Cowbirds are despicable. I would like to put this in better terms, but despicable is the only term of appropriate strength.
In more sciency (my own term) language, cowbirds are something called “brood parasites.” This means that mature cowbirds lay their eggs in the nests of other bird species and then allow the other birds to hatch and raise their young.
Cowbirds are not particularly fussy about who raises their young. Any songbird species will do. The host birds will sometimes raise the cowbirds at the expense of their own brood. Cowbirds are often conspicuous, if not grotesque, in comparison to the birds raising them. Posted is a photograph (thanks to Audubon) showing a tiny warbler feeding a gigantic cowbird.
According to Matt Soniak, as found in his online article at www.audubon.com titled How Does a Cowbird Learn To Be a Cowbird?, the most interesting point in all of this is that a cowbird remains a cowbird, even after being raised by another species.
That really is something.
You might think a cowbird raised as a chickadee would assume the habits of a chickadee, but this does not happen. Consider how humans exposed to the same conditions of upbringing might respond. An identity crisis might result. A certain segment of humans enduring such upbringing would require extensive therapy to (pun intended) fly right.
Recent research has discovered part of what helps a cowbird learn to be a cowbird. Juvenile cowbirds—ever despicable as their parents—sneak out of the host family natal territory (nesting area) at sundown to roost in open fields. There, they find other cowbirds to hang with during the night. Probably, this is a rough equivalent to our rowdy teenagers joining a gang. In the morning they return for breakfast with their foster family. Eventually, the birds abandon the family that raised them and do only cowbird things.
Additional research revealed that, to some degree, adult cowbirds monitor their young in the nests of the birds raising them. The success or failure of certain host species may impact the choice of future nests. One researcher, Mark Hauber, contends that the adults may even initiate limited contact with their young. They may try to make certain cowbirds become cowbirds.
Posted below is a photograph of an adult cowbird.