Long-term individual-based records of mountain goat mortality and terrain use in relation to avalanches in coastal Alaska during 2005-2022

Snow is a major, climate-sensitive feature of the Earth’s surface and a
catalyst of fundamentally important ecosystem processes. Understanding how
snow influences sentinel species in rapidly changing mountain ecosystems
is particularly critical. Whereas the effects of snow on food
availability, energy expenditure, and predation are well documented, we
report how avalanches exert major impacts on an ecologically significant
mountain ungulate - the coastal Alaskan mountain goat (Oreamnos
americanus). Using long-term GPS data and field observations across four
populations (421 individuals over 17 years), we show that avalanches
caused 23-65% of all mortality, depending on area. Deaths varied
seasonally and were directly linked to spatial movement patterns and
avalanche terrain use. Population-level avalanche mortality, 61% of which
comprised reproductively important prime-aged individuals, averaged 8%
annually and exceeded 22% when avalanche conditions were severe. Our
findings reveal a widespread but previously undescribed pathway by which
snow can elicit major population-level impacts and shape demographic
characteristics of slow-growing populations of mountain-adapted animals.