The mountain goat is one of nature’s most skilled mountaineers. The hooved herds make their way through harsh Alpine terrain with relative ease. And they’ve been living with mountain snow since the Ice Age.
According to wildlife ecologist Kevin White, that also means that they live amid avalanche paths.
“And they would have no way of knowing that,” White said. “They can’t login to the avalanche forecasters’ website.”
White is a scientist at the University of Alaska Southeast and the University of Victoria who has been tracking mountain goats to see how they meet their end. It turns out, avalanches are a leading cause of death.
According to a new study published in the journal Communications Biology, snow slides have taken out up to 22% of the goat population in the most extreme years. The research, led by White and collaborators from the University of Alaska and institutions in Montana and Switzerland, shows the scale of that mortality for the first time.
Scientists know a lot about goats’ relationship with snow. Heavy snowfall can bury food or make it more difficult for goats to move around, which can have a negative effect on survival.
But the role of avalanches has always been unclear, in part because a lot of mountain goat research is conducted in the summer, and in part because avalanche paths are remote and hard to access.
“Avalanche shoots are often a tangle of alders and Devil’s Club and salmonberry and difficult hiking to get to those sites,” White said.
White spent nearly 20 years trekking to these locations to do detective work on goat deaths, first with the Alaska Department of Fish and Game and later as a researcher who processed that data with funding from the Alaska Climate Adaptation Science Center.
He spent countless hours hovering above mountainsides in helicopters and small planes, where he first targeted goats from a distance with tranquilizers before fitting them with a GPS collar.
White collared 421 goats in Klukwan, Lynn Canal, Baranof Island and Cleveland Peninsula. Then, he waited for them to die.
Some caught disease. Some couldn’t get enough food. Some were caught by predators. A lot of those deaths were the youngest and the oldest, the most vulnerable in the population.
“But in the case of avalanches, it’s essentially selecting individuals out of the population at random,” White said.
Meaning avalanches can take out goats that are in the prime of their lives, including females who are the perfect age for reproduction. That can be a tough loss for local populations.
According to University of Alaska Southeast snow scientist Eran Hood, a co-author on the study, the new research also revealed a surprising coincidence. Avalanche-prone slopes are usually between 30 and 45 degrees — shallow enough for snow to accumulate, but steep enough for gravity to eventually pull it down.
“Well it turns out that the most common slope angle for mountain goat habitat is in the forty degree range,” Hood said. “So basically, the range of terrain where they like to hang out is right in the center of the most common slope angle for avalanches.”
If goats are risking their lives by spending time in avalanche terrain, the researchers believe there must be an evolutionary trade-off that offsets the enormous loss of life. Figuring out what, precisely, it is will require more research.
Avoiding predators who can’t make it up that high in the mountains is one possibility. Another is that snow slides unbury the food.
“Those slopes may green up sooner in the spring. And the first flush of green vegetation has really high nutritional quality,” White said. “In some areas appears to coincide with when female mountain goats are giving birth to their kids, which requires a lot of energy.”
On average, avalanches caused 8% of annual mountain goat deaths. In some years, they caused none. And in the most extreme years, in the most extreme locations, they caused 22% of deaths in the population.
Avalanche risk varies a lot from year to year, Hood said. So it’s important for wildlife managers to keep that in mind when setting annual hunting limits.
“If you knew in a winter that 22% of the population got taken out by avalanches, you should certainly be considering that in decisions you make with regard to harvest,” he said.
And as climate-sensitive mountain goats adapt to rapidly changing high mountain conditions, with more temperature variability and changing snow patterns, their relationship with avalanches may continue to change too.
