plumage and have their pre-breeding moult in late winter and spring. Some Black Guillemots Cepphus gylle also visit colonies, and come into breeding plumage in the early winter, whereas Puffins Fratercula arctica are flightless in the late winter and do not attain summer plumage until the spring.
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