BACKYARD SECRET: GRAY CATBIRDS SEEM TO RECOGNIZE BROWN-HEADED COWBIRD EGGS

       The brown-headed cowbird does not build its own nest or raise its young.  Instead, it lays its eggs in the nests of other birds and leaves the arduous job of raising its young up to them.

       The brown-headed cowbird lays its eggs in the nests of more than two hundred species of birds.  The list of birds parasitized by this nest parasite includes backyard favorites such as northern cardinals, brown thrashers, and northern mockingbirds.

       In many cases, although their eggs look very different from the eggs of the unsuspecting host birds, the hosts accept them as their own.  As such, they end up raising cowbird hatchlings along with their own young.

       Interestingly, gray catbirds are rarely parasitized by brown-head-headed cowbirds.  Biologists believe this is because, unlike far too many birds, catbirds seem to be able to distinguish color and size differences between their own eggs and those of the cowbird.  As such, when a nesting catbird discovers a brown-headed cowbird egg in its nest, it unceremoniously removes it.

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