Dress Code

, 02 January 2024
Dress Code
Golden Plover - breeding (summer) and winter plumage © Nigel Symington

By James Duncan

Communities & Wildlife Officer

Throughout autumn millions of birds have been winging their way overhead on route to a vast array of wintering grounds. With the arrival of astronomical winter, many of these migrants, plus a lot of resident species, will be sporting a wholly different outfit from that exhibited during the warmer months. Much like us Homo sapiens getting all dressed up for a fancy night out, birds typically require an extravagant costume to increase their chances of attracting a member of the opposite sex. Of course, like many things in nature, the mechanism for this isn't entirely straightforward. 

Put simply, feathers, containing keratin, are unable to heal from damage without being replaced. The process responsible for this replacement is called moult. This has a couple of functions; creating healthy feathers essential for flight and providing a new look to a bird's plumage - colours and patterns that may indicate its age, sex and the season. Whether by species, by individual, by time of year or even by individual feather, its complex nature is critical for survival, insulating the body from elemental extremes and acting as a catalyst for changes that determine whether a bird will reproduce. 

Black-necked Grebe & Great-crested Grebes in Breeding plumage
Black-necked Grebe & Great-crested Grebe in Breeding plumage

Moult may take two different forms, either complete or partial. These do exactly what they say on the tin, 'complete' indicative of a bird replacing every one of its feathers over a moult cycle, whereas a smaller selection may be replaced during a 'partial' moult (perhaps just flight or body feathers). Replacing these feathers is a mighty expensive process though, that is, expensive of energy. Moult needs protein and an awful lot of it. It therefore makes sense to avoid moult at times when energy is in particularly high demand, namely during breeding and migration. Its timing is crucial and the larger you are the more complex it becomes - larger species may take twice as many weeks to moult as smaller ones. Typically most birds will comply to one of three overall strategies per year - one complete moult, one complete and one partial or two complete moults. For example, the Willow Warbler is one of the very few British birds that undergoes two complete moults each year.

Environmental factors have a huge part to play in feather degradation, whether this be courtesy of the sun's ultraviolet radiation or wear and tear as birds move through abrasive vegetation. Of course, lengthy journeys of flight also wear out feathers and those birds that fly further simply tend to replace more of them. With these harsh environmental considerations, what's the logic behind 'expensive to produce' brightly coloured breeding plumage? To reiterate, it comes down to sexual selection. As with 'makeup' to us, beautiful feathers are mighty attractive to other birds, promoting health, virility, status and dominance - things that'll ultimately decide who gets to mate and who doesn't. 

Black-headed Gull - summer / winter plumage
Black-headed Gull - summer / winter plumage

Owing to the physical demands required for obtaining such dazzling colours, it makes sense that should a bird have an easier and less demanding winter, it'll be more brightly coloured in the summer. Thus, there are serious considerations for the acceptability of winter habitat - the quality and abundance of available food, the suitability of shelter and the risk of potential predation. Much like humans converging on a desirable location to live, birds will flock to areas with the best habitat, typically those that offer stability of resources over long periods of time. 

Black-throated Diver - Breeding (summer) plumage © Roger Wilmshurst
Black-throated Diver - breeding (summer) plumage © Roger Wilmshurst

There happens to be another process, working in conjunction with moult, that changes the appearance of a host of birds throughout the year. It seems rather counterintuitive as it creates brighter plumage, but is actually a form of wear, known as feather abrasion, which follows a complete moult. Essentially, the tips or fringes of the replacement feathers are coloured differently from the rest of the feather. As they abrade throughout the winter the breeding colours are slowly exposed, negating the need for an expensive moult but ensuring the plumage is at its most resplendent come spring. StarlingChaffinchStonechat and Reed Bunting are all species that subscribe to this strategy, amongst a huge array of others.  

Stonechat - fresh Autumn plumage and post feather abrasion in Spring
Stonechat - fresh autumn plumage and post feather abrasion in spring

So, which is the most dramatic costume changer amongst British birds? Well, you'd have to say that top prizes would likely be split amongst the Ducks - ShovelerPintailTeal; the Grebes - Great-crested, Black-necked and Slavonian; the Divers - Red-throated, Black-throated and Great Northern; and the Wading BirdsGolden PloverGrey PloverKnotCurlew SandpiperBlack-tailed GodwitBar-tailed Godwit, Spotted Redshank and the Phalaropes. However, when it comes to extravagant attire, the Ruff really can't be beaten with its flamboyant ruff and ear tufts. The breeding plumage may even come in an array of colours, be it black, white or ginger. It should however be noted that the Ruff is no longer a regular breeding species in Britain and is observed mainly during autumn migration and winter. Regrettably for us, the vast majority of these birds don't breed in Sussex so we rarely get to appreciate the fancy dress in all its glorious variety. 

Ruff - Breeding plumage © Roger Wilmshurst
Ruff - Breeding plumage © Roger Wilmshurst
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Comments

  • Dorothy MCDONALD:

    Wonderful articles and pictures. As always I’m fascinated with birds and can’t thank you enough for these e-mails. DMcD

    11 Jan 2024 14:49:00

  • Sussex Wildlife Trust:

    Thank you for your lovely comment

  • Adge Roberts:

    Good to see you are still taking great pictures Roger

    11 Jan 2024 17:11:00

  • Glynis:

    Very interesting, I didn’t know about abrading, thanks James

    12 Jan 2024 08:24:00

  • Jill Hobbs:

    An excellent and informative article. I never knew quite how the male birds managed to look so magnificent at this time of year.

    13 Jan 2024 06:50:00

  • Frances Horton:

    Awesome photographs! It’s wonderful that various photographers have caught excellent images of these birds to illustrate James’s text.
    Thank you so much James for the commentary and information about how and why birds change their plumage. I didn’t know any of that, and it’s so good to learn something new. Although I live in Auckland, New Zealand, I’m of British descent and spent several happy years in England. This brings me closer to my origins, and I value it !

    14 Jan 2024 08:47:00

  • Sue Whall-Poole:

    Excellent, thanks so much, Sue

    17 Jan 2024 15:46:00