Nearly one third of the park's buffalo herd was killed last year by government agencies over concerns the bison could transmit the disease brucellosis to commercial herds of cattle grazing in the park. Brucellosis is a bacterial disease that causes weight loss and abortion of calves.

Alternative solutions to culling the herd could include buying grazing rights from cattle ranchers in a few areas around the park or testing all cattle within a special zone, said Marm Kilpatrick, a professor at the University of California, Santa Cruz, lead author of a new study of park bison in Montana and Wyoming.

A risk analysis conducted by Kilpatrick's team shows the risk of transmitting brucellosis to cattle is very low in most years and periodically high only in some areas.

"To me, the most interesting result of the study was that in a number of years, the model predicts there will be no risk of transmission at all," Kilpatrick said.