Woodland Caribou: A Conservation Dilemma

By: Peter Zager, L. Scott Mills, Wayne Wakkinen, and David Tallmon

At the time of European settlement of North America, caribou (Rangifer tarandus) were found over most of Canada and Alaska. Woodland caribou (R. t. caribou) extended south to 42 degrees N, and were found in parts of New England, New York, the Upper Great Lakes states, Montana, Idaho, and Washington. By the 1970s, woodland caribou had been eliminated from the eastern United States and most of eastern Canada, extending only to approximately 48 degrees N (Bergerud 1978). The decline extended to the west as well, and by 1980 only 25-30 animals persisted in north Idaho and northeast Washington; caribou had been extirpated elsewhere in the contiguous 48 states. This population was listed as endangered in 1984 under the Endangered Species Act (ESA). At that time, the entire woodland caribou population in the Selkirks consisted of one herd of 20-25 animals that occurred in extreme northeast Washington, northern Idaho, and the Stagleap Park area of British Columbia (B.C.). The decline in woodland caribou was attributed to various factors including:

To address woodland caribou recovery, an interagency recovery plan was developed (USFWS 1985). The plan addressed the factors in caribou decline by calling for:
1. Controlling poaching,
2. Minimizing caribou deaths due to collisions with vehicles,
3. Improving habitat quality by closing roads and allowing natural succession, and
4. Augmenting the existing Stagleap population and/or establishing a second population outside the Selkirks (USFWS 1985).

Items 1 and 2 were easily addressed, as were certain aspects of Item 3, but population augmentation was more controversial and complex. Therefore, an augmentation plan was developed and approved (Summerfield 1985a, 1985b). A total of 60 animals were transplanted from British Columbia to the Selkirk Mountains of Idaho. Twenty-four animals were released in 1987, 24 in 1988, and 12 in 1990. The release site was south of the existing resident herd. The intent was to establish a second herd in the Selkirks, thereby reducing the chances of extirpation by way of some catastrophic event eliminating the lone resident herd.

All translocated animals were fitted with mortality-sensing radio collars so they could be monitored systematically. As a result, we obtained good data relative to habitat use, movements, and causes and rates of mortality for caribou in the Selkirks. A winter helicopter census was also developed that allows us to track population size and distribution throughout the ecosystem.

Results of Translocation Efforts

Unfortunately, even a cursory look at our data and today's caribou population in the Selkirk Mountains is not encouraging. We began with 25-30 caribou in the Selkirks in the early 1980s and added 60 to the ecosystem with the augmentation, however today's population is only about 55 caribou. Furthermore, the herd that was established with the augmentation presently consists of only 13 animals. Clearly the augmentation did not catalyze the desired population response.

In response to this, a revised recovery plan called for establishing a second population via augmentation (USFWS 1993). Arguments for another transplant were similar to the first, including reduction of the chances of extirpation with several herds and the desire to place animals in all "available" habitats. The recovery plan also called for a thorough evaluation of the initial augmentation effort and current population dynamics before moving ahead. To that end, we compiled all relevant data and used them as input for population viability analysis using VORTEX and RAMAS.

The analyses shed some light on long-term, broader scale issues while confirming the obvious. They demonstrated that the population is declining, and more importantly, indicated that the simplest and most expedient way to reverse that trend is to eliminate virtually all known predator-related mortality, which accounted for at least 30% (and more likely 50%) of the total mortality. This poses a serious problem for managers, for as the state of Alaska recently discovered, controlling predator populations is a very sensitive issue.

The analyses also showed that caribou are likely to persist in the southern Selkirks for at least the next 20 years, but because of differential survival and movements, virtually all the animals will be part of the resident herd in B.C. Furthermore, the population is likely to stagnate at 40-50 animals, so the probability of persistence at 100 years is less encouraging.

These results indicate that we are not progressing toward recovery, and additional augmentation efforts are unlikely to change that unless there is a fundamental change in caribou demographic rates, specifically an increase in adult survival. Simply adding more animals may buffer the existing herds against the effects of demographic, environmental, and genetic stochasticity, but is unlikely to speed "recovery." Our modelling analyses and previous experience with augmentation indicate this approach will treat the symptoms but not the fundamental causes of caribou decline.

The Underlying Dilemma

Therein rests the underlying issue -- our best efforts to "recover" caribou in the Selkirk Mountains have not worked. It seems that we have at least two options. The first option is to rethink the spatial scale of conservation efforts and to redirect our energies and resources where the likelihood of success is higher, such as to the stronger, more viable populations in Canada. It is unlikely that caribou can survive in the Selkirks without habitat and a strong population in adjacent British Columbia. We may be wise to forge a cooperative effort with our Canadian neighbors and develop a plan to more effectively ensure caribou persistence on a larger scale. If Canadian populations are doing well, then there may be little risk in continuing to supply a "sink" population south of the U.S. border with transplants. On the other hand, if the "source" populations are marginal, we may increase the likelihood of caribou extirpation on an even larger scale by continuing translocations.

In the broader context, Griffith et al. (1989) showed that augmenting a species in peripheral habitat is unlikely to succeed. In addition, Lesica and Allendorf (1995) suggest peripheral populations isolated by recent range contraction are unlikely to be genetically differentiated, and thus are less likely to have a large degree of conservation value.

Our second option involves rethinking the temporal scale of recovery. Decision-makers, managers, and the public typically expect recovery programs to demonstrate highly visible, high-profile progress over a relatively short time frame. This is unrealistic because recovery programs are designed to reverse long-term population declines often resulting from decades of habitat loss or degradation. It is unreasonable to expect populations to respond quickly to recovery efforts that do not first consider habitat restoration that may take decades. Simply stopping or mitigating further habitat loss or degradation may not be sufficient.

Woodland caribou habitats in the U.S. have changed considerably over the last 100 years, limiting caribou distribution and population size. Caribou in southern British Columbia and northern Idaho "prefer" mature-to-old-growth forests above 1364 m elevation throughout the year (Scott and Servheen 1985, Simpson et al. 1987, Servheen and Lyon 1989). Timber harvest activities over the last 50 years and large wildfires since the turn of the century have altered the habitat mosaic dramatically and resulted in a younger-age forest. The result is that habitats in north Idaho are less extensive and less suitable for woodland caribou today than they were a few decades ago.

Habitat conditions at lower elevations, below identified caribou habitat, have also changed. Timber harvest is an economically important land use at these elevations and has resulted in extensive seral communities that provide very good habitat for expanding moose (Alces alces) and white-tailed deer (Odocoileus virginianus) populations. Predator populations, especially mountain lions (Felis concolor), have apparently responded to the abundant prey base. Consequently, although caribou are not the primary prey item, predation by mountain lions has become an important mortality factor for caribou in the Selkirk Mountains. Furthermore, woodland caribou are a classic K-selected species in that females do not breed until 2 years of age, rarely produce twins, and often calve every other year. Because of this low reproductive potential, their populations cannot tolerate high mortality.

Reversing the Trend

To reverse this downward population and habitat trend, we believe it is necessary to embark on a grand experiment including an aggressive, long-term habitat management and restoration program designed to shift the balance from seral communities to mature and old-growth communities. To be effective, this must extend beyond identified caribou habitat to include lower elevation white-tailed deer habitat. We expect that this will also shift the balance from whitetails and their predators to caribou and other species characteristic of mature forest communities.

The most obvious problem is that this will require a commitment of at least 100 years to habitat restoration before we can reasonably expect caribou to thrive in the Selkirks. It is easy to envision another large wildfire during that period that would slow the process considerably. We also question the public and agency commitment to such a long-term project.

There may also be short-term, stop-gap measures that will result in the necessary fundamental change in caribou demographic rates, increasing the likelihood of recovery. Directly reducing white-tailed deer and predator densities may have the desired effect, but not without a significant commitment. Care must also be taken to avoid the "predator control" label that such a program may attract. If such an approach were implemented, it behooves us to conduct it as part of an experiment that will provide data and insights for future recovery activities.

Broader Questions

This leads to the broader and more significant questions. Does it really matter if there are a few caribou south of an arbitrarily drawn international border? Must "recovery" occur within the 5-10 year framework typical of agency planning documents? We suspect that over the next decade or so, similar discussions will focus on lynx (Felis lynx), wolverine (Gulo gulo), fisher (Martes pennanti), and other species that reach the southern extension of their range near the U.S./Canada border. At the same time, Canadian biologists will likely discuss conservation measures for species such as spotted skunk (Spilogale spp.), gray fox (Urocyon cinereoargenteus), and eastern cottontail (Sylvilagus floridanus); all of which are common in the U.S. but reach the northern extension of their range near the U.S./Canada border. In our view, conservation efforts should be based on the biology of the species applied at much broader spatial and temporal scales than we typically use. This will require increased cooperation between Canadian and U.S biologists and political bodies.

We do not advocate turning our back on woodland caribou, but rather drawing a realistic "line in the sand," then channeling energy and resources to secure those populations and habitats necessary to ensure their future on a global scale. Political boundaries must not obstruct our vision or thinking, and time frames should be expanded to realistically address many conservation issues. With a broader perspective, conservation efforts will enjoy a much greater likelihood of success.

Literature Cited

Bergerud, A.T. 1978. Caribou. Pages 83-101 in Big game of North America: ecology and management. J.L. Schmidt and D.L. Gilbert, eds. Stackpole Books, Harrison, PA.

Griffith, B., J.M Scott, J.W. Carpenter, and C. Reed. 1989. Translocation as a species conservation tool: status and strategy. Sci. 245:477-480.

Lesica, P., and F.W. Allendorf. 1995. When are peripheral populations valuable for conservation? Cons. Biol. 9:753-760.

Scott, M.D., and G. Servheen. 1985. Caribou ecology. Job Compl. Rep., Proj. No. W-160-R-11. ID Dep. Fish and Game, Boise. 136pp.

Servheen, G., and L.J. Lyon. 1989. Habitat use by woodland caribou in the Selkirk Mountains. J. Wildl. Manage. 53:230-237.

Simpson, K., G.P. Woods, and K.B. Hebert. 1987. Movements and habitats of caribou in the mountains of southern British Columbia. B.C. Min. of Environ., Wildl. Bull. No. B-57.

Summerfield, R. 1985a. Selkirk Mountains caribou herd augmentation: a cooperative interagency plan. U.S. Dep. Agric., For. Serv., Idaho Panhandle National Forests, Coeur d'Alene.

__________. 1985b. Environmental assessment, Selkirk Mountains caribou herd augmentation. U.S. Dep. Agric., For. Serv., Idaho Panhandle National Forests, Coeur d'Alene.

U.S. Fish and Wildlife Service. 1985. Selkirk Mountain caribou management plan. U.S. Fish and Wildl. Serv., Portland, OR.

__________. 1993. Recovery plan for woodland caribou in the Selkirk Mountains. Portland, OR.

The Authors can be contacted at the following addresses:
Peter Zager, Idaho Department of Fish and Game, 1540 Warner Avenue, Lewiston, ID 83501.
L.Scott Mills, Wildlife Biology Program, University of Montana, Missoula, MT 59812.
Wayne Wakkinen, Idaho Department of Fish and Game, HCR 85 Box 323-J, Bonners Ferry ID 83805.
David Tallmon, Division of Biological Sciences, University of Montana, Missoula, MT 59812.

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