Who Goes Farthest?

Caribou often are mentioned as the animals with the longest overland migrations in the world, although there’s never been much scientific support for the claim, until now. 

An international team of scientists gathered GPS collar data from around the globe to answer the question of which large terrestrial mammal migrates the farthest. Recognizing that not all mammals migrate, the team also determined how far non-migratory mammals moved during the course of a year. 

The research team—which includes Eliezer Gurarie, an associate research scientist in the UMD Department of Biology, Kyle Joly of the National Park Service and Mark Hebblewhite of the University of Montana—published its findings on Oct. 25 in the journal Scientific Reports.

And as conventional wisdom suggested, caribou from numerous populations had the longest existing migrations, with round-trip distances exceeding 745 miles. A few species such as gray wolves and khulan, or 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, traveling 4,503 miles in a year, the equivalent of a walk from Washington, D.C., to Los Angeles and back. 

"What was fascinating about this study is how quickly it escalated,” Gurarie said. “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, human impacts."

The team discovered interesting patterns among these big movers. First, not only can predators keep up with their prey, they often have to move much more in the course of their search for a meal. In Mongolia, gray wolves traveled farther than their prey, the khulan and Bactrian camel. 

In Alaska, it was the same for gray wolves compared to caribou or moose. 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.

One possible explanation for this pattern is that large animals can use lower quality food sources that are more abundant, allowing them to move less overall. Lastly, higher movement rates by herbivores were associated with areas of 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 according to the researchers, highlights the effects of habitat fragmentation and human development.

Threatened worldwide, long-distance migrations are critical for the conservation of many iconic species. Understanding migration and animal movement through studies like this is key to effective wildlife management and conservation.

“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,” Hebblewhite said. “Our study builds on a growing body of science that shows 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.”

The National Park Service contributed to this article.