In doing a little research about cowbirds, I found this:
Some species may simply build a new layer over the bottom of the original nest. Brown-headed cowbird nestlings are sometimes expelled from the nest. This rejection, however, may trigger a "mafia" reaction, according to a study by the Florida Museum of Natural History. When the parasitic egg was removed from the host nest, the cowbird returned to ransack the nest about 56% of the time. In addition, the cowbird also destroyed nests in a type of "farming behavior" to force the hosts to build new ones. The cowbirds then laid their eggs in the new nests 85% of the time.
Next thing you know, HBO will be replacing The Sopranos with a show about cowbirds in therapy.