Cowbirds have long been known to lay eggs in the nests of other birds, which then raise the cowbirdsâ€™ young as their own.
Sneaky, perhaps, but not Scarface.
Now, however, a University of Florida study finds that cowbirds actually ransack and destroy the nests of warblers that donâ€™t buy into the ruse and raise their young.
Jeff Hoover, an avian ecologist at the Florida Museum of Natural History, is the lead author on the first study to document experimental evidence of this peeper payback â€” retaliation to encourage acceptance of parasitic eggs.
Findings will be published online in the Proceedings of the National Academy of Sciences March 5.
â€œItâ€™s the female cowbirds who are running the mafia racket at our study site,â€ said Hoover, who has a joint appointment with the Illinois Natural History Survey. â€œOur study shows many of them returned and ransacked the nest when we removed the parasitic egg.â€
So-called â€œbrood parasitic birdsâ€ lay eggs in the nests of host birds that raise the parasiteâ€™s offspring, usually at the expense of some of their own. The brown-headed cowbird parasitizes more than 100 host species, including many Neotropical migratory birds such as warblers, tanagers and vireos. Prothonotary warblers were used for this study because they almost always accept cowbird eggs, Hoover said.
Hosts that use their beaks to grasp or puncture parasitic eggs and remove them from the nest are called â€œejecters.â€ â€œAccepterâ€ hosts raise parasitic eggs.
â€œRetaliatory mafia behavior in cowbirds makes hostsâ€™ acceptance of cowbird eggs a better proposition than ejection,â€ Hoover said. â€œThe accepting warblers in our study produced more of their own offspring, on average, than those where we ejected cowbird eggs.â€
University of Florida Press Release