On the island of Kauai, chickens have not just crossed the road.

They are also crowing in parking lots, hanging out at beaches and flocking in forests.

“They’re absolutely everywhere,” said Eben J. Gering, an evolutionary biologist at Michigan State University who has been studying these truly free-range birds. “They seem to be living a whole diversity of lifestyles, from eating garbage and cat food to being fed by tourists at the beach to foraging on native arthropods.”

In a paper published last month in the journal Molecular Ecology, Dr. Gering and his colleagues tried to untangle the genetic history of the Kauai feral chickens, which turn out to be not only a curiosity for tourists, but also a window into how humans domesticated wild animals. The reservoir of genetic traits could also prove useful for breeders.

Modern breeds of chickens are, by and large, bigger versions of the red junglefowl, a Southeast Asian cousin of pheasants that was domesticated more than 7,000 years ago. (There also appear to be some genes mixed in from the related gray junglefowl.)