A Synthesis of Scale-Dependent Ecology of the Endangered Mountain Caribou in British Columbia, Canada

A synthesis of scale-dependent ecology of the endangered mountain caribou in British Columbia, Canada Robert Serrouya 1,2, Bruce N. McLellan2, Clayton D. Apps3 & Heiko U. Wittmer4 1 Columbia Mountains Caribou Project, RPO #3, P.O. Box 9158, Revelstoke, British Columbia, V0E 3K0, Canada ([email protected]). 2 British Columbia Ministry of Forests, Research Branch, RPO #3, P.O. Box 9158, Revelstoke, British Columbia, V0E 3K0, Canada. 3 Aspen Wildlife Research Inc., 2708 Cochrane Road N.W., Calgary, Alberta, T2M 4H9, Canada. 4 Wildlife, Fish & Conservation Biology, University of California, One Shields Ave., Davis, California, 95616, USA. Abstract: Mountain caribou are an endangered ecotype of woodland caribou (Rangifer tarandus caribou) that live in high- precipitation, mountainous ecosystems of southeastern British Columbia and northern Idaho. The distribution and abundance of these caribou have declined dramatically from historical figures. Results from many studies have indi- cated that mountain caribou rely on old conifer forests for several life-history requirements including an abundance of their primary winter food, arboreal lichen, and a scarcity of other ungulates and their predators. These old forests often have high timber value, and understanding mountain caribou ecology at a variety of spatial scales is thus required to develop effective conservation strategies. Here we summarize results of studies conducted at three different spatial scales ranging from broad limiting factors at the population level to studies describing the selection of feeding sites within seasonal home ranges of individuals. The goal of this multi-scale review is to provide a more complete picture of caribou ecology and to determine possible shifts in limiting factors across scales. Our review produced two important results. First, mountain caribou select old forests and old trees at all spatial scales, signifying their importance for foraging opportunities as well as conditions required to avoid alternate ungulates and their predators. Second, relationships differ across scales. For example, landscapes dominated by roads and edges negatively affect caribou survival, but appear to attract caribou during certain times of the year. This juxtaposition of fine-scale behaviour with broad-scale vulnerability to predation could only be identified through integrated multi-scale analyses of resource selection. Conse- quently we suggest that effective management strategies for endangered species require an integrative approach across multiple spatial scales to avoid a focus that may be too narrow to maintain viable populations. Key words: caribou, endangered species, landscape, lichen, predation, old-growth forest, Rangifer tarandus, spatial scale. Rangifer, 28 (1): 33 – 46 Introduction Either passively or actively, many organisms applied perspective of maintaining endangered appear to select locations to spend their time species, understanding these broad limiting and exploit resources in a hierarchical man- factors can provide strategic information to ner, ranging from where the species occurs to help decision-makers prioritize core areas for where individuals rest or even what part of a recovery within a species’ range (Channell & plant or animal they consume (Johnson, 1980; Lomolino, 2000). Wiens et al., 1986). At broad scales, the distri- At intermediate scales, such as within a home bution of a species is often limited by coarse range, individual animals may select habitat at- factors such as climate and geology. From the tributes such as a specific forest type or ter- Rangifer, 28 (1), 2008 33 rain feature. When linked to demographic in- almost exclusively on arboreal lichen, particu- formation, this scale of habitat selection can larly late in winter (mid January to mid April) reveal how individual choice affects the fitness when deep snow (1–4 m) covers all terrestrial of the population (Fretwell & Lucas, 1970). foods (Rominger & Oldemeyer, 1989, 1990; Translating such habitat-specific information Seip, 1992; Rominger et al., 1996). into management prescriptions often forms Mountain caribou are confronted with at the basis of local land-use plans, which specify least 2 management challenges: First, unsus- amounts and types of certain habitat features tainable predation has recently been the major that should be maintained (e.g., KBLUPO, factor causing population declines (Wittmer et 2002; RHLPO, 2005; RIP, 2005). al., 2005a). Apparent competition (Holt, 1977, At the finest scales, resource selection for 1984) leading to high predation rates appears features such as nesting, bedding, and feed- to be the proximate mechanism of the current ing sites and corresponding diet may indicate decline (Seip, 1992; Wittmer et al., 2005a, b). functional requirements of both applied and Apparent competition occurs where the abun- theoretical value. Examining these finer scales dance of one prey species negatively affects often reveals ecological mechanisms that ex- the abundance of another through a shared plain broader-scale descriptions of habitat se- predator. Although not thought to be cur- lection (Wiens, 1989). In an applied sense, this rently limiting caribou (Wittmer et al., 2005b), level of knowledge helps to focus conserva- the second challenge is to maintain a continu- tion actions to specific areas that contain criti- ous supply of available and efficiently obtained cal habitat attributes or to modify activities to forage. Because snow is substantially deeper in either maintain or recruit these attributes. areas occupied by mountain caribou than else- The woodland caribou (Rangifer tarandus where within woodland caribou range, winter caribou) is a subspecies of concern in British foraging opportunities are more limited. These Columbia, particularly the endangered “moun- caribou forage mainly on arboreal lichen, but tain caribou” ecotype that lives in the interior because trees with sufficient lichen accumula- wetbelt1 (Heard & Vagt, 1998). The distribution are older than will be grown during a typi- tion and abundance of mountain caribou has cal forestry rotation, a conflict exists between declined significantly over the past several de- forests managed primarily for fibre extrac- cades. In 2006, the entire population consist- tion and for caribou winter foraging habitat ed of approximately 1900 individuals (Hatter, (Rominger & Oldemeyer, 1989; Kinley et al., 2006) distributed over 18 distinct subpopu- 2003; Serrouya et al., 2007). lations (Wittmer et al., 2005a), although two Because mountain caribou have been studied are thought to be recently extirpated (Hatter, at varying intensities across their entire distri- 2006). bution, researchers have been able to examine Mountain caribou (Heard & Vagt, 1998) factors that affect mountain caribou ecology differ from other woodland caribou ecotypes across multiple scales. Multi-scale investiga- (e.g. Bergerud & Elliot, 1986; Rettie & Messier, tions are important because what is considered 1998; McLoughlin et al., 2003) in that they feed available to an animal affects the interpretation of results, as much as what the animals actu- 1 In some other jurisdictions, the term “mountain cari- ally use (Garshelis, 2000). Habitat relationships bou” refers to another ecotype of woodland caribou inhabiting mountainous areas but not primarily reliant may change, sometimes dramatically, when on arboreal lichen. See Heard & Vagt (1998) or Witt- considered across different scales. As animals mer et al. (2005a) for a range map. appear to select resources hierarchically across 34 Rangifer, 28 (1), 2008 spatial scales, managers that operate at differ- Results and discussion ent spatial scales (from recovery prioritization Broad scales: caribou distribution and limiting factors among populations to deciding which tree is Woodland caribou were once much more nu- cut) require information appropriate for each merous and widespread in British Columbia as scale. Therefore, our goal in this review is to well as Idaho, Montana, and Washington State. summarize factors affecting mountain caribou Early verbal and written accounts of large ecology at three spatial scales (Johnson, 1980): herds of caribou that were of great significance 1) Factors limiting distribution and abundance to native North Americans have been summa- (first order); 2) habitat selection within the rized by Spalding (2000). Based on these ear- range of a subpopulation (second order), and ly accounts, it appears that populations have 3) selection of feeding sites and foraging in- declined dramatically in all portions of their tensity of different forage items within season- range. In the south and southwestern portions al home ranges (third and fourth order). Not of their range the major declines and extirpa- only does this multi-scale approach provide a tions occurred near the end of the 1800s and more complete view of caribou ecology, but first two decades of the 1900s. In the central it enables an examination of how factors may and northern portions of the range, the major shift in importance across scales as the per- declines occurred in the 1930s (Spalding, 2000). spective of investigation changes. Overhunting by both native peoples who recently acquired repeating rifles and for some Methods groups that had also lost bison (Bison bison) as Mountain caribou have been monitored us- a major component of their diet (McDonald, ing radio-telemetry across their entire range. 1996) and newly arrived miners and settlers, In some areas caribou have been

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