Birds can act like gangsters who threaten shopkeepers who fail to pay "protection money," a new study says. The study focused on the brown-headed cowbird. Females of the species lay eggs in the nests of other bird species, leaving the strangers to incubate and raise the cowbird chicks—or have their nests attacked. Brown-headed cowbirds "can lay their eggs within ten seconds," said avian ecologist Jeffrey Hoover of the Illinois Natural History Survey, who led the new study. "It's quite amazing how fast they are" compared with other birds. This cowbird, the main "parasitic" bird species in North America, depends completely on other birds to raise its young—or else. Cowbird mothers keep watch on the nests where they've laid their eggs. If the birds find that their eggs have been destroyed or removed from the nest, the cowbirds retaliate, the study says. The birds reportedly destroy the host birds' eggs, pecking holes in them or carrying them out of the nest and dropping them on the ground.