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There are nearly 10,000 known species
of modern or recently extinct birds. Traditionally,
taxonomists (those who classify living things based
on evolutionary relationships) have looked at bird characteristics
such as skeletal structure, plumage, and bill shape
to determine which birds have a shared evolutionary
history. More recently, scientists have turned to deoxyribonucleic
acid (DNA)-the genetic information found in the cells
of all living organisms-for clues about relationships
among birds. DNA is useful to bird taxonomists because
closely related birds have more similar DNA than do
groups of birds that are distantly related. DNA comparisons
have challenged some of scientists' previous ideas about
relationships among birds. For example, these studies
have revealed that vultures of the Americas are more
closely related to storks than to the vultures of Europe,
Asia, or Africa.
Another method of categorizing birds
focuses on adaptive types, or lifestyles. This system
groups together birds that live in similar environments
or have similar methods for obtaining food. Even among
a given adaptive type, birds show tremendous diversity.
Some of the widespread adaptive types of birds are discussed
below.
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Type
of birds UK cages |