Mountain goats compete with bighorn sheep for climate-limited resources

Looking through a telescope in the Rocky Mountains of Montana, conservationist Joel Berger and his doctoral student Forrest Hayes saw something strange. On a barren ridge a mile away, a group of mountain goats and bighorn sheep hung out around “these wet little mud patches,” Berger recalled. “It’s very unusual to see them together like this.”

The two researchers had no idea what the animals were doing and their bewilderment increased as they watched a male goat approach a group of sheep. The goat bent its head toward the sheep in an aggressive gesture, and before he could make contact, “the sheep moved away pretty quickly,” Berger said. “Goats have saber-like horns that even sheep probably know are up to no good.”

Fueled by curiosity, Berger and Hayes decided to further investigate these apparent interspecies tensions. After spending days out in the alpine cold and wind, watching mountain goats aggressively approach and chase bighorn sheep through binoculars and spotting scopes, they got their answer: the animals were competing for mineral deposits in the “mud patches” that had been made accessible, when mountain glaciers melt.

In a study describing their findings, published Monday in Frontiers of Ecology and Evolutionresearchers suggest that such interspecies conflicts may become more common with climate change affects the availability of patchy abiotic resources such as minerals, water and snow. “Most of society thinks in terms of what extreme weather does us,” says Berger, a professor at Colorado State University and a senior scientist at the Wildlife Conservation Society. “But different kinds of animals deal with it too. And the conflict may be intensifying as a result of the radical climate problems the planet is dealing with.

Conflict between animals, like conflict between humans, can take the form of “blood and guts” spilled in battle, Berger notes. But it also manifests as competition for resources, another type of conflict that drives ecological relationships. Conflict between animals of the same species is a frequently studied phenomenon, but much less is known about interspecific hostility. Berger says this lack of baseline data is particularly problematic for any researchers hoping to understand the nuances of current and future impacts of climate change on wildlife.

To begin filling in the unknowns, Berger, Hayes, and their co-author Mark Beal of Glacier National Park in Montana first exhaustively reviewed decades of research to find documented examples of conflicts between nonhuman animal species. They focused on extreme landscapes such as mountains, the Arctic and deserts – environments where resources are scarce even in the best of times and where, in many cases, climate change is already having a pronounced effect.

The researchers found about two dozen examples. These include wild horses chasing pronghorn, mule deer, and bighorn sheep away from waterholes in the American West; of a black rhino chasing gemsbok (a type of antelope) from shady spots in the Namibian desert; and of the domestic yak, a dominant takin (a large ungulate) over mineral deposits in the Himalayas of Bhutan. Not surprisingly, when limited resources are put under pressure, researchers have found that larger-bodied animals tend to win.

The bighorn sheep and the mountain goat are similar in size. But in field studies, Berger and his colleagues found that the goats almost always won. On three alpine fields – Caw Ridge in Alberta, Glacier National Park and Mount Evans in Colorado—they observed more than 120 collisions between goats and sheep in which one of the two animals was chased away by the other. These clashes were mainly over mineral lollipops, which are deposits of salts and other essential minerals that some animals use to supplement their diet. The Goats initiated every encounter and were victorious 98 percent of the time. Usually the sheep would walk away or skate away before a physical fight actually broke out. Like children fleeing a playground from an aggressive bully who approaches with raised fists, “in the case of the bighorn sheep, they didn’t actually need to be hit by the mountain goats to get the message across,” says Berger.

Rather than leading to any simple conclusion, Berger says, these findings demonstrate the complexity of trying to understand and conserve species in a changing world. Road construction projects have destroyed many low-grade minerals that mountain goats, bighorn sheep, and other species once depended on. So in some ways it is a positive development that retreating glaciers are opening up new resources and habitats. However, given that these new resources are limited and uneven, there will be winners and losers when it comes to access. In this case, goats were the clear winners, a finding that involved additional complications because mountain goats are not native to Colorado and some other states. Wildlife officials deliberately introduced them decades ago to provide a new revenue stream from the sale of hunting licenses.

The challenge for wildlife managers is to weigh the facts and decide what actions, if any, they need to take to help mitigate anthropogenic impacts—including from development, invasive species, and climate change—on the animals they want to protection. Managers could consider adding artificial salt lollies in places where they don’t exist, for example, or culling goats in areas where they have been introduced. For scientists, Berger adds, his team’s new research is a call to action to fill in the many unknowns that could help inform those decisions.

“This fascinating report should be a catalyst for an emerging area of ​​research—namely, how a changing climate drives species interactions,” said Joanna Lambert, a wildlife ecologist at the University of Colorado-Boulder, who was not involved in the new research. “There are no baselines here, and if we want to document change, we need starting points. These three biologists are doing just that.