Cowbirds: Unwelcome Nest-Guests

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Photo courtesy MOTHER EARTH NEWS
Cowbirds are birds that should be watched for.

In March, a small relative of blackbirds and grackles that
lives year-round in the southern U.S. but spreads north in
spring may become quite noticeable on the ground in fields
and pastures. Named for their feeding habits, cowbird
flocks often gather near horses and cows to feast on the
insects those animals attract. But the cowbird’s behavior
at nesting time is what has earned it its fame — or rather,
its notoriety.

Male cowbirds are about seven inches long with a brown head
and neck the rest of the body is black and iridescent. The
all-gray female is less distinctive, but she can typically
be seen flocking with the males.

The cowbird can seem a rather comical creature with a slow,
awkward walk and often upraised tail.

Less amusing is the cowbirds’ habit of laying their eggs in
the nests of other birds. Most birds need 20 minutes to an
hour to lay an egg, but the female cowbird takes less than
a minute; she leaves her egg in secret while the nest’s
rightful owner is away. The unwitting nesters will usually
accept the cowbird egg and raise the baby cowbird as their
own.

Unfortunately, cowbird eggs hatch sooner than the eggs of
other species and the young cowbirds grow quickly, using
their size to their advantage in getting more food from the
parents. This cowbird parasitism is actually endangering a
number of species of birds.

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