Brown-headed cowbirds cannot incubate their own eggs. Instead, they lay their eggs in the nests of other birds, who incubate them and raise the cowbird chicks as their own. According to a new study by Jeff Hoover of the Florida Museum of Natural History published in Proceedings of the National Academies of Sciences the cowbirds have an interesting way of ensuring their offspring will be treated well: extortion.
Feathers Bonmarito, a top earner amongst the cowbird capos...
After a cowbird lays her egg in another bird's nest, she returns frequently to check on the status of her chick. Hoover has found that if the cowbird returns to find her egg missing, she is highly likely to destroy the other bird's nest completely including the bird's eggs.
This is called "mafia behavior" by scientists and had been witnessed in cuckoos before, but never brown-headed cowbirds.
Victims of the "Arbor Day Massacre"
Such behavior has led to speculation that perhaps the surrogate bird raises the cowbird's chicks at least partially out of fear of the cowbird's wrath. Warblers, for example, have never been witnessed removing cowbird eggs from their nests. (In order to conduct the experiment, Hoover had to remove the cowbird eggs when the warblers were away).
Warblers questioned about the cowbirds' behavior claimed unanimously not to have seen anything, and that they had nothing but deep respect for cowbirds, the upstanding pillars of their community.
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