Behavioral adaptation to seasonal resource scarcity by Caribou (Rangifer tarandus) and its role in partial migration

Animals living in seasonal environments have adopted a wide array of tactics used to deal with seasonal resource scarcity. Many species migrate between habitats to reach areas where food resources are more plentiful as an attempt to address energetic demands through foraging. We assessed the winter behavioral adaptations of Caribou (Rangifer tarandus), a large ungulate inhabiting Arctic and sub-Arctic regions known for seasonal resource scarcity. Movement rates of Caribou are the lowest of the year during winter, revealing 1 mechanism individuals use to reduce energy expenditures. However, migratory individuals moved nearly twice as much as nonmigratory individuals during winter, suggesting that migratory individuals rely more upon income (forage), whereas nonmigratory individuals rely more upon capital (bodily reserves). Lichens are the primary winter forage for large, migratory herds of Caribou, and migratory individuals experienced more than 2.5 times greater lichen cover than nonmigratory individuals. We documented that both groups slowed their movement in areas of greater lichen cover, suggesting increased foraging time in these areas. Movement rates were greater near villages, which may be suggestive of disturbance, but the effect was weak. Overall energy saved by reduced movement rates was modest. However, energy savings were 11% of daily body energy lost or 47% of the demands of early pregnancy, which potentially could affect individual condition and/or fetal growth if not offset by increases in forage intake.