Three now-dead cougars that found their way to Flathead Lake’s Wild Horse Island easily drove his herd of bighorn sheep down to as few as 35 of the Rocky Mountain’s prized ungulates.
Although this is an initial sum, it is the lowest number of sheep on the island in at least 20 years, according to Montana Fish, Wildlife and Parks.
About 130 sheep were counted at the island state park in 2019, and a few dozen were later removed by the department to help re-establish a herd in southwestern Montana.
In total, the three adult mountain lions – which have swum to the island or accessed its shores via an ice bridge in recent winters – appear to have killed some 70 of the vulnerable bighorn sheep before being killed by local wildlife officials over the past two months. .
The sheep may now have to be moved to the island which has served as the primary source of nearly 600 healthy bighorn sheep to Montana, Washington and Oregon over the past half-century.
If approved, it would be the first time in more than three decades that bighorn sheep would be transplanted to Wild Horse Island to augment the herd and maintain a healthy gene pool.
A field count estimates that there are 35 sheep left on the island.
“That’s what groups of people have seen; we haven’t done a flight (survey) yet,” said Neil Anderson, FWP regional wildlife program manager, of the more in-depth method of counting the island’s population.
The department announced last week that an adult female and two adult male lions were killed over the winter to protect park visitors and to protect bighorn sheep that were unable to escape on the island of nearly 3.4 square miles.
“I think what people don’t really realize is that Wild Horse Island has almost no escape ground for bighorn sheep,” Anderson said of the rocky, rocky areas that nimble sheep sabotage to avoid threats.
“So they’re quite vulnerable to predation,” he said. “To have that many cougars on the island, they could make quite a few of them on the sheep.”
An adult male mountain lion’s home range is typically more than 100 square miles, with a female’s being up to 60 square miles, according to the Forest Service.
Hardy in Montana, big cats primarily eat deer, but have been known to eat everything from grasshoppers to moose, according to the Montana Field Guide.
Wildlife officials plan to conduct an in-flight survey this spring to assess the damage the cougars have done to the valuable flock of sheep.
Two bighorn sheep were originally introduced to the island in 1939, having since thrived in range with limited predation and no documented disease.
A total of ten sheep have been relocated to the island over the years, most recently in 1987 when two bighorn sheep were moved there from Lincoln County, according to Montana State Parks.
Wildlife officials believe the three cougars – known as cunning and elusive creatures – swam to the island or more likely accessed its shores during recent winters atop the ice.
In 2019, Flathead Lake nearly froze for the first time since the early 1990s, although the lake waters surrounding the island may have frozen more recently for cats to access.
Wild Horse Island sits just off the western shore of Flathead Lake in the Flathead Preserve. FWP worked with the Confederated Salish and Kootenai Tribes to eradicate the big cats.
Wild Horse Island has produced some of the largest rams in the world, according to FWP.
The department typically targets an island population of 100 to 120 bighorn sheep to limit environmental impact on land, Anderson said.
He said a 2019 island survey showed around 130.
FWP removed 26 sheep last year to help re-establish a flock in the Tendoy Mountains of southwestern Montana and maintain a sustainable flock for the island.
It was around this time that sheep numbers began to decline.
“It started going down quite significantly after that,” Anderson said, also noting that there’s no evidence left to show that sheep are dying of disease. “The logical explanation is predation.”
Both the bear and the lion were documented on the island, “but what people were starting to see was that the lions were more used to some of the accommodations there,” he said of neighboring landowners.