Bighorn Sheep Went Extinct on an Island Before Being Reintroduced

The bighorn sheep went extinct on Tiburón Island off the coast of Sonora, Mexico sometime between the 6th and 19th centuries, a new DNA analysis suggests.

The report is surprising because bighorn sheep were not thought to have lived on Tiburón Island until the mid-1970s when they were introduced there by humans as part of a conservation effort.

Writing in the journal PLOS One, a research team led by conservation biologists at University of California, Riverside reports that the iconic bighorn sheep once lived on the small and largely uninhabited island up to 1,600 years ago.

The discovery came after researchers found a mat of urine and dung in a mountain cave on the island's rugged eastern side.

Study co-author Jim Mead, a paleontologist at East Tennessee State University determined that the excrement belonged to bighorn sheep by comparing it to an extensive catalog of dung from both living and extinct herbivores. A subsequent DNA analysis confirmed the suspicions that the dung belonged to bighorn sheep.

Puzzled because bighorn sheep were not known to live on the island until recently, the researchers conducted another DNA test to determine that the dung samples were not identical to dung of modern bighorn populations living on Tiburón.

The researchers say that the find could have implications for future conservation efforts as well as raises questions about how to define the new population of bighorn sheep on Tiburón.

"With extended biological baselines, such as the knowledge that the Tiburón bighorn sheep went extinct before, it is possible to refine conservation targets," said lead study author Benjamin Wilder, a Ph.D. graduate student in UC Riverside's Department of Botany and Plant Sciences. "Given the cultural and conservation significance of the Tiburón bighorn, actions can be taken to avoid their past fate."