Mountain goats and the costs of living dangerously

Mountain wildlife and the costs of living dangerously

Mountain goats use steep, exposed terrain to avoid carnivores such as wolves, but new research reveals a significant cost of this behavior: exposure to snow avalanches.

Findings from a long-term study by researchers at the University of Alaska Fairbanks and the University of Alaska Southeast with partners in Canada and Switzerland show that death from avalanches represents a widespread but previously undescribed pathway by which snow can influence populations of slow-growing mountain-adapted animals.

Using field data collected from four populations in coastal Alaska over 17 years, a study published in Communications Biologyrevealed the importance of avalanches in driving population dynamics of mountain goats, an iconic species in North American mountain cultures and landscapes.

The wide-ranging study was funded by the Alaska Climate Adaptation Science Center, hosted by UAF, as part of its mission to understand climate impacts on Alaska's land, water, animals and people.

"Avalanches transform mountain landscapes in major ways that can be both beneficial and deleterious," said wildlife ecologist and lead author Kevin White of UAS and University of Victoria. "Our study provides the first detailed evidence of the latter, namely the striking impact avalanches can have on mountain wildlife population demography, with up to 22% of individuals killed by avalanches in a single year."

The multidisciplinary team of wildlife and snow scientists from the US, Canada and Switzerland combined long-term field data from over 400 satellite-tagged mountain goats with innovative avalanche hazard modeling techniques to conduct the study.

"This project offered a unique opportunity to explore how the physical process of avalanching snow influences wildlife populations, adding to our existing ecologically oriented understanding of snow-wildlife relationships," said Eran Hood, a professor of environmental science at the University of Alaska Southeast and co-author of the study.

Famously described by author Douglas Chadwick as 'a climbing bearded beast the color of winter,' mountain goats are alpine ungulates comprising 32 species across 70 countries. They are highly specialized for alpine life, but their survival requires negotiating precarious trade-offs.

The ever-present risk of wolves and other large carnivores compels them to inhabit steep, rugged terrain to minimize the risk of predation. However, the predator-free cliffs expose animals to slopes that regularly experience avalanches.

While dangerous, avalanches may also provide access to sustenance. Slides expose vegetation in winter and later in spring, when early-emerging "green waves" of nutritious forage appear in avalanche chutes recently swept clean of snow.

However, balancing risk and reward is tricky. Avalanche risk can be hard to detect, with the unstable layers that trigger slides being buried deep within the snowpack.

The implications of avalanche mortalities for small, isolated mountain goat populations can be profound.

By monitoring radio-marked animals and examining mortality events, researchers determined that more than a third of all mountain goat deaths were caused by avalanches occurring across nine months of the year.

Unlike predation and malnutrition, which selectively remove immature and old animals from the population, avalanches kill animals at random. As a result, avalanche mortalities included a significant fraction of prime-aged mountain goats of high reproductive value.

How climate change is likely to alter the prevalence of avalanches and the resulting impact on the species is an important area of future research. Existing evidence suggests changes will vary geographically and track projected increases in extreme weather events. These dynamics will play out across the diverse range of mountain goats and other alpine species and have important implications for their future viability and resilience.

An ice age relic of modern-day Pleistocene landscapes, mountain goats are sentinels of change in alpine ecosystems because they are particularly sensitive to shifts in weather and climate.

ADDITIONAL CONTACTS: Kevin White, [email protected], 907-723-3226; Eran Hood, [email protected], 907-796-6244

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