Avian - Feathers

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Introduction to Feathers

  • Feathers are a uniquely avian trait
    • it is now well established that feathers also occurred in dinosaurs
    • In the 1990s feathers were described in a series of non-avian coelurosaurs, mostly from the Chinese Liaoning deposits
  • Feathers are what enable birds to fly
    • thought to have evolved as a thermoregulatory device
  • Feathers are lightweight but strong
    • the surface is made up of tightly spaced, overlapping filaments that hook together
    • overlapping feathers form the wings which birds fly
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Types of Feather

  • For example
    • Vaned or contour
    • down
    • semiplume
    • filoplume
    • bristle
    • powder down
  • There are two main categories of feathers
    • Plumaceous - downy for insulation
    • Pennaceous - linked, vaned feathers. Wing and contour feathers.
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Feather Structure

  • Made of keratin
    • an inert substance that consists of insoluble microscopic filaments embedded in a protein matrix
    • also found in hair, nails, claws and scales of other animals
    • bird keratin is unique and differs from that of modern reptiles
  • a contour feather has a long central shaft and a broad flat vane
    • the hollow base of the shaft (quill) anchors the feathers to the follicle under the surface of the skin
    • the rest of the shaft (rachis) supports the vanes
    • branching of the rachis are barbs
    • each barb has barbules projecting either side that interlock with the barbules of adjacent barbs
    • barbs and barbules form an interlocking, but flexible, surface
  • vane of a typical body feather consists of a hidden downy base (for insulation) and an exposed cohesive outer portion (for streamlining)
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Feather Structure: Pennaceous Feathers

  • give birds a streamlined shape, protection from moisture, and the ability to manoeuvre freely in the air
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Feather Structure: Plumaceous Feathers

  • the body feathers of most birds include an aftershaft that emerges from the underside of the shaft where the first basal barbs of the vane branch off
  • the aftershaft is almost always downy
    • functions to increase insulation
    • in the ptarmigan winter plumage, the aftershaft is 3/4 as long as the main feather
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Other uses for feathers: Make Sounds

  • male club-winged manakins
    • use the feathers as mating calls as part of an elaborate dance
    • when the feathers rub against each other they make a high-pitched sound
    • the feather vibrates at 1500 cycles per second, stridulation
  • male American woodcocks clap their wings fast high in the air which creates twittering sounds
    • have narrow gaps between their feathers which create the sound
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Other uses for feathers: Reduce sound

  • Owls
    • 3 feather features
      • comb-like structures where the air first hits the wing, reducing the turbulence and overall noise
      • on the trailing edge, there are wispy fringes which scientists thinks help smooth airflow
      • soft-velvet covering on the top of the wings
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Other uses for feathers: Hearing

  • facial discs in owls
  • the feathers reflect sound which help them pinpoint soft noise
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Other uses for feathers: Digestive Aid

  • Grebes eat their feathers to slow digestion and stop fish bones etc. damaging their digestive tract
    • feathers can fill up half the gizzard
    • don't swallow stones like other birds
    • the pyloric pouch is where the smaller feather ball filters out sharp bones
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Other uses for feathers: Fishing

  • form an umbrella which it then hunts under
  • thought the shade could either reduce glare or draw fish in, or scare away smaller fish and leave medium and large fish
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Other uses for feathers: Water transport, snowshoe

  • Water Transport
    • Sand grouse use specialised belly feathers to transport water back to their young
    • a single bird can pick up 40ml
    • when wet the feathers such in water
  • Snowshoes
    • the feathers quadruple the area of their foot which makes it less likely to sink into the snow
    • thought to reduce the sinking by half
    • save energy while travelling
    • some species grow these feathery snowshoes every year
  • Courtship displays
    • birds of paradise
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