The charismatic mountain mammals face a list of threats: climate change, development, outdoor recreation pressure and accidental killing by trapping. Can they survive?
Wolverines epitomize the paradox of a wide-ranging species
that, compared to other carnivorous wildlife, exists in low densities and
scarcity of numbers. Across all of the American West in the Lower 48, there is
guestimated to be only a few hundred wolverines left.
In 2002, the Wildlife Conservation Society began a wolverine
collaring project in the Tetons, and found the range fully occupied. By
capacity, that translated into just four adults—two males and two females—inhabiting
the entire span of the Tetons. The territories of those animals also
encompassed Grand Teton National Park and parts of the adjacent national forests.
Over the course of the next few years, one of these pairs
produced two female kits, who were captured and collared in a den on the west
side of the Tetons.
This den represents the southernmost natural reproduction
documented in the US, making the Tetons a landmark for those in the wolverine
world. At the time, we believed that the Tetons represented the latest frontier
in a decades-long recolonization following the extirpation of wolverines from all
of the Rockies in the early 20th century.
When one of the Teton kits traveled to the Wind River Range
100 miles distant and established a territory there, and when a young male from
the project area traveled hundreds of miles more to Colorado, we believed we were seeing the ongoing re-expansion
of wolverines across their historic range – a rare, hopeful story in the annals
of 21st century wildlife conservation.
But survival for a rare species in landscapes being
fragmented by ever-more human uses and by climate change literally melting away
the range of habitat and seasonal presence—snowpack—beneath their feet, that
brief euphoria proved to be tenuous at best.
In 2014, an entity called the Idaho Wolverine and Winter
Recreation Project set up live traps at the same Teton locations where the
Wildlife Conservation Society had trapped. Researchers with the Winter
Recreation Project caught just a single male, known as “Jed” for his capture location
in the Jedidiah Smith Wilderness.
Jed had first been captured by WCS in 2002, making him at
least 14 years old. In 2015, the Winter Recreation Project again failed to
capture any additional Teton wolverines. Jed was alone in the range, it seemed,
patrolling a 355 square-mile territory—actually a small but respectable home
range for an adult male.
Yet without a mate, his solitary presence meant that the
Tetons had gone from being a reproductive node for a possible wolverine meta-population
in the Greater Yellowstone Ecosystem to being effectively empty.
In the following last couple of years, the Forest Service
set up camera traps in search of wolverines and lynx. Jed failed to appear on
those cameras. Two other detections of wolverines yielded no evidence of a
long-term reproductive population in the range, as none of the animals were photographed
more than once.
"Without a mate, Jed's solitary presence meant that the Tetons had gone from being a reproductive node for a possible wolverine meta-population in the Greater Yellowstone Ecosystem to being effectively empty."
The disappearance of wolverines from the Tetons represents a
mystery. The potential explanations for that disappearance hint at three
cautionary stories that we might tell about wildlife in the era of human-caused
climate change.
Wolverines are climate-sensitive. They are tied to cold and
snowy landscapes in many ways. South of 54 degrees latitude, they invariably
den in spring snow. This is likely only one of many ways in which wolverines strategically
use a cold, snowy landscape, but it’s the one that’s received the most
attention over the past several years, since it’s tied to the petition to list
wolverines under the Endangered Species Act.
Climate modeling suggests that late spring snow will decline
by up to 60% in the US northern Rockies over the coming century, potentially
knocking wolverines out of their strongholds in the Lower 48. As the southernmost
reproductive population node in the Lower 48, the Tetons may be experiencing warming
effects that make the range less hospitable to wolverines than it has been in
the past. The narrative here is about wildlife vulnerable to climate change, a
force that is currently largely outside of our control, but that still demands
our attention.
Map of present suitable wolverine habitat versus likely outlook in the 21st century as warming average temperatures reduce mountain snowpack. It means providing refugia where wolverines are free from disturbance will be even more important. Map use courtesy American Museum of Natural History
A second possible issue is recreation. Despite claims that
wolverines are highly sensitive to the presence of people, there’s no
conclusive evidence yet that this is true. But there’s also no evidence that it
isn’t. Snowmobilers and backcountry skiers are reaching ever remote corners of
Greater Yellowstone and like a lot of things in times of budget cuts hampering
official government research, absence of scientific evidence does not equate to
absence of impact.
The Winter Recreation Project, which started with the
explicit goal of measuring snowmobiling and skiing impacts on denning female
wolverines is currently in the data analysis phase, so we don’t yet have
results from the one project that may provide some insight on this question.
"This seems simple and straightforward, but humans are notoriously slippery and self-interested, including recreationists purporting to be advocates of wildlife conservation, so human management may prove almost as difficult as halting climate change."
Understanding the impacts of recreation, in the face of
growing pressure from a widening number of users, can help create a more
informed narrative to how to better manage human behavior in order to preserve wildlife
sensitive to disturbance. This seems simple and straightforward, but humans are notoriously slippery and self-interested, including recreationists purporting to be advocates of wildlife conservation, so human management may prove almost as difficult as halting climate change.
Finally, it’s possible the absence of wolverines from the
Tetons may be part of a natural cycle of recolonization and local extinction
that characterizes meta-populations.
This we know: it can take the loss of a single wolverine—half a mating
pair—to effectively extirpate the species from a mountain range. Woverines are
vulnerable to traps set for wolves and other animals. Average temperatures are
rising and snowpacks that provided terrain conducive for wolverines is in
decline. Along with it, population
projections suggest more people entering the backcountry in coming decades.
With islands of habitat (mountain ranges) interspersed among
wide swaths of non-habitat (lowland), juvenile wolverines must cross
inhospitable landscapes to reach places that can support them. The chances of
any mountain range receiving both a male and a female wolverine in a given
stretch of time probably varies with proximity to the nearest occupied mountain
range, development in the intervening lowlands, and natural obstacles to
travel.
We have almost no concept of how connectivity functions,
what the timelines are for these local extinction and recolonization dynamics,
or how human land use affects both wolverine behavior and connectivity. These
are questions that bear further, and careful, investigation.
"We’re still caught up in our traditional patterns of describing individual threats to any given species. It’s time we learned to think and talk about all of these potential threats at once, and to face the reality of the need for action in multiple arenas."
What can we hope for? A strategy devoted to emphasizing
habitat which focuses on the natural cycles of wolverine expansion and
connectivity. Were this to happen, there might be room for optimism because
such a strategy is based on the premise that given enough time and the right management
of the landscape, wolverines will persist.
And then there’s a fourth possibility: that all of the
factors, above, are congealing to create exponentially daunting obstacles to the
survival of wolverines in Greater Yellowstone, that in an ecosystem touted globally
for having all of its original mammalian parts, Gulo gulo could be the first to
go, a victim of wildness being frayed.
Development, recreation, and climate change represent a toxic
mix for many species. Cumulatively, they may be too much for wolverines and for
other wildlife.
We’re still caught up in our traditional patterns of
describing individual threats to any given species. It’s time we learned to
think and talk about all of these potential threats at once, and to face the
reality of the need for action in multiple arenas, if we truly want to preserve
all of the wildlife that makes Greater Yellowstone so unique.
EDITOR’S NOTE: Mountain Journal columnist Rebecca Watters penned this piece on wolverines just before she boarded a flight to continue her wolverine and snow leopard conservation work in Mongolia. Executive director of The Wolverine Foundation, Watters divides her time between Asia and Bozeman. PS: below, the author recently put her hand next to paw prints of a snow leopard high on the Asian steppe.
And, a few days later, this photo, below, shared by Rebecca Watters on social media in October 2017, replete with this observation: "a seventeen-year dream fulfilled":
About Rebecca Watters
Rebecca Watters is a wildlife biologist, research associate with the Northern Rockies Conservation Cooperative in Jackson, Wyoming and executive director of The Wolverine Foundation based in Bozeman, Montana.
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