Story of the Cowbird

Ever since our visit to Costa Rica two years ago, I have been much more interested in the animal kingdom and the birds in our backyard.  First, thanks to incredible naturalist and sis-in-law Sherry, we got a book called Tropical Nature: Life and Death in the Rain Forests of Central and South America, by Adrian Forsyth & Ken Miyata.  https://www.google.com/books/edition/Tropical_Nature/_EW9CLmu54QC

Among many others, it told the story of cowbirds, who put their eggs in other birds nests so the other birds will have the burden of raising the young.  The cowbird eggs hatch sooner and the young are aggressive so they survive well in this arrangement.

Well, on our feeder out back, we noticed unusual behavior.  A juvenile looking bird fluttered its wings repeatedly to get its mother to feed it, and the mother did, although was smaller and looked nothing like the young bird asking to be fed.  Our bird book finally helped us identify the young one as a cowbird and plainly this was an adoptive nest situation!

Back to "Tropical Nature"for a fascinating riff on this.  In the rainforest, cowbirds often put their eggs in Oropendola nests (http://en.wikipedia.org/wiki/Oropendola).   The book explains that the Oropendolas are troubled by flies that lay their larvae on the eggs; the larvae then burrow into the eggs and kill all the Oropendola chicks.  Well, recall that the cowbird eggs hatch sooner.  So where cowbird eggs have been put in Oropendola nests, the cowbird chicks hatch before the larvae have made much progress, and the chicks then eat the larvae that have been placed on the other eggs.  So notwithstanding the cowbird awful reputation for sponging off of others,  the Oropendolas are far more successful breeding when cowbirds hijack the Oropendola nests with their eggs.