How Killing Moose Can Save Caribou

Conservation often requires difficult decisions

EA1F4W 2.jpg
Caribou herd mountain crossing in Alaska Range. Tim Plowden / Alamy

In the contiguous United States, the iconic caribou with its branching antlers has become so rare that it’s been dubbed the “gray ghost.”

Some of the larger herds of these moose-like ungulates make the longest land migrations of any mammal, trekking across frozen ice sheets in the north of Canada. Others lead comparatively sedentary lives in the Boreal Forest, the mountains of Canada and Alaska. A handful still roam across Idaho and Washington State. But no matter where they are, they’re considered endangered. 

“Woodland caribou are probably North America’s biggest terrestrial conservation challenge,” says Robert Serrouya, a researcher at the Alberta Biodiversity Monitoring Institute and the lead author of a study published today in PeerJ. “They’re naturally rare, they cover a huge area, and their habitat needs conflict with industry, with forestry, oil and gas.”

While they aren’t necessarily a keystone species, protecting caribou means protecting old growth forests that provide habitat for countless other species,  Serrouya says. Unlike moose, which prefer glades, the  caribou  Serrouya studies live in snow-covered old-growth forests in southern British Columbia. Over the last few decades, their populations have been decimated by the cascading effects of ecosystem change, including habitat loss, climate change and an increase in wolves.

Many of these problems, it turns out, can be traced back to the caribou’s larger and more invasive cousin: the moose. Both species overlap in Canada and Alaska, where they struggle and compete to survive over vast swathes of frozen wasteland. Now, scientists are suggesting that we kill one to save the other.

How Killing Moose Can Save Caribou
Mountain caribou in British Columbia, Canada. Robert Serrouya

The problem starts with logging. In swaths of mountainous forest in southern British Columbia, loggers have long destroyed old growth trees that harbor the tree lichen woodland caribou subsist on. Logging has also opened up new habitat for moose, which historically have only lived in the area in small numbers. Once the invading moose move in, they feed on shrubs and young saplings that pop up in the clear cut areas. 

Hot on the heels of the moose are the wolves and cougars that prey on them. These plentiful wolves mostly feed on the larger numbers of moose in the area, but they also end up killing more caribou as the occasional bycatch. As a result, some caribou—known as reindeer in Europe and during Christmas—are on a fast track to extinction.

“You could protect the habitat and stop all logging and [caribou] would still go extinct,”  Serrouya says. He adds that increased forest fires due to climate change and other factors are also opening up more moose-friendly habitat.

In the past, neighboring Alberta has killed off wolves by poisoning or shooting them by helicopter in order to stabilize its Little Smoky caribou herd. It seems that effort has paid off: After officials killed off 841 wolves over seven years (as well as many moose), the Little Smoky herd appears to be on the road to recovery. However, this solution is naturally controversial, and other research says it provides only a short-term solution in an area heavily impacted by habitat loss.

In 2003, the British Columbia provincial government introduced a potentially more long-term solution when it increased its quotas for how many moose hunters could harvest, particularly females. The idea was that if hunters shot more moose, fewer wolves would hang around the area, and the caribou would suffer less from predation. 

 Serrouya and his colleagues jumped on the opportunity to track the effort. They placed radio collars placed on more than 50 wolves, 60 moose and about 300 caribou from the Columbia North herd from 1992 to 2014 in a 2,500 square mile area in the Cariboo and Columbia mountain ranges of B.C.

For years, they tracked data on where the animals were and how long they survived. They found moose were hunted down from about 1,650 animals to 300, and wolves were two to three times more likely to disperse more than 100 miles out of the experimental area. “They were more likely to get the hell out of there,”  Serrouya says. “In other words they were short on food.”

What about the caribou? Before 2003, the researchers found, caribou in the herd were dropping by about 5 percent per year. But after the increased moose harvest was opened, the population of caribou showed an increase of 2 percent per year. Meanwhile, neighboring caribou herds not subjected to moose control continued to decline.

 Serrouya calls it a “glimmer of hope” but is careful to get too excited over the small yearly increase, which doesn’t represent a real recovery in his eyes. “They just stabilized,” he says.

John Fryxell, a biology professor at the University of Guelph in Canada who was not involved in  Serrouya’s study, points out that even decade-long conservation studies sometimes aren’t long enough to fully understand what’s going on in populations of long-lived animals like caribou. Females can live up to 17 years, and their populations are subject to other long-term natural ebbs and flows in numbers. “Those things could be going on quite independently of the treatment that you’ve executed,” he says.

Yet he doesn’t believe that to be the case in Serrouya’s research. “You can quibble about some of those issues in the study but by and large the cut and thrust of what they describe in their abstract holds water,” he says, adding that the work done by  Serrouya’s research institute is some of the best on caribou conservation. “I think they’ve done a terrific job.”

Fryxell says there is some chance that this technique could be used in Ontario, despite the fact that the region is vastly larger than the area where the moose hunt quotas were increased. But the findings can’t necessarily be extrapolated to all other ecosystems, says Vince Crichton, a retired wildlife manager who worked with moose and caribou for many years for the Manitoba provincial government. Mountainous areas are very different from flat boreal ecosystems, he says, and populations of moose and caribou coexist quite well in parts of Manitoba.

“[Manitoba] for decades has had about 3,500 woodland caribou and despite the presence of wolves, bears and moose on the landscape, they have survived to about the same number today,” he says. “One solution doesn’t fit all.” He adds that caribou find a way to keep their calves away from bears and wolves by raising them on islands in lakes in the region.

 Serrouya believes that, if there is any hope for woodland caribou, more government funding for these kinds of programs is necessary. But he also believes that conservation efforts need to be multi-pronged. For instance, he says there needs to be a reduction in logging as well as more wolf and other predator killing. Aside from moose, climate change and logging is also ushering in the expansion of white-tailed deer, which  Serrouya says should also be subjected to increased hunting.

“A single approach isn't going to work,” he says. “You’ve got to hit this complicated problem at all levels. From the habitat, from the alternative prey, the moose and deer, and from the predator perspective, you’ve got to hit all three trophic levels simultaneously.”

Fryxell says that increased focus on research and action is definitely necessary not only for caribou, but for ecosystems in general.

“Nature would be way better in our country if we pursued most problems with the kind of rigor that these guys demonstrated,” he says. 

Get the latest Science stories in your inbox.