Page 130 - A Field Guide to Fairfax County's Plants and Wildlife
P. 130

Birds are a class of warm-blooded vertebrates with feathers for insulation
and flight. All modern birds have forelimbs modified into wings, a toothless
beak, lightweight hollow bones and other unique adaptations for flight
(although not all birds fly). Like reptiles, birds reproduce by laying eggs that
are surrounded by a protective shell.

Some birds travel long distances during certain seasons of the year. These
seasonal journeys are usually driven by food availability and breeding.
Many North American species rely on food sources that are not available
during the cold months, such as fruits, insects and nectar from flowers. In
the fall, these species migrate south to tropical areas and stay through the
winter. As temperatures warm in the spring and food becomes plentiful
again, they migrate back north to breed and raise their young. Not all bird
movements are true migrations; some species or populations move from
place to place during certain seasons, but only travel as far as they need to
find food and/or suitable habitat. Species or populations of birds that are
non-migratory are called residents.

Because birds are colorful animals, the descriptions in this section
emphasize colors and markings on certain parts of the body. In some
species, the male and female birds are similar in appearance, while in other
species the sexes look different.

Birds are more often heard than seen, so knowing what they sound like
can help you to identify them more quickly. Birds vocalize in two different
ways. Songs are long musical phrases usually produced by males to define
breeding/nesting territories during spring and summer. Calls are less
complex, mostly just a few short notes. They are uttered by both sexes and
can be heard throughout the year.

Fairfax County is home to a diverse range of species including songbirds,
birds of prey and migratory waterfowl and other coastal birds.

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