Habitat and Range of Birds
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Although birds collectively occupy most of
the earth's surface, most individual species are found only
in particular regions and habitats. Some species are quite
restricted, occurring only on a single oceanic island or an
isolated mountaintop, whereas others are cosmopolitan, living
in suitable habitats on most continents. The greatest species
diversity occurs in the tropics in North and South America,
extending from Mexico to South America. This part of the world
is especially rich in tyrant flycatchers, ovenbirds, antbirds,
tanagers, and hummingbirds. The Australia and New Guinea region
has perhaps the most unique groups of birds, because its birds
have long been isolated from those of the rest of the world.
Emus, cassowaries, and several songbird groups, including
birds-of-paradise, are found nowhere else. Africa is the unique
home to many bird families, including turacos, secretary birds,
and helmet-shrikes. Areas that are further from the equator
have less diverse birds. For example, about 225 bird species
breed in the British Isles-about half the number of breeding
species that inhabit a single reserve in Ecuador or Peru.
Despite the abundance of seabirds at its fringes, Antarctica
is the poorest bird continent, with only about 20 species.
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The habitats occupied by birds are also diverse. Tropical
rain forests have high species diversity, as do savannas
and wetlands. Fewer species generally occupy extremely
arid habitats and very high elevations. A given species
might be a habitat specialist, such as the marsh wren,
which lives only in marshes of cattails or tules, or
a generalist, such as the house sparrow, which can thrive
in a variety of environments.
Many habitats are only seasonally productive
for birds. The arctic tundra, for example, teams with
birds during the short summer season, when food and
water are plentiful. In the winter, however, this habitat
is too cold and dry for all but a few species. Many
bird species respond to such seasonal changes by undergoing
annual migrations. Large numbers of bird species that
breed in the United States and Canada move south to
winter in Central or northern South America. Similar
migrations from temperate regions to tropical ones exist
between Europe and Africa, northeastern Asia and southeast
Asia and India and, to a lesser degree, from southern
Africa and southern South America to the equatorial
parts of those continents.
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Habitat
and Range of Birds
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