'Lost' Caribou Herd Not Global Warming Victim: It Simply Moved

Caribou are considered vulnerable to the effects of predicted global warming (Johnson and Barrier, 2011; Wilson et al., 2011) and in part because of this, efforts have recently intensified to monitor and quantify caribou populations everywhere (Kafinas et al., 2011). While caribou numbers and movements are known to vary unpredictably (Parlee et al., 2005; 2011), one subpopulation, the Beverly barren-ground herd that migrates annually between northern Saskatchewan to Nunavut, recently became the topic of special concern. Aerial surveys in 2009 revealed only a few Beverly cows had arrived on their traditional summer calving grounds. The herd, which once numbered over 250,000 animals, appeared to have simply vanished after a few short years of ever-increasing declines (CBC News, 2008). Global warming was one suggested culprit, although mining activity and hunting were also blamed. Other caribou subpopulations across the Arctic have also documented significant (although less dramatic) declines in recent years.

The latest update on the subject comes from a 2011 paper by Nagy and colleagues (Nagy et al., 2011), who conducted a comprehensive population study of several Canadian caribou subpopulations. By placing radio-collars on a number of animals over a period of 13 years (1996-2008) Nagy et al. were able to track caribou movements year round. More animals were collared in 2006-2008 than the years previous. The authors then analyzed satellite-tracking data "to quantify subpopulations within the behaviorally different barren-ground caribou (Rangifer tarandus groenlandicus), Dolphin and Union island caribou (R. t. groenlandicus x pearyi), and boreal (R. t. caribou) caribou ecotypes in the Northwest Territories and Nunavut, Canada." Previously, population estimates had been based on aerial surveys during the summer calving period (e.g. Nagy et al. 1996).

The results showed first and foremost that the Beverly herd was safe and sound: most of the cows had simply switched to using another calving ground, as native elders had predicted would be the case (Weber, 2011). The authors determined that "One barren-ground subpopulation used two calving grounds, and one calving ground was used by two barren-ground subpopulations, indicating that these caribou cannot be reliably assigned to subpopulations solely by calving-ground use. They should be classified by annual spatial affiliation among females." Although no new subpopulation estimates were provided, the authors seem to imply that previous population size declines (based on aerial surveys) may have been inflated because some caribou cows chose to give birth outside their traditional calving grounds and were not counted.

In any case, global warming was not to blame for the 'lost' Beverly caribou herd (nor were hunting or mining activities). The 'fault' appeared to lie with the survey strategy used by wildlife biologists, which depended on designating 'traditional' calving grounds to define caribou subpopulations and track their numbers. When caribou cows switched calving grounds, as they have done in the past (Parlee et al., 2005; 2011; Weber, 2011), they did not get counted. This study, therefore, is a reminder that reports of 'missing' populations or dramatic declines in numbers should be taken with a grain of salt until proper scientific analyses can be performed, especially for animals with enormous species ranges that are difficult to survey.

Additional References
CBC News. 2008. Another caribou herd in steep decline: study. CBC News, Dec. 1, 2008. http://www.cbc.ca/news/technology/story/2008/12/01/caribou-decline.html. Accessed Dec. 7, 2011.

Johnson, C., and Barrier, T. 2011. Wildfire, habitat and harvesters-understanding distribution of Bathurst caribou during winter. pg 39 in: Abstracts of the 13th International Arctic Ungulate Conference, Aug. 22-26, Yellowknife, Northwest Territories, Canada.

Kafinas, G., Russel, D., Ashenfelter, R., Griffith, B., and Gunn, A. 2011. The challenges ahead: CARMA after International Polar Year (IPY). pg. 70 in: Abstracts of the 13th International Arctic Ungulate Conference, Aug. 22-26, Yellowknife, Northwest Territories, Canada.

Nagy, J.A., Larter, N.C., and Fraser, V.P. 1996. Population demography of Peary caribou and muskox on Banks Island, N.W.T., 1982-1992. Rangifer 9: 213-222.

Parlee, B., Caine, K., Manseau, M. and Simmons, D. 2011. "When the caribou do not come..." resilience to caribou population change in the western Arctic. pg. 92 in: Abstracts of the 13th International Arctic Ungulate Conference, Aug. 22-26, Yellowknife, Northwest Territories, Canada.

Parlee, B., Manseau, M. and Lutsël K'é Dene First Nation. 2005. Using traditional knowledge to adapt to ecological change: Denésoliné monitoring of caribou movements. Arctic 58: 26-37.

Weber, B. 2011. Canadian elders right all along, 'lost' caribou had just moved. The Toronto Star, Nov. 21. http://www.thestar.com/News/Canada/article/1090179. Accessed Nov. 22, 2011.

Wilson, R., Prichard, A., Parrett, L., Person, B., and Carroll, G. 2011. Seasonal resource selection by the Teshekpuk caribou herd. pg. 38 in: Abstracts of the 13th International Arctic Ungulate Conference, Aug. 22-26, Yellowknife, Northwest Territories, Canada.