Study: Many Mountain Goats Die in Avalanches

Details

Category: Local News

Created on Wednesday, 15 May 2024 14:31

By GARLAND KENNEDY
Sentinel Staff Writer
    Living amid craggy peaks and remnant glaciers, Southeast Alaska mountain goats survive in variable conditions, often dealing with heavy snowfall and extreme cold. But a new study published and written by an Alaskan wildlife ecologist shows that many goats die in avalanches.
    Kevin White, who worked with the Alaska Department of Fish and Game before continuing his studies at the University of Alaska Southeast and University of Victoria, has concluded over a 17-year project, using data from 421 collared goats, that between 23 and 65 percent of them died in avalanches, depending on conditions in a given year.

An adult male mountain goat is pictured during late winter, near the Juneau Icefield. (Photo by Kevin White)

    “On average, about a third of all mortalities were comprised of avalanches,” White told the Sentinel by phone last week, “but it varies spatially, so it depends on the area under consideration. And so Baranof Island had the highest fraction of all mortalities being comprised by avalanches, but part of the reason why that occurs, it’s not just that Baranof is a place that’s extraordinarily steep and rugged… but it also gets a lot of snow. So it’s prone to avalanches,” he said.
    “But the other important consideration with respect to Baranof is in the wintertime there’s really very limited chance of predation like there is on the mainland when there’s wolf packs,” he said.
    White co-published the study, “Snow avalanches are a primary climate-linked driver of snow ungulate populations” along with Eran Hood, Gabriel Wolken, Erich Peitzsch, Yves Bühler, Katreen Wikstrom Jones and Chris T. Darimont in the scientific publication Nature on April 29.
    A future line of questioning, White noted, will revolve around the impact of climate change on snowpack, and how warmer conditions in Southeast impact avalanche risk and goat mortality.
    “That is sort of one relevant factor about identifying this process that is influenced by climate and it’s something that one of our colleagues, Gabe Wolken (at UAF), has been working on his own trying to learn, run some simulations to understand how characteristics and distribution of avalanches might change going into the future given climate change projections,” White said, “but at this stage, we don’t really have specific insights.”
    Goats, with their uncanny ability to traverse vertical terrain, tend to inhabit mountaintops far above the tree line, and excel in that alpine ecosystem.
    “They’re a species that just feels like they’re straight out of the last Ice Age,  and they really are, actually; they still are living in Ice Age environments, like what’s remaining of remnant glaciers,” White said.
    He first came to Alaska in 1996 for moose research in the Talkeetnas, but in 2001 moved to Juneau to work with Fish and Game. Since 2022, he’s been with both the University of Alaska Southeast and British Columbia’s University of Victoria, where he’s working on his dissertation. He lives in Haines.
    The study delves into “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.”
    He studied collared goats in Lynn Canal near Klukwan, on Baranof Island and on the Cleveland Peninsula, with the highest rate of avalanche fatality occurring on Baranof. Of the 51 studied goats that died near Sitka, 33 perished in snow avalanches, the paper states. Of all goats studied across the region, 36 percent died in avalanches. While predators will often target the old, young or infirm, White noted, avalanches kill indiscriminately, often taking out mature adults.
    “Avalanches are taking out prime-aged animals that are the most important ones for popular population productivity,” he said. “That’s a pretty important take-home point.”
    Avalanche deaths peaked in periods of unstable snow – in October and November as snowpack first accumulates, and in April and May as it melts.
    Due to the nature of falling in an avalanche, the study says, this manner of death presents a “wicked problem” to goats.
    “While we didn’t explicitly test whether mountain goats select specific terrain types to avoid avalanches during risky periods, the complex and dynamic physical interactions that create avalanche vulnerability are likely difficult to detect among wildlife, minimizing opportunity for development of behavioral strategies to avoid avalanche hazards in areas and periods of snowpack instability… Avalanches may represent a ‘wicked problem’ – that is, there are limited opportunities for trial-and-error learning due to the catastrophic outcomes that follow initial exposure.”
    However, the high rate of avalanche deaths around Sitka presents an incomplete picture.
    “On Baranof, there’s really less ways that mountain goats can die. And so as a consequence of that… a higher fraction (of deaths) is comprised of avalanches, but overall survival of mountain goats on Baranof Island is generally higher than other mainland populations, because there’s reduced predation pressure,” he said. By the time snow begins to push some goats to lower elevations where they would make easier prey the bears have typically denned up for the winter.
    Goats are an indicator species for high country ecosystems, White said, and research has often not focused on them.
    “I’ve always been really interested in learning about mountain environments, just from a kind of a broader natural history and ecological perspective,” White said. “So mountain goats are just an iconic species. They’re sort of sentinels of health and function of alpine ecosystems, and so it’s really just a fascinating species to work on and provides opportunities to learn more about our alpine ecosystems.”
    Goat country ranges from the Northern Rockies through Canada and into Alaska. Because the animals inhabit craggy areas difficult and dangerous for most humans to access, goats “have always been among the least studied large mammals in North America. So our knowledge of the species has been much more limited compared to species that are easier to study such as deer, moose, for example, or caribou.”
    While there have been goat studies in Alaska previously, he said, these have not had the duration of his 17-year project, though he noted one larger study in the Canadian Rockies.
    His study began with an interest in how the expansion of the Blue Lake dam would impact mountain goats’ winter range, and on the effect from the proposed hydroelectric project on Takatz Lake, which would cut through goat country.
    Fish and Game collected monitoring data for the project, and the City of Sitka, U.S. Forest Service and Bureau of Land Management cooperated with the study.
    Avalanche mortality varies widely year to year, White said, with up to a third of a goat population dying that way in a year. But in some years, only a handful of goats die in avalanches.
    Helicopter surveys conducted annually indicate there’s a sizable population of goats on Baranof Island, ADF&G wildlife biologist Steve Bethune told the Sentinel, though the number fluctuates over the years. Since White left the department, Bethune noted, no additional goats have been collared on the island, and now fewer than 20 goats are tagged and tracked.
    Sitka’s population peaked at around 1,900 animals in 2019, Bethune noted, and while numbers have fallen a bit since then, the margins of error for the surveys overlap. High winds and cold weather that formed ice sheets resembling goats hampered the 2023 survey, leading Bethune to have a low degree of confidence in its conclusion that there were 1,250 goats on Baranof, especially since hunters last year reported finding goats in their usual numbers. He plans to fly again this fall.
    Last year hunters tagged 29 animals in Game Management Unit 4 – in line with recent years.
    Though the study didn’t originally intend to analyze avalanches or avalanche mortality on goats, White said, his interest in the impacts of snow on mountain ungulates drove the work.
    “We’re focused on understanding how snow influences wildlife and our traditional ecological understanding is focused on snow being a process that... impedes movement and increased energetic costs, and also buries food… What we’ve identified is more how snow can act as a purely physical process sliding down the hillside and how that is an important other dimension on how snow influences wildlife populations,” White said, “and it may be quite prevalent across mountain ungulate species… We’re now able to have a better understanding of how it might impact populations.”