Reindeer populations are in decline across their circumpolar range, which encircles the high latitude Northern Hemisphere. This medium-sized member of the deer family (Family Cervidae) is important to subsistence lifestyles of aboriginal people in northern Canada, Alaska and Greenland, to Sami people of Scandinavia, and to many Indigenous peoples of Siberia. Reindeer are notable in modern times as a symbol of transporting Santa Claus on Christmas Eve. Reindeer (Rangifer tarandus), also known as Caribou in North America, are central to nutrient cycling on the tundra and are a main prey species for northern carnivores, including wolves (Canis lupus), bears (Ursus arctos and U. americanus), wolverine (Gulo gulo) and lynx (Lynx canadensis and L. lynx).
Seven subspecies of caribou and reindeer are currently recognized. Barren-ground caribou (R.t. groenlandicus) reside in herds often numbering >10,000, and undertake long seasonal migrations between tundra summer ranges and taiga winter ranges in northern Canada and Greenland. Grant's caribou (R.t. granti) share similar life history traits to barren-ground caribou, but are found west of the Brooks Mountain Range in Alaska. Reindeer (R.t. tarandus) are found across the tundra and taiga of northern Norway, Sweden, Finland and Siberia. Like North American caribou, they migrate in large herds between distinct summer and winter ranges. Unlike caribou, numerous semi-domestic reindeer populations exist, and these are herded by numerous Indigenous peoples (e.g. Sami, Eveny, Komi) for meat, milk and hides. Svalbard reindeer (R.t.platyrhynchus) are found only on the Svalbard Islands, north of Norway. This subspecies is shorter and fatter than other reindeer subspecies, since it does not coexist with predators. Peary caribou (R.t. pearyi) are genetically and morphologically similar to Svalbard reindeer, but are found on the high arctic islands of Canada. Woodland caribou (R.t. caribou) are found in parts of Canada's boreal forest. Unlike other Rangifer subspecies, woodland caribou live in small groups (typically less than 100) and do not undertake long seasonal migrations. Forest reindeer (R.t. fennicus) are the Scandinavian analogue of woodland caribou, also residing in small groups and residing within the boreal forest year-around.
Caribou and reindeer around the world are currently in decline. Recent research suggests that caribou and reindeer numbers have fallen by approximately 60% over the past 30 years. There are multiple factors behind this population decline, factors linked to global climate change and industrial landscape change within caribou and reindeer habitat. The influence of climate oscillation versus industrial landscape change varies depending on whether a caribou or reindeer population is migratory or non-migratory.
Changes in insect and plant phenology
Progressively earlier insect seasonal emergence as a forest disturbance in the Arctic insect, and earlier plant emergence are consistent with warming trends, and these factors may have negative effects on caribou/reindeer body condition and thus population dynamics. A number of insect species, including mosquitoes (Aedes spp.), warble flies (Hydoderma tarandi) and nose bot flies (Cenephemia trompei) harass and parasitize caribou. The abundance and activity level of these insects is positively correlated with ambient temperature, and caribou or reindeer that are harassed by these insects spend less time feeding. They also expend considerable energy using "escape" behaviours such as running around and shaking themselves to avoid being bitten. When caribou or reindeer feed less in the summer, they gain less body mass. If they do not gain enough fat or muscle prior to winter, females are less likely to conceive. Over-winter survival of poorly-nourished indivduals is also poor.
The timing of calving in spring is closely tied to the timing of plant emergence. However, caribou appear not to have adjusted their calving period to coincide with earlier plant emergence. Early-emergent plant matter is more nutritious than older, senescent plant matter, and if caribou calves and their dams miss out on this flush of plant growth, calf survival and female body condition may suffer.
Migratory caribou and reindeer appear to be most affected by these changes. In short, factors that compromise the nutritional status of caribou and reindeer generally lead to decreased survival and productivity.
Extreme weather events
Increased precipitation may accompany warmer winters in the Arctic, especially in the form of freezing rain. When freezing rain falls over snow and forms an impenetrable ice layer, this is termed an "ice on snow event." These ice on snow events may prevent caribou and reindeer from reaching their winter forage. Caribou and reindeer feed chiefly on lichens in the winter and cannot readily dig through ice to reach this forage. Ice on snow events are implicated in population declines of caribou and reindeer living on islands, where they do not have the option of moving to different wintering grounds. Indeed, ice on snow events are linked with mass starvation and decline of Peary caribou, as well as past population declines of Svalbard reindeer. Ice on snow events also significantly impact over-winter survival of semi-domestic reindeer, which typically have smaller winter ranges than wild populations.
Industrial change: changes in predator-prey dynamics
The persistence of non-migratory woodland caribou is threatened by industrial landscape change, because landscape change alters how woodland caribou interact with their chief predator, the wolf. Forest overharvesting and certain petroleum infrastructure (e.g. seismic lines) have removed large areas of old-growth coniferous forest, the preferred habitat of woodland caribou, leading to early seral stage forest regrowth. This new growth is ideal moose and deer habitat, and these species are able to support large wolf populations because they have a higher reproductive rates than caribou. The predator population becomes larger than what the caribou population can support, leading to shrinking woodland caribou numbers.
The loss of caribou and reindeer populations will have significant adverse consequences for the northern indigenous peoples who rely on this species for subsistence. Not only are caribou and reindeer a source of economic value, e.g. meat, but they sustain countless cultural values including education in traditional ways of life, spirituality and kinship/bonding through hunting and herding caribou and reindeer. Declining caribou and reindeer populations may have negative consequences for nutrient cycling on the tundra, since defecation by caribou/reindeer returns nitrogen to the soil which, in turn, may increase diversity of plant and invertebrate assemblages. Whether caribou and reindeer populations will recover from the current decline is unknown. Although the species population numbers have fluctuated in the past, recovery from past declines does not guarantee recovery from future declines. Indeed, the fate of this species will likely be determined by the pace of climate change and industrial development.
- M.A.Cronin, M.D.Macneil and J.C.Patton. 2005. Variation in Mitochondrial DNA and Microsatellite DNA in Caribou (Rangifer tarandus) in North America. Journal of Mammalogy 86(3): 495–505
- Peter Gravlund, Morten Meldgaard, Svante Pääbo, and Peter Arctander. 1998. Polyphyletic Origin of the Small-Bodied, High-Arctic Subspecies of Tundra Reindeer (Rangifer tarandus). Molecular Phylogenetics and Evolution 10 (2): 151–9
- R.S.Sommer and A.Nadachowski. 2006. Glacial refugia of mammals in Europe: evidence from fossil records. Mammal Rev 36 (4): 251–265