About Mountain Caribou
INTRO and NOMENCLATURE
Under the Endangered Species Act, a distinct population segment—or DPS—is a vertebrate population or group of populations that is discrete from other populations of the species and significant in relation to the entire species (Fisheries.noaa.gov). The southern mountain caribou is an ecotype or distinct population segment (DPS)1 of boreal woodland caribou (rangifer tarandus caribou) that is adapted to the inland montane rainforests of the Pacific Northwest. Though once ranging as far south as the Salmon River in Idaho (Evans 1960), the current population of southern mountain caribou is now limited to interior British Columbia, where 15 extant sub-populations (two of the originally identified 17 have since been extirpated) are collectively estimated to number fewer than 1,200 individuals. Idaho’s caribou—known to biologists and conservation managers as the South Selkirk sub-population—could still be found in the jagged peaks and old-growth forests of northeastern Washington, northern Idaho, and northwestern Montana as recently as 2019. That is, however, until members from the last US-ranging caribou herd were airlifted to a captive breeding facility in British Columbia in January of that year, marking the official extirpation of the Idaho sub-population. While there is still hope of establishing a viable population of mountain caribou in Idaho, for now, the ‘gray ghost’ is just that: a ghost.
The British novelist L.P. Hartley once famously wrote: “The past is a foreign country; they do things differently there.” Mountain caribou also do things differently.
In contrast to the commonly thought of barren ground caribou of the Arctic—animals that migrate across vast distances and in large herds, mountain caribou migrate vertically, between different mountain elevation bands, in small groups averaging 5.7 animals (B.N. McLellan 2017). And unlike other cervids that move to lower elevations for the winter (deer or elk, for example), mountain caribou follow a unique late-season migration pattern that takes them higher in elevation: Beginning in mid-elevation (4,500 feet) cedar-hemlock forests in fall and early winter, they feed on residual summer forbs and lichen-heavy deadfall until the snowpack deepens and solidifies. At this point, they use their large, snowshoe-like hooves to climb to subalpine ridgelines (6,000 feet). With the snowpack forming an access barrier against predators, mountain caribou stay and feed in the high country for the duration of winter and early spring, subsisting exclusively on bryoria fremontii and alectoria sarmentosa—lichens commonly found on old growth Englemann spruce and subalpine fir trees. Here they remain mostly stationary until the spring warm-up triggers a downward migration that follows green-up back to the mountain summits for summer. In what is also likely a predator avoidance strategy, calving cow caribou make a second migration to the snow-covered ridgelines in early summer to give birth.
Former IDFG wildlife biologist Gregg Servheen on southern mountain caribou ecology:
Check out the current South Selkirk caribou managment plan (2018-2022) from the Selkirk Caribou International Technical Working Group.
No matter what they’re called—South Selkirk caribou, mountain caribou, or black caribou (as a few North Idaho old timers still call them)—the issues faced by present as well as extirpated animals are the same: habitat fragmentation and destruction due to resource extraction (primarily timber and mining), human development, large wildfires, ecosystem change and altered predator/prey regimes, habitat intrusion from winter recreative practices, and, perhaps most urgently of all now, climate change.
Since the 1980s, conservation efforts have been made by federal, state, and tribal agencies to combat these threats, including several caribou augmentation programs, the listing of the South Selkirk herd as endangered under the endangered species act, the designation of critical caribou habitat in 2016, and even periodic wolf culls by helicopter. As vigorous and unwavering as these efforts have been however, they have not been enough to keep South Selkirk mountain caribou on the landscape. Why?
Former IDFG Conservation Officer Greg Johnson discusses some of the factors behind the decline of Idaho’s caribou:
SPACE AND TIME
The decline and extirpation of Idaho’s mountain caribou is fundamentally a spatial or spatiotemporal issue. Think about it this way: mountain caribou hacked the concept of winter range as used by large herbivores and their predators. When other cervids go down, drawing their predators with them, caribou go upslope and ensconce themselves in a nutrient-poor yet predator-free vacuum. The tradeoff works and has worked for millennia: for 4 to 6 months out of the year, mountain caribou are unlikely to experience predation. For this reason, as well as for other limiting environmental factors, cow caribou have a low birth rate (only one calf per year) compared to deer, elk, or moose. The special ingredient that sustains them during the long months in herbivore outer space—the Arrakean spice melange, as it were, that mountain caribou alone have the tech to mine (snowshoes) and that allows them to subsist where others cannot—is a mixture of the two arboreal hair lichens mentioned above: bryoria fremontii and alectoria sarmentosa. Lichens are a low energy food source. Caribou must consume approximately 40g per kilogram of body weight in the winter, which, for a 400-pound bull caribou, equates to 16 pounds of lichen per day (Rominger et al., 1996). In addition, lichens are very slow growing, and their light weight means they are often blown away by wind events. As a result, the only place where lichens can be found in heavy, mountain caribou-sustaining loads are the limbs of old growth timber, into which caribou lift themselves using the deep snowpack.
The spatiotemporal recipe for mountain caribou existence is space away from other cervids and their predators—deep snowpack on subalpine ridgelines—plus the temporal dimension necessitated by old growth stands and their heavy lichen loads. A commitment to mountain caribou conservation, therefore, requires an acute sensitivity to these unique spatial and temporal dimensions and the ways in which they distinguish the worlds of mountain caribou from those of other cervids, as well as humans. Caribou time, as we’ve come to think of it, is slow or dilated relative to our own; it unfolds beyond the scale of forests grown for board feet of lumber. And caribou space, in contrast to the generalist spatialities of other, highly adaptable cervids that occupy wide and expanding areas of North America, is fragile and specific. Being contingent upon factors such as deep snowpack, old growth timber, and heavy lichen loads, mountain caribou are the time-spaces they inhabit. Without them, they vanish.
In short, mountain caribou survival requires more space and more time than we’ve been able to provide or imagine.