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Moult of Common Guillemots
Common Guillemot

Verwey (1922) Springmoult from dead oiled birds in Netherlands (N=300) (nov)-DEC-JAN-FEB

Smail, et al. (1972) Birds killed by oil, Jan 1971. 94 Guillemots in breeding plumage had measurements consistent with resident adults of the race Uria aalge californica. 198 birds in winter plumage had mainly measurements and characteristics consistent with dispersing immature birds of the race U. a. inornata (although a few of the smaller birds may have been californica immatures).

Swennen (1977) 31 captive birds 1-3 yrs old, raised from chicks from Scotland. Post-nuptual molt autumn, pre nuptual moult spring. Primaries sometimes moulted twice a year.

Birkhead & Taylor (1977) 9 captive birds, older than 3 yrs, from rehabilitated oiled birds. Primary feathers, jul-AUG-SEP-oct; Secondary, SEP; Head, (jul)-AUG-SEP, JAN-FEB; Tail, (aug)-SEP-OCT-nov; Body, jul-AUG-SEP-OCT-nov.

Hope-Jones & Rees (1985) observations from ships in Irish Sea. Sept adults moulting into winter head.

Harris & Wanless (1990) Birds returning to breeding ledges on Isle of May, therefore replaced flight feathers. Moulting head feathers into breeding plumage oct-NOV-dec N~1300. "The annual proportions of those still in complete winter plumage were significantly, and negatively, correlated with the mean number of days in which sites were visited during the standardised ten-day observation period in mid-October."

Thompson, et al. (1998) Birds drowned in gill nets 1993 (N=24), 1996 (N=104). variation between timing of molt slower in 1993 (El Nino) vs 1996.

Bridge (2004) Swimming efficiency in moulting birds.

Life in air and sea

Guillemots wings are used to fly in two different fluids: water and air. These two fluids require different functional surface-areas for efficient propulsion, (the greater density of water requires a relatively smaller surface area of wing). Therefore, there are competing selection pressures on the Guillemot's wing structure. Guillemots have relatively large wings compared to other paddle-propelled swimmers. They also have high wing-loading (184N/m*m, Ainley et al. 2002) compared to other flying animals. Guillemots also bend their wrists when swimming, reducing the effective surface area by half (Gaston & Jones 1998)

Differences between UK and US terminology

     Plumage                             Plumage
UK   Winter         Pre-breeding moult   Summer      Post-breeding moult 
UK   Non-breeding                        Breeding
US   Basic          Pre-alternate molt   Alternate   Pre-basic molt

Head moult scoring
(1)     (2)
0%      W    full winter plumage
1-35%   W/T  winter plumage, some summer plumage feathers on chin or cheeks (blackish specks)
36-64%  T    transitional plumage (exactly half way)
65-99%  T/B  near summer plumage (progressed moult), some white specks on otherwise blackish head
100%    B    full breeding plumage

(1) Harris & Wanless 1990, (2) Camphuysen 2007

  • Camphuysen, C.J. (2007) "Alcidae: Auks" Technical documents 4.1, Handbook on Oil Impact Assessment, version 1.0, Online version
  • Bridge, E.S., (2004) "The effects of intense wing molt on diving in alcids and potential influences on the evolution of molt patterns" J. Exp. Biol. 207:3003-3014
  • Ainley, D.G., Nettleship, D.N., Carter, H.R. & Storey, A.E. (2002) "Common murre (Uria aalge)", Poole, A. & Gill, F. eds. "Birds of North America" The Academy of Natural Sciences, Philadelphia, Pennsylvania, & American Ornithologists' Union, Washington, D.C.
  • Manuwal, D.A. & Carter, H.R. (2001) "Natural history of the common murre (Uria aalge californica)" pp 1-32 in Manuwal, D.A., et al. (eds) (2001) "Biology and conservation of the common murre in California, Oregon, Washington, and British Columbia. Volume 1: Natural history and population trends"
  • Gaston, A., & Jones, I (1998) "The Auks" Oxford University Press
  • Thompson, C.W., Wilson, M.L., Melvin, E.E. & Pierce, D.J. (1998) "An unusual sequence of flight-feather molt in common murres and its evolutionary implications" The Auk 115(3):653-669
  • Baker K. (1993) "Identification guide to European non-passerines" BTO Guide 24, BTO, Thetford
  • Harris M.P., Webb, A. & Tasker, M.L. (1991) "Growth of young Guillemots Uria aalge after leaving the colony" Seabird 13:40-44
  • Boekelheide, R.J., Ainley, D.G., Morrell, S.H., Huber, H.R. & Lewis, T.J. (1990) "Common Murre" In Ainley, D.G. & Boekelheide, R.J. eds. (1990) "Seabirds of the Farallon Islands"
  • Harris M.P., & Wanless, S. (1990) "Moult and autumn colony attendance of auks" British Birds 83:55-66
  • Tasker, M.L., Webb, A., Hall, A.J., Pienkowski, M.W., and Landslow, D.R. (1988) "Seabirds in the North Sea" Nature Conservancy Commission, Peterborough
  • Harris M.P., & Wanless, S. (1986) "A comparison of the biology of the normal and bridled forms of the Common Guillemot Uria aalge at a single colony" J. Zool. (Lond.) 210:121-130
  • Birkhead, T.R. & Nettleship, D.N. (1985) "Plumage variation in young Razorbills and murres" J. Field Ornithol. 56(3):246-250
  • Cramp, S., ed. (1985) "The birds of the western Palearctic. Vol. 4: terns to woodpeckers" Oxford Univ. Press, Oxford
  • Hope Jones, P. & Rees, E.I.S. (1985) "Appearance and behaviour of immature Guillemots and Razorbills" British Birds 78:370-377
  • Thomas, A. (1984) "Observations sur la mue prenuptiale des Guillemots de Troïl (Uria aalge) de la Reserve du Cap Sizun (Finistere)" Travaux de Reserves SEPNB 2:54–61
  • Harrison, P. (1983) "Seabirds, an identification guide" Houghton Mifflin Co., Boston, MA
  • Croll, D.A. & Holmes, R.W. (1982) "A note on the occurrence of diatoms on the feathers of diving seabirds" Auk 99:765-766
  • Birkhead, T.R. & Taylor, A.M. (1977) "Moult of the Guillemot Uria aalge" Ibis 119:80-85
  • Swennen, C. (1977) "Laboratory research on sea-birds" Netherlands Institute for Sea Research, Texel
  • Smail, J., Ainley, D.G., & Strong, H. (1972) "Notes on birds killed in the 1971 San Francisco oil spill" California Birds 3(2):25-32

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