Caribou are often credited with the longest terrestrial migrations in the world, though without much scientific support. Our international team of scientists gathered GPS collar data from around the world to address the question: which large terrestrial mammal migrates the farthest in the world? Long-distance migrations are threatened around the world, yet are critical for the conservation of many iconic species. Recognizing that not all mammals migrate between ranges, our team also determined how far these mammals moved during the course of a year.
Caribou migrating through Kobuk Valley National Park, Alaska - Kyle Joly
We measured 2 metrics of movement: round-trip migration distance (distance between the start and end of migration) and total annual movement (total distance the animal moved in a year from GPS collar data). We found that caribou, from numerous populations, were indeed do have the longest existing migrations, with the round-trip distances exceeding 745 miles (1,200 km). Surprisingly, a few species such as gray wolves and khulan (Mongolian wild ass), while not migrating in a regular manner like caribou, traveled even greater annual distances. A gray wolf from Mongolia captured the title of top terrestrial mover, having traveled 4,503 miles (7,247 km) in a year, the equivalent of a walk from Washington, DC to Los Angeles….and back. "What was fascinating about this study is how quickly it escalated. What started as a narrow effort to set the record straight on caribou migration morphed into this globe-spanning survey of long-distance movement - and then touched on all kinds of ecological relationships, between predator and prey, habitat features, and human impacts." says Dr. Elie Gurarie, who was part of the study.
Wolf and khulan in Mongolia - Petra Kaczensky
Our team discovered interesting patterns among these big movers. First, not only can predators keep up with their prey, they are often required to move much more in the course of their search for a meal. In Mongolia, Alaska, and Alberta, gray wolves moved more than their prey, the khulan, wild camel, caribou, moose and elk. Second, small prey animals from the same region tended to move more than larger ones. For example, wildebeest moved more than zebras in the Serengeti, caribou more than moose in Alaska, and khulan more than wild camels in Mongolia. We think one possible explanation of this pattern is that large animals are capable of using lower quality food sources which are more abundant, and this allows them to move less overall. Lastly, we found higher movement rates by herbivores were associated with lower vegetative productivity. The less food that was available, the more they moved, likely to acquire sufficient resources. The greatest movements were found in areas of very low human disturbance, which highlights the effects of habitat fragmentation and human development. Dr. Mark Hebblewhite, also a team member of the study, notes that “One of the most amazing aspects of this study is the simple fact that large mammals, from around the globe, need so much habitat to move. Seasonal migrations, predator-prey dynamics, and the need to obtain food drive these astonishing long-distance movements. Our study builds on a growing body of science that show human activity can negatively affect animal movements and populations, and our work emphasizes the need to maintain core habitats and connectivity to keep these animals on the move.”
Gray wolf in Yukon-Charley Rivers National Preserve, Alaska - Kyle Joly