A songbird is a bird belonging to the suborder Oscines of Passeriformes
(ca. 4000 species), in which the vocal organ is developed in such
a way as to produce various sound notes, commonly known as bird
song. Songbirds evolved about 50 million years ago in the western
part of Gondwana that later became Australia, New Zealand and Antarctica
and later spread around the world.
This 'bird song' is essentially territorial in that it communicates
the identity and whereabouts of an individual to other birds and
also signals sexual intentions. It is not to be confused with bird
calls which are used for alarms and contact, and are especially
important in birds that feed or migrate in flocks.
Other birds have songs to attract mates or hold territory, but
these are usually simple and repetitive, lacking the variety of
many passerine songs. The monotonous repetition of the Common Cuckoo
or Little Crake can be contrasted with the variety of a Nightingale
or Marsh Warbler.
Although many songbirds have songs which are pleasant to the human
ear, this is not invariably the case. Many members of the crow family
make croaks or screeches which sound harsh to humans
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