Periodic Status Review for the Woodland Caribou (2017)

Woodland caribou (Rangifer tarandus caribou), a subspecies of caribou, occur across the boreal regions of North America and are comprised of eight recognized populations.  The southern mountain caribou population consists of 17 subpopulations, or herds, with the South Selkirk subpopulation being one of these.  This subpopulation occurs in the southern Selkirk Mountains of southeastern British Columbia, northeastern Washington (in Pend Oreille County), and northern Idaho, and is the only caribou herd that ranges into the contiguous U.S. 

Southern mountain caribou are distinguishable from other populations of woodland caribou by their inhabitation of mountainous areas with deep snow accumulations and their winter diet of primarily arboreal lichens.  These caribou prefer large areas of late successional conifer forests throughout the year and migrate seasonally to different elevations and forest types to seek food and suitable calving sites. 

Overall abundance of southern mountain caribou has declined 45% since the late 1980s and was estimated at 1,544 animals during 2008-2014.  Eleven of the 17 subpopulations show declining trends, nine hold fewer than 50 animals, and two have been extirpated since 2003.  The South Selkirk subpopulation was considered abundant and possibly numbered in the hundreds in the late 1800s, but decreased to an estimated 25-100 caribou between 1925 and the mid-1980s.  Numbers ranged between 33 and 51 animals from 1991 to 2009 despite being supplemented with 103 caribou in two separate multi-year translocations in the late 1980s and 1990s.  Most recently, the subpopulation declined rapidly from 46 to 12 caribou between 2009 and 2016.  The percent of calves in the subpopulation during late winter surveys averaged 9.9% per year from 2004 to 2016, which is below the estimated 12-15% needed to maintain a stable population with high adult survival.  Additionally, the South Selkirk subpopulation is isolated from neighboring subpopulations, with probably no immigration occurring in recent decades.

Predation is considered the most immediate threat to the South Selkirk subpopulation.  Although robust caribou populations are able to withstand some level of natural predation, any amount of predation on the now very small South Selkirk subpopulation is likely to greatly affect its future sustainability.  In addition, past conversion of old-growth forests to earlier successional stages has brought higher densities of deer, moose, and elk and their predators (i.e., wolves, cougars, and bears) into closer proximity to herd members, resulting in greater predation risk to caribou.  Other threats to the subpopulation are highway collisions, human disturbance associated mostly with winter backcountry recreation, small population size coupled with isolation, and climate change.

The small size and ongoing decline of the South Selkirk subpopulation has increased its risk of extirpation.  It is therefore recommended that woodland caribou remain a state endangered species in Washington.