Over the course of nearly five years, a female gazelle in Mongolia completed a remarkable journey of at least 18,000 kilometers (11,185 miles). It crossed frozen rivers, encountered oil fields, negotiated fenced boundaries with China and Russia and trekked 900 kilometers just to survive two months of one particularly brutal winter, according to a new study.
Extremely long journeys might not be unusual for Mongolian gazelles (Procapra gutturosa), but technology that enables finely detailed tracking of migrating mammals has only become available in the past two decades. Combining their latest findings with past observations of Mongolian gazelles, the study’s authors concluded that lengthy treks by these midsize antelopes “occur frequently and that this was simply the first time we were able to observe them.”
The cumulative distance traveled by this gazelle during the study period corresponded to almost half of the circumference of Earth’s equator. It would take more than a year for a human walking 12 hours daily on a flat land to complete a journey of that distance, according to one walk-time calculator. Other hoofed mammals, or ungulates, that have made recently documented journeys include a white-eared kob (also a type of antelope) that completed an 860-kilometer ring-shaped route spanning South Sudan and Ethiopia in 13 months, according to a 2018 master’s thesis by Kasahun Abera Legesse of Addis Ababa University in Ethiopia.
More than half of the world’s gazelles of the species P. gutturosa live on Mongolia’s Eastern Steppe, says wildlife ecologist Nandintsetseg Dejid of the Senckenberg Biodiversity and Climate Research Center in Germany, who led the new study.
This particular animal’s seemingly random path and exploration of unfamiliar areas—likely driven by a search for food and friendly weather conditions—should be seen as nomadic movement, Dejid and her colleagues wrote in their study, which was published on February 9 in Ecology. Nomadic ungulates “need to track changing resources at a landscape scale [that] are driven by highly dynamic precipitation between years,” Dejid says. Nomadism is distinct from migration, she adds, describing the latter as a seasonal movement that typically returns an animal to a prior homeland, birthplace, calving ground or favored haunt.
The length and sprawl of this gazelle’s trek reveal that vast expanses of unfenced land are essential to the survival of nomadic ungulates, says Dejid, who also studies the movements of gray wolves and Przewalski’s horses in Mongolia. Veterinarian and wildlife epidemiologist Enkhtuvshin Shiilegdamba, director of Wildlife Conservation Society Mongolia, agrees that the gazelle’s long and unpredictable route shows how crucial open space is for efforts to conserve Mongolian gazelles. Shiilegdamba was not involved in the new study.
In October 2014 Dejid and her colleagues outfitted 14 Mongolian gazelles with lithium-battery-powered GPS collars that transmitted location signals every 23 hours and provided up to a few years of data. But a 15th gazelle—the individual highlighted in the new study—received a solar-powered GPS collar that outperformed the others and enabled the new findings. “I have always been grateful for this extraordinary individual, which moved extremely long distances during the extreme winter of 2015 to 2016 and survived. I loved watching her movement tracks,” Dejid says.
In August 2019 a signal sent by the solar collar indicated that the gazelle might have died. A month later Dejid embarked on her own trek to investigate the case, setting her sights on the last coordinates the collar had transmitted. “I traveled over 900 kilometers by car to the steppe to retrieve the GPS collar because I wanted to know more about where she died and why,” Dejid says.
The trail led to a family of herders who had found the collar and stored it in their yurt. Their dogs likely injured the gazelle’s hip and caused a fatal maggot infestation, Dejid says.
The gazelle’s remarkable ramble contrasts sharply with the extremely predictable seasonal movements of mule deer herds studied by wildlife ecologist Matthew Kauffman of the U.S. Geological Survey’s Wyoming Cooperative Fish and Wildlife Research Unit. One mule deer among a group in Wyoming migrated about 250 kilometers along a familiar corridor from its winter range to its summer range, Kauffman and his colleagues reported in 2019. “When we track that animal coming back, they are within 300 meters of the previous year’s route,” he says. “They are basically walking in their own footprints coming back.”
The kinds of journeys made by ungulate species likely reflect variations in the predictability of food sources and weather patterns, Kauffman says. Year after year, mule deer in Wyoming spend their summers in mountain areas that reliably provide good foraging and spend their winters in valleys protected from harsh weather. The gazelles on the more dynamic Eastern Steppe of Mongolia do not have it so easy. “They are making a good living, but they have to do it by exploiting these huge landscapes,” Kauffman says. The Mongolian gazelle is designated as a “least concern” species on the International Union for Conservation of Nature’s Red List of Threatened Species, although it is regionally endangered, according to the 2006 Mongolian Red List of Mammals.
More broadly, long-distance journeys by ungulates are decreasing at a high rate because of human-erected barriers such as highways, fences, energy developments and commercial agriculture, Kauffman and his colleagues wrote in Science in 2021. A 2009 study synthesizing migration data on 24 large-bodied ungulate species turned up concerning results: Migration was extinct or unknown in status among six of these species, the researchers reported. And fewer individuals of several ungulate species were found to be migrating.
In some cases, the inability to make long trips can result in die-offs among migrating mammals—which occurred to Cape springbok in the Karoo region of South Africa at the end of the 19th century—or contribute to the eradication of a species, Kauffman and his co-authors wrote in their 2021 paper.
Some ungulate populations that lose part or all of their movement corridors might survive, but their knowledge of when and where to migrate—a behavior that includes nomadic or less predictable journeys such as those made by the Mongolian gazelles, as Kauffman sees it—might die out over time. This pattern occurred among moose and bighorn sheep that became nearly extinct in some areas of North America, he and his colleagues noted in the 2021 paper.
Reintroduced populations of the moose and sheep lacked knowledge in their new home areas of when and where to migrate in order to find good plants to eat at the right time of the year. But subsequent generations of the animals eventually started to migrate again, possibly after their forebears checked out foraging opportunities in higher ground one summer and passed on that knowledge to offspring, as was documented by wildlife ecologist Brett Jesmer, Kauffman and others in 2018. This finding led the researchers to confirm a hypothesis that migration was a learned behavior, essentially taught or transmitted socially among individuals in groups of ungulates.
Vanishing migrations also can have negative consequences for human cultures intertwined with migratory animals and for ecosystems, Kauffman says. Some animals prey on ungulates, and numerous organisms depend on the biological activity sparked by hooves and the spreading of seeds and other material in migrators’ urine and feces.
More comprehensive global maps of mammals’ migration routes based on high-resolution GPS-collar data could help guide efforts to avoid constructing new barriers to ungulates’ long-distance journeys. Three years ago Kauffman and several of his colleagues, including Thomas Mueller of the Senckenberg Biodiversity and Climate Research Center, who was Dejid’s co-author on the new paper, started a mapping project now called the Global Initiative on Ungulate Migration.
The Mongolian gazelles studied by Dejid pose a tough conservation challenge, given their unpredictable pattern of movement on lands where oil, gas and transportation infrastructure are expected to expand and fragment more of the open areas, Kauffman says. “Where on this landscape do we need to keep it open in order to allow movements like this one to continue?” he adds. “That question is really challenging because the movements aren’t predictable from one year to the next.”