Long thought to be purebred, the wild bison of Santa Catalina Island in fact have a little bit of cow in them, the first DNA analysis of the animals found.
Nearly half of the 98 American bison shipped off the island in 2004 have cattle genes that were passed on through the mother. Catalina bison were believed to be purer than those on the mainland because they lived in isolation on the island since the 1920s.
"We were surprised because there's nothing cattle about them. They look like bison," said biologist Dennis Hedgecock of the University of Southern California, who co-authored the study.
The research done at USC and Texas A&M University appears in the latest issue of the journal Animal Genetics.
Scientists believe the crossbreeding occurred long before the bison were brought to Catalina Island. Hedgecock said the Catalina herd likely descended from animals on the famous Goodnight Ranch in Texas where cattle ranchers mated bison, also called buffalo, with cows to create a better beef animal. The ranch called the offspring of the union "cataloes."
Bison have roamed Catalina since 1924 when 14 head were brought in as extras for the silent film "The Vanishing American," though the movie did not include footage of the bison. The animals became a mainstay on the island and grew to a herd of 600 at one point.
Since the 1970s, the nonprofit Catalina Island Conservancy, which manages most of the island, has thinned the herd by auctioning the animals, some of which ended up in slaughterhouses. The conservancy ended the practice in 2003 and has since sent bison to Indian reservations for breeding and consumption.
Today, about 180 bison live on the island about 20 miles off the Southern California coast. The animals are a major tourist draw and throngs of visitors take Jeep and Hummer tours through the rugged interior to take a peek at the wooly beasts.
Conservancy spokeswoman Leslie Baer said there was great hope the Catalina bison would be genetically uncontaminated because they had been kept separate from domestic cattle. The conservancy plans to test every bison next year to see if any are purebred.
"We don't stand out as we thought we did," Baer said. "But we still don't really know what the rest of our herd look like."
The Catalina bison had not been genetically tested before, so the researchers took blood samples from the animals that were rounded up and sent to the Rosebud Indian Reservation in South Dakota in 2004. DNA analysis found 45 percent have a domestic cow as an ancestor. Although cattle genes were not detected in the remaining bison, scientists cannot say for sure they are not hybrids because of the limits of the DNA tests they performed.
Once on the brink of extinction, bison are often held up as a conservation success story. Of the estimated 300,000 bison in North America, the vast majority are mixed. In the United States, fewer than 5,000 bison are known to lack cattle genes, according to geneticist James Derr of Texas A&M, who co-authored the study.