Victimised birds inherit attacks

Brood parasitic birds, which place their eggs in a nest for other birds to care for, can act like an inherited disease, affecting future generations of the birds they victimise.

Brood parasitic birds, such as cuckoos and cowbirds, remove the eggs of birds from the nest and replace them with their own eggs, sometimes forcing the foster parents to accept the substitution through [violent behaviour]. New research from The University of Auckland has also shown that daughters of parasitised warbler mothers are even more prone to the actions of parasitic birds, although these females use different nest boxes across years.

"Brood parasitic birds are much like other parasites and pathogens, reducing the reproductive success of the birds they victimise," says Dr Mark Hauber of the Faculty of Science. "However, this recent study seems to suggest a longer term consequence on affected individuals, infecting subsequent generations with the same problem. This creates lineages of warbler families unable to escape the cost of parasitism whilst other families are not affected. In the longer term, social history will circumvent an evolutionary need to reduce parasitism, because the population may become dominated by individuals that always escape victimisation."

The research, funded by the US Fish and Wildlife Service, the New Zealand Marsden Fund, and the National Geographic Society, and conducted in collaboration with the Illinois Natural History Survey, studied prothonotary warblers Protonotaria citrea and brown-headed cowbirds Molothrus ater in Southern Illinois over a period of twelve years. The findings are published in the Journal of Animal Ecology. 

Editor's Note: Original news release can be found here.