How Scientists Tracked the Movements of a 17,000-Year-Old Woolly Mammoth

The arctic woolly mammoth named Kik, one of the only Ice Age mammals whose life story is known in detail, was born approximately 17,100 years ago in the Alaskan interior, a region bounded by the Brooks Range to the north and the Alaska Range to the south. Back then, the area was a cold, dry grassland that extended across the Bering land bridge into Siberia, and all the way to western Europe. Paleontologists call this vast region the “mammoth steppe” after the largest animals that traversed it.

Adult male woolly mammoths reached a height of 12 feet at the shoulder, with a thick hide, shaggy coat and tusks up to 12 feet long. No predator could bring down an adult, but young mammoths, likely standing about four feet tall, were prey to scimitar-toothed cats. Kik and his herd-mates would have kept a wary eye on these predators, which weighed more than 500 pounds, with serrated canines that could bite through mammoth hide. Beringian lions were another threat; also on the landscape were steppe bison, giant short-faced bears and the gray wolves and brown bears we see today.

For the first two years of his life, Kik mostly stayed in the lower Yukon River basin, almost certainly in a matriarchal herd. Over the next 14 years, the juvenile’s range expanded dramatically. Still probably traveling with the herd, he made regular back-and-forth journeys across the 250-odd-mile stretch of steppe grassland between the Brooks Range and the Alaska Range. Sometimes he ventured to the eastern end of the Brooks Range. He also traveled to the Seward Peninsula on today’s west coast, a journey of more than 700 miles. Although the data suggests that for much of his life, he seldom covered less than ten miles in a day, we now know that over the course of his lifetime, Kik walked roughly twice the circumference of the earth—much farther than mammoths were thought to travel.

To be able to track an Ice Age animal’s movements in such detail is a stunning milestone in paleontology. It began with a moment of inspired curiosity in the mind of Matthew Wooller, an isotope scientist at the University of Alaska Fairbanks. In 2015 he was in his laboratory, watching one of his graduate students analyze fish otoliths—small ear bones that add a new layer every year and store chemical information about the fish’s life and habitat. “What if we did the same thing with a mammoth tusk?” thought Wooller, an expatriate Englishman with a shaved head and a crisp, upbeat manner. He was already interested in mammoths from studying their extinction on St. Paul Island in the Bering Sea. He compares a mammoth tusk to a diary written in ivory. “It adds a new layer every day, and the layers stack up on each other like ice cream cones,” he says. “The isotopes in those layers record where the animal was and what it ate that day.”

Isotopes are atoms of the same chemical element that have differing weights, because of a greater or lesser number of neutrons. “Think of isotopes as chemical signatures,” Wooller says. “They’re in the rocks, soil, vegetation and water, and creatures pick them up.” These signatures—or “fingerprints,” as they’re sometimes known among researchers—are specific to particular locations. Wooller knew that isotopes in elephant tusks can reveal migration routes. “Where does a mammoth move?” he says. “That was the main question I wanted to answer.”

He began the project in 2016 by crossing campus to the University of Alaska Museum of the North, where 174 woolly mammoth tusks are stored on top of specimen cabinets in a lower level. He selected one that had been collected by the university’s researchers in 2010, near the headwaters of the Kikiakrorak River on Alaska’s North Slope. The mammoth’s jawbone, containing molars the size of a man’s shoe, was collected at the same site. Radiocarbon dating showed that the animal died 17,100 years ago, and genetic testing revealed that it was male. “We nicknamed him Kik after the Kikiakrorak,” says Wooller, who assembled a team of 16 scientists from four different countries to work on the study.

The most physically arduous task was splitting the roughly 50-pound tusk in two. “Six of us fed it through a huge band saw,” Wooller says. “The tusk has a double twist, so you’re constantly making adjustments, and it was cracking and popping like it was going to explode. It took us a whole day.”

Now, the split tusk lies on a laboratory table. Each half is five-and-a-half feet long, stained with blue dye to reveal its growth layers. “The tip of the tusk is the young mammoth, the base is the old mammoth, and everything in between is its lifetime,” Wooller says.

Wooller opens up a remarkable map on a screen. It shows the different regions of Alaska that Kik occupied during the different phases of his life, plus hundreds of his travel routes. Asked how the team managed to map Kik’s life in such detail, Wooller cites a surprising aid: “It’s amazing what voles can tell you. They’re like little citizen scientists.” Since voles have a small range and don’t travel, the isotopes in their teeth record site-specific information about where they lived—allowing Wooller to dig into the past with even more clarity.

In a lower level of the University of Alaska Museum of the North, in the specimen cabinets beneath the mammoth tusks, sits an extensive collection of voles and other rodent specimens collected from all over Alaska. The museum’s director, a paleontologist named Patrick Druckenmiller, who contributed to the Kik study, says strontium isotypes in these rodents’ teeth offered the key mapping aid. “[The] isotopic signature varies from place to place, depending on the underlying geology. Plants absorb strontium from the rock beneath the soil, and animals ingest it through eating plants.”

By analyzing the strontium values in 162 of these rodents, the team was able to build up a strontium map of Alaska. Clément Bataille at the University of Ottawa and Juliette Funck, then a doctoral student at Wooller’s laboratory, created the map. Even though it’s based on data from rodents in the modern era, the map is accurate for the Pleistocene, too, because the underlying rocks are the same. “Strontium values reflect bedrock geology, so they change very, very slowly, over millions of years,” Druckenmiller says.

Meanwhile Wooller and his colleagues were looking at the strontium and other isotopes in Kik’s tusk. Working their way from one end to the other, they cut five-centimeter wedges from the core, mounted them and fed them into a $830,000 scientific instrument called a Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometer. The National Science Foundation awarded a $580,000 grant to help the University of Alaska Fairbanks purchase this instrument, which now resides in a cavernous basement room. It’s the size of a minivan. “It’s down here because we were worried it would break through the floor upstairs,” Wooller says.

The instrument’s 80-micron laser slowly scrolled along each wedge of tusk, turning tiny portions into fine dust. The mass spectrometer then performed a rapid isotopic analysis on the particles. In all, the instrument produced more than 400,000 data points about where Kik was and what he was eating over his lifetime. “We knew where he died, so we traced his travels in reverse,” says Wooller. “By matching the strontium values in the tusk to the strontium map of Alaska, we could see where he’d been, and then we basically connected the dots.” Common sense also helped in mapping Kik’s route: It was reasonable to assume that he wouldn’t have climbed up steep cliffs or over the big glaciated mountain ranges.

After age 16, Kik broadened his range yet further. The researchers think it likely that he left the matriarchal herd to wander alone or with a small group of other males, like a male elephant who has reached sexual maturity. He made many journeys between the Alaskan interior and the North Slope of the Brooks Range, a one-way trip of 700 miles, or closer to 1,000 miles if he meandered while grazing. Wooller suspects Kik was responding to seasonal changes in grasses and plants to eat. To get to the North Slope, Kik favored the same low pass in the western part of the range that migrating caribou use today.

The last year and a half of Kik’s life is recorded in the four inches of ivory at the base of the tusk. The era of long-distance wandering, it appeared, had ended. His range was now restricted to the North Slope. In Kik’s final summer, the nitrogen isotopes in his tusk started to increase. As Druckenmiller explains, “When an animal starts to starve, it essentially eats its own body, and you get a very distinctive nitrogen spike. Why was this animal starving? Was it sick? That would be my guess—but we don’t know.”

The average life span of an Arctic woolly mammoth has been estimated at 60. The evidence suggests Kik died of starvation around the age of 28, in the late winter or early spring, when resources were at their scarcest. He lay down for the last time in the Kikiakrorak River valley, where portions of his skeleton remained for approximately 17,100 years, on a piece of ground that is now part of the headwaters of the Kikiakrorak River, a small tributary of the Colville.

It’s unlikely that Kik ever saw a human, but not impossible. The oldest archaeological site in Alaska is from 14,300 years ago, almost 3,000 years after Kik’s death, but older sites may yet appear. A set of human footprints in New Mexico dating to around 23,000 years ago suggest there were people in North America during Kik’s lifetime. Woolly mammoths went extinct in Alaska around 13,000 years ago; many scientists think human hunters were responsible. Others say climate change was the key.

Wooller thinks it was a combination. “As the climate got warmer and wetter, the grasses were displaced by trees,” he says. “Mammoths were losing their habitat and their ability to move around. At the same time there was a new and very dangerous predator on the landscape—us.”

Having published the study on Kik, Wooller and his colleagues are now analyzing another mammoth tusk. Discovered at an archaeological site in the Alaskan interior, it appears to belong to a female, about 19 years old, who lived around 14,000 years ago. Using the same strontium map and laser ablation mass spectrometer, Wooller’s team is mapping the movements of this animal at a period when humans were on the landscape and shortly before mammoths went extinct in mainland Alaska. “When you’re doing this science, it’s incredibly exciting because it produces a narrative,” says Wooller. “You’re sticking the printouts on the wall, connecting the data points, seeing the story of the animal’s life emerge before you in real time.”

Scientists have pinpointed the many places one woolly mammoth roamed throughout his eventful life
By Ted Scheinman, Map by Haisam Hussein

The tusks of Kik the mammoth offer a remarkably complete biography of the creature. Following a painstaking study of isotopes in the tusk, Matthew Wooller’s team was able to identify the areas where Kik spent time during each stage of his life—traveling to some of the outer ranges of present-day Alaska before meeting his end just north of the Brooks Range. The Last Glacial Maximum refers to a period during the final phase of the Pleistocene, around 20,000 years ago, when glaciers covered 25 percent of the Earth’s land area and the sea level worldwide was roughly 400 feet lower than it is today.