Don't Lay Your Eggs All in One Basket: Brood Parasitism as a Survival Strategy.

ica (printed in stages during 1827–1838) by American ornithologist, naturalist, and painter John James Audubon (1785–1851), shows a pair of oft-vilified brown-headed cowbirds. This painting appears in the book as one of 435 life-sized watercolors that were reproduced from Audubon’s hand-engraved plates. In this painting, he portrays the birds frozen in act of foraging, a technique he honed from observing birds where they lived. Audubon’s own words best describe the work: “Male with the head and neck sooty-brown, the body black, glossed with green, the fore part of the back with blue. Female considerably smaller, greyish-brown, the lower parts lighter.” The genus of this bird, Molothrus ateras well as the bronze-headed variant Molothrus aeneuscomes from Molothrus, the Greek work meaning vagabond or parasite. Although there are other bird species that prey on the parental skills of their feathered neighbors by laying eggs in their nests, only birds of those two species practice obligate parasitism in North America, placing them among approximately one percent of avian species worldwide. Before cowbirds—which are also variously known as cow-pen birds, cow buntings, or buffalo birds—followed cattle, they tracked bison herds across the Great Plains, where they were sustained by the copious insects. Naturalists have ventured that cowbirds adapted to this nomadic existence by becoming brood parasites and depositing their eggs in nests built and incubated by birds of other species. Incubation for birds is analogous to pregnancy for mammals, providing warmth, protection, and food to the developing embryo. This process can involve establishing and defending a territory, nest building, and collecting food