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Sensible clothing for birds. Soft strong and very long-lasting!
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 Just how many feathers
does a bird have? This is a tricky question to
answer because birds have many more feathers that just those that form
their visible outer plumage. In broad terms, they have three main
types. Close to the skin, down feathers keep their bodies warm.
Effectively they live within a duvet or, commemorating man's use of bird
plumage for our own benefit, an eiderdown. Down plumage is soft and
fluffy. Ducklings and the young of many other species are entirely
'downy' and, given their aquatic lifestyle, adult waterfowl possess more
warm, insulating down plumage that any other group of birds.
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Contour feathers cover
all the external areas and overlap each other to fulfill a range of important
functions. They keep the bird warm, provide a waterproof seal and streamline
it for flight. The feathers of the wing and tail are the longest, stiffest
and most hard-wearing. These are the feathers that create and sustain
movement through the air. Instead of the cliché, 'as light as a
feather' it is probably more apt to say 'as strong as a feather' when
considering the vast distances flown by birds. Furthermore, once airborne,
most propulsion is provided by a key group of only 10 'primary' feathers
the long, finger-like feathers arranged to form the wing tip.
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Where does a feather's
strength come from? The typical flight feather consists of a long, central
tapering shaft. Evidence of weight-saving is everywhere. The shaft is
hollow and the vanes are held together by an intricate interlocking lattice
of barbs and filaments that hook together and branch outwards from the
feather shaft. This sounds complicated but the concept is similar to the
design of a zip fastener. Birds preen by running the bill tip lengthways
along the feather. Part of what they are doing is sorting each feather
back into shape by re-zipping any separated vanes back together, making
sure that there are no gaps or breaks and that the feather is fully serviceable.
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 Some
species have a preen gland located at the base of the tail and anoint
themselves with a resin that keeps them waterproof or, in the case of
waterfowl and seabirds, buoyant. Herons have special 'powder down' feathers.
The feathers grow continuously in scattered groups and break down at the
tip to produce talc. Preened into the plumage, this gives heron feathers
a bloom or shiny lustre and also adds a waterproof dressing. Male linnets
acquire distinctive red breeding plumage around the head and chest not
by replacing feathers, but by wearing off pale tips and revealing a bright
underlying colour. Some other seed-eating birds use the same method of
exchanging a dull winter plumage for a bright summer one. However, this
is the exception rather than the rule and, even with the best care, the
vast majority of birds have to replace (moult) all their feathers each
year
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For species that perform
globetrotting annual migrations the timing and
duration of moult is critical. Arctic terns commence their great annual
trek from the edge of the Antarctic to the high latitudes of the
Northern Hemisphere early in the new year and do not reach breeding
areas until late spring. By the end of summer they must leave to return
south. Only when they arrive back off the coast of the Antarctic
Continent do they moult. The process of feather replacement is gradual
and takes about 60 days to complete. During it the birds still need to
fly and dive for fish - so at no time can they afford to be flightless.
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 Wildfowl
are one of the few groups of birds that opt for a short, rapid moult of
all their flight feathers at once. Consequently, for nearly a month they
are scarcely able to fly; a risky business in the natural world. Shelducks
prefer safety in numbers and almost the entire north-west European population
migrates to the vast mudflats of the Elbe-Wesser estuary on the southern
shores of the North Sea to moult. Flocks leave the British Isles in July
and have been tracked crossing the Pennines at a height of over 1,000
meters. Adults looking after broods of young are unable to travel and
must moult locally while attending crèches.
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 Gulls
take up to four years to change speckled brown immature plumage to the
smart plain monochromes of adulthood. Most species are common and approachable
and, while their immature plumage may look complex, it can provide an
insight into how feathers wear.
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Sunlight acts adversely
on the pigment of feathers, but at a differential rate: it fades pale
plumage more rapidly than dark. Immature gull feathers are a mixture of dark
and light and, by mid summer, are so heavily worn that pale tips, spots
and fringes may
be completely abraded, leaving just dark bases behind.
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So, getting back to
the original question, how many feathers do birds have? The total number
of contour feathers is related to a bird's size. The larger the bird,
the greater the number. For big species like swans this works out in the
region of 25,000 individual feathers. What species has the least? The
title goes to hummingbirds, some of which have as few as a hundred.
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