Birdhouse

Apart from a bird’s feathering, the beak is often its most striking physical characteristic. But what is a beak made of, what does it do, and what can go wrong with it?

STRUCTURE

The bones of the upper and lower jaw are covered in horny keratin, similar to that found in our fingernails. This keratin layer is technically known as the rhamphotheca—on the lower jaw it is the gnathotheca and on the upper jaw the rhinotheca. Under the microscope the rhamphotheca resembles skin with the deeper layers attached to the periosteum (outer lining) of the underlying bone. The outer layer of the beak is thickened and hardened as its cells contain calcium phosphate and hydroxyapatite crystals.
The rhamphotheca grows out from specialised germinal areas along the top ridge of the beak and along the junction of the beak with the softer skin of the face. These areas are important as damage to them can result in beak deformities.
The cere, the fleshy area around the nares (nostrils) is found only in owls, parrots and pigeons.

FUNCTION

The most obvious function of the beak is eating. Individual species have various shaped beaks reflecting the differences in food types and means of prehension:

• Parrots have a large hookbill reflecting a diet of relatively large
  food items that have to be cracked open to get to the inner contents.
• Finches by comparison have a smaller, softer diet of green grass
  seeds requiring much less force to open.
• Tawny Frogmouths have a wide beak that opens wide enough to
  allow the capture of insects in flight.
• Owls and other birds of prey have a hookbill—somewhat similar
  to that of parrots—designed to tear prey items apart into bite-
  sized chunks.
• Waterbirds such as herons have a long thin beak for ‘spearing’
  small food items, while ducks have a shovel-shaped beak for
  sifting through large amounts of mud looking for food.
  The beak does have other functions apart from eating:
• It can be used as a tactile organ, allowing a bird to explore its
  surroundings by touch.
• It can be used in conditions of extreme duress, as a weapon.
• The colour of the beak can indicate the sex of the bird and its
  reproductive status. It also plays a role in courtship behaviour.
• The Toco Toucan Ramphastos toco—the largest member of the
  toucan family—possesses the largest beak relative to body size
  of all birds. This beak serves several functions ranging from a
  sexual ornament to a refined adaptation for feeding. It also
  offers a significant surface area for heat exchange, regulating
  heat distribution by modifying blood flow and therefore acting as
  a transient thermal radiator.
• The beak appears to play a role in a bird’s sense of smell. Kiwis,
  for example, locate their food by ‘smelling it out’ in leaf litter, but
  other birds such as vultures adapt their beak use to their food
  supply.
• The beak may play a role in migratory birds orientating themselves
  to magnetic north through iron-containing receptors in the upper
  beak.
  To assume that a beak is used only for eating (and biting bird keepers!) is to vastly understate its role in a bird’s life. Any problems with the beak will therefore have a great impact on a bird’s lifestyle.

  Problems

  With a structure as versatile and complex as a beak, it stands to reason that things can (and do) go wrong with it. Following are just some of the problems I have seen with beaks.

  MALFORMATION

  Wry/Scissor Beak
  This problem occurs when the upper beak is deviated to the side, either from the level of the cere or from the beak tip.

  Author:
  Dr Bob Doneley
  BVSc FACVSc (Avian Health)

  The full article you can read by purchasing Australian Birdkeeper magazine Vol 23 Iss 3 from
  www.birdkeeper.com.au
  Reproduced with permission from ABK Publications
  and Australian BirdKeeper ©2011