Tue Apr 21, 2015 5:51am BST

Montana has closed the hunting season on a wild herd of bighorn sheep, with pneumonia suspected of killing dozens of the animals whose seasonal mating rituals attract scores of wildlife watchers.

The emergency closure came after the disease-related deaths of more than 90 of the animals from a herd in northwestern Montana, where just 18 bighorns were counted earlier this month during a helicopter survey by state wildlife biologists. That is the lowest count since the herd was reintroduced to the area in 1979, they said in a statement.

The step marks the second such hunting closure by the Montana Fish and Wildlife Commission, with a similar move on March 23 for a herd near Yellowstone National Park, also due to fears over pneumonia.

Such pneumonia outbreaks have been linked to contact between wild sheep and domestic ones that graze on public ground and private land across the Rocky Mountain West.

More than 1 million bighorns once roamed the region but their numbers had fallen to just tens of thousands in the first decades of the 20th century because of unregulated hunting and disease, according to the Wild Sheep Foundation.

Wildlife managers in Montana and other Western states have renewed efforts in recent years to reintroduce wild sheep in areas where disease and historical over-hunting pushed them close to extinction.

Bighorns are prized for their elaborately curled horns and for mating rituals in which rival rams crash horns after running at each other at speeds up to 40 miles (65 kilometers) per hour.