Two competing species: mountain goat v. bighorn sheep
Summit Daily News
Populations of bighorn sheep are lean compared to mountain goats in Summit County. This unbalance is causing local experts to investigate how to stabilize their numbers.
“Mountain goats are much more of a generalist species, which aids in their survival,” said Colorado Parks and Wildlife terrestrial biologist Janet George. “Bighorn sheep are a less hearty species so their populations reflect that.”
Mountain goat species are a heartier species than bighorn sheep, able to survive on a wider range of plants in Summit County while Rocky Mountain sheep are more susceptible to disease, George said.
Wildlife managers such as Sean Shepherd from Colorado Parks and Wildlife are managing the populations of the two species based off many factors that may be to blame.
The population of bighorn sheep in Summit County is not clearly defined by local wildlife managers, but the population of mountain goat falls somewhere between 300-400.
“Bighorn sheep winter in areas that are rugged and hard to reach, which make them hard to track,” Shepherd said. “We estimate populations of mountain goats to be in the low hundreds, while we’ve counted 50 or so sheep in the Montezuma area and a population in Eagles Nest area.”
Tracking and collaring of the bighorn sheep in Summit County this autumn will produce a more conclusive population size, Shepherd said.
What is apparent is the higher prevalence of mountain goats in the area compared to bighorn sheep. Though neither mammals are considered endangered, the population of the bighorn sheep is “out of whack,” Shepherd said.
Efforts to manage the population have not been successful in increasing the population of Rocky Mountain sheep in Summit County.
“Bighorn sheep have not responded well to our management efforts, and that’s due to a loss of habitat and disease,” Shepherd said.
Bighorn sheep populations are especially low in the Gore Range, which runs some 60 miles through western Grand and Summit County, George said.
“That may be a reflection of respiratory disease among bighorn sheep,” George said. “Though they are more susceptible to disease, we are unsure what infects them.”
Why mountain goats may be to blame
Theories suggest mountain goat populations assert their aggressive nature and move in on herds of bighorn sheep pushing them away from quality forage and habitat.
Domestic goats and sheep transmit respiratory disease and fatal pneumonia in bighorn sheep, shown by evidence gathered in the Rocky Mountain Region by the US Department of Agriculture in 2008.
The diseases that plague them is the main reason for the small population compared to mountain goats, Shepherd said.
“Bighorn sheep just seem more susceptible to diseases compared to mountain goats,” Shepherd said. “We don’t know why, but mountain goats are a more hardy species.”
Mountain goats are also a more aggressive species, Shepherd said.
“They assert their dominance regularly where bighorn sheep are less prone to do so,” he said.
Mountain goats have a very distinguished hierarchy among their group and maintain it by dominance interactions, Shepherd said.
The difference in behaviors in mountain goat and bighorn sheep can also be illustrated by their horns.
Mountain goats have sharp horns that point forward because they use them to maintain dominance. Bighorn sheep are a less-assertive mammal – their horns are curved and rarely used outside mating season.
So have the goats been bullying sheep?
“We have not seen this happen in Summit County, but it is reasonable to assume that mountain goats may assert their dominance when they come in contact with bighorn sheep,” Shepherd said.
Colorado Parks and Wildlife have transplanted bighorn sheep in areas with little human activity, near Climax Mine in attempts to bolster the population.
Different vaccines for the diseases that plague them, have also been used by wildlife managers.
Hunting has also been modified to level out the populations of the two species.
“We’ve limited hunting for bighorn sheep,” Shepherd said. “On the other hand, we’ve made available five licenses to hunters and four seasons for mountain goat.”
Beginning in September, Colorado Parks and Wildlife biologists will begin counts by ground and helicopter to identify the numbers of bighorn sheep and collar them with GPS tracking to see where they are wintering.
“If sheep are coming in contact with mountain goats during wintering months, that may be the reason they have not responded well to management,” Shepherd said. “The only places we have possible interaction between the species is up around Montezuma.”
After counting and collaring bighorn sheep, their wintering and breeding will be monitored to determine if they are reproducing at a rate high enough to sustain their population.
“We’ll be looking to see if the population or health goes down in these areas that interaction may occur,” Shepherd said. “Early indicators have to do with the next generations of mammals.”
The goal of management is to reach a point where both species’ populations are sustainable without management, Shepherd said.
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