Migration

• Migration is the journey made twice a year between
  a summer breeding area, where food is plentiful,
  and a wintering area with a good climate.
• Many migrating birds have to build up fat stores
  to allow them to fly non-stop for many days without food.
• A migrating bird can fly across the Sahara Desert
  in 50-60 hours without stopping to ‘refuel’.
• Birds find their way by observing landmarks,
  the patterns of stars and the position of the setting sun.
  They also can monitor the Earth’s magnetic field.
• Most birds that migrate long distances fly at night.
• The snow goose migrates nearly 5000 km south
   from Arctic Canada at an altitude of 9000 m.

Songs and Calls

A box-shaped organ, Syrinx lies at the bottom end of the bird’s
windpipe where divides into the two tubes which lead to lungs.
Within the Syrinx, each of these tubes can be closed completely
or partially by a pair of fleshy lips. When the bird contracts its lungs,
a jet of air is blown through each pair, creating a musical sound.
Muscles within the Syrinx enable a bird to vibrate each pair of lips
independently and so vary the pitch and quality of the note that
comes from each pipe. The longer the windpipe, the deeper the sounds.

Cranes, which produce trombone-like calls, have windpipes
that are so long they curl into loops.

Canaries, when trilling, create 90% of the sound with the left
tube and use the right mainly for breathing.

The two sounds from the two tubes may also combine and
interact with one another to create a quite different sound.
This explains how some birds, such as parrots and mynahs,
are able to  imitate human speech.
 

Bird colors

Some of the colors of feathers come from melanin. A pigment
that human beings produce in their skin when exposed to the sun.
Melanin creates the black of a blackbird’s feathers but also,
in different varieties and strengths, browns and yellows.

Reds and oranges area created by pigments called carotenoids.
These, a bird has to obtain directly or indirectly, from plants.

Flamingos and scarlet ibis derive them from small crustaceans
which in turn get them from the blue-green algae on which they feed.

Other colors are created not by chemical pigments but physical
structures within the feathers.

The blue of a jay’s wing feathers is created by microscopic
bubbles in the keratin of the feathers which refract the light.
So such a feather will not look blue but brown if light shines
not on it but through it.

• Feathers are made of a protein called keratin.
  Human hair and nails are also made of keratin.
• Feathers grow at a rate of 1-13 mm a day.
• The hummingbird has about 1000 feathers,
  while the swan has 25,000.
• A bird’s feathers are replaced once or twice a year
  in a process that is known as ‘moulting’.
• Feather’s keep a bird warm, protect its skin, provide
  a flight surface, and may also attract mates.
• In most birds, a third of the feathers are on the head.
• The 7182 feathers of a bald eagle weighed 677 g,
  more than twice as much as the bird’s skeleton.
• Birds spend time every day ‘preening’ - cleaning
  and rearranging their feathers with their beaks.