Hawaii’s free-ranging chickens: fair or feral fowl?

Chickens roam the Hawaiian island of Kauai, and people disagree about where these birds came from. Sure, this sounds like just another tongue-in-cheek joke about the origin and movements of the world’s most common bird, but it’s a question with real conservation import.

Some people say the birds are escaped domestic chickens and view them as invasive pests to be eradicated. Others believe they descend from red junglefowl, the domestic chicken’s wild ancestor, brought by Polynesian settlers to the islands over 800 years ago. They see the free-ranging chickens as part of the island’s Polynesian heritage to be preserved.

In a study published last month in Molecular Ecology, researchers turned to DNA to illuminate the debate. They analyzed genetic material of 23 chickens from eight different areas of the island, and made notes on plumage, leg color, and vocalizations of 21 additional birds.

Most of the birds on the island look like wild red junglefowl, with striking red, black, and green plumage. A few are speckled with white and reddish-brown, the colors characteristic of most domestic breeds. These plumage patterns tend to match the birds’ calls: those kitted out like red junglefowl also crow like the wild birds, while birds with more chicken-like plumage sound roughly like domestic chickens.

But genetics tells a more complex story. Analysis of the birds’ mitochondrial DNA, which is inherited only from the mother, reveals that two different lineages of chickens are present on the island. The researchers identified 20 birds that belong to a tribe called haplogroup E, similar to European-derived domestic chickens. Only 3 belong to haplogroup D, allied with red junglefowl from Asia and similar to specimens from archaeological sites dating prior to European contact.

You can’t judge a chicken by its feathers, it seems. The ancient Polynesian mitochondrial lineage is rare, but wild red junglefowl plumage is common, meaning that some birds with the wild appearance actually represent a domestic maternal line. That’s surprising, the researchers say, because usually hybrids of red junglefowl and domestic chickens look more like the domestic birds.

Legally speaking, Kauai’s free-ranging chickens have a complex, contradictory status: state law protects the birds in natural areas, but those in developed areas are considered pests. Yet analysis of a large number of markers across the genome shows that all the birds are part of a single, continuous population.

This population has lots of genetic diversity, with genes of both domestic and wild origin, and probably resulted from interbreeding of escaped domestic chickens with wild red junglefowl. In other words, the birds on Kauai are like Schrödinger’s chickens, simultaneously wild and invasive.

Red junglefowl and domestic chickens are members of the same species, Gallus gallus. Domestic chickens are the most numerous birds on the planet, but wild red junglefowl are considered threatened across much of their native range in Asia.

Interbreeding with escaped domestic birds is thought to be a major threat to red junglefowl. The new study both confirms that this is a problem and offers a possible solution. Because they bear ancient DNA, the researchers say, Kauai’s feral birds represent genetic reservoirs that could aid conservation of wild red junglefowl. These genes might also help improve domestic breeds.

Studying Kauai’s chickens could help illuminate broader issues in ecology as well, such as what determines how and why invasive species become established in a new area, and what happens genetically when a domestic species goes feral.

But as to whether Kauai’s free-ranging chickens should be conserved or eradicated, that question remains as unanswerable as, well, chicken versus egg. – Sarah DeWeerdt | 7 April 2015

Source: Gering E. et al. 2015 Mixed ancestry and admixture in Kauai’s feral chickens: invasion of domestic genes into ancient Red Junglefowl reservoirs. Molecular Ecology DOI: 10.1111/mec.13096

Header image: Wild roosters have distinctive red, black, and green plumage, as do many of the feral birds on Kauai — but though these birds look wild, they often have domestic bloodlines. Credit: Dominic Wright.