Mountain goats and the costs of living dangerously
April 30, 2024
Snow avalanches transform landscapes and impact alpine species. 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 show that mortality from avalanches represents a widespread but previously undescribed pathway by which snow can influence populations of slow-growing mountain-adapted animals.
(Kevin White, UVic geography PhD student supervised by Dr.Chris Darimont)
Drawing upon field data collected from four populations in coastal Alaska over a 17-year period, a recent study published in Communications Biology revealed the importance of avalanches in driving population dynamics of mountain goats – an iconic species of North American mountain cultures and landscapes.
“Avalanches transform mountain landscapes in major ways that can be both beneficial and deleterious,” said wildlife ecologist and lead author Kevin White of the University of Alaska Southeast 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 a study of unprecedented scope.
“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 as ‘a climbing bearded beast the color of winter’, mountain goats, a species of alpine ungulate comprising 32 species across 70 countries, are highly specialized for alpine life but survival requires negotiating precarious trade-offs. The ever-present risk of wolves and other large carnivores compel animals to inhabit steep, rugged terrain to minimize the risk of predation. However, utilizing predator-free cliffs exposes animals to slopes that regularly experience avalanches.
While dangerous, avalanches may also provide sustenance when slides expose vegetation, and in spring, when early-emerging “green waves” of nutritious forage appear in avalanche chutes recently swept clean of snow. Balancing of risk and reward however is tricky because avalanche risk can be largely imperceptible with the unstable layers that trigger slides being buried deep within the snowpack.
The implications of avalanche mortalities for often small, isolated mountain goat populations can be profound. By intensive monitoring of radio-marked animals and detailed field examinations of mortality events, researchers determined that over 1/3 of all deaths were caused by avalanches, occurring across nine months of the year. And, unlike other causes of death such as predation and malnutrition that selectively remove immature and old animals from the population, avalanches were found to kill animals at random. As a result, avalanche mortalities included a significant fraction of prime-aged mountain goats of high reproductive value.
An ice age relic of modern-day Pleistocene landscapes, mountain goats are sentinels of change in alpine ecosystems and particularly sensitive to shifts in weather and climate. How climate change is likely to alter the prevalence of avalanches, and their influence 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. How these dynamics play out in a future marked by climate change across the diverse range of mountain goats, and other alpine species, will have important implications for future viability and resilience.
Citation:
White, K. S., E. Hood, G. J. Wolken, E. H. Peitzsch, Y. Bühler, K. Wikstrom Jones, and C. T. Darimont. 2024. Snow avalanches are a primary climate-linked driver of mountain ungulate populations. Communications Biology. DOI : 10.1038/s42003-024-06073-0