The last woolly mammoth passed away 3,700 years ago on Wrangle Island in northern Siberia. Located in the Chukotka Autonomous Okrug, Wrangle Island is 7,600 square kilometers or just under 3,000 square miles in area. The last mammoth couldn’t have gone very far during his lifetime. But woolly mammoths living in prehistoric Alaska roamed far and wide, it turns out.
One woolly mammoth who lived 17,000 years ago in Alaska covered enough ground in its 28 years of life to almost circle the Earth twice, according to a new study published in Science.
How do we know this? The journey of this itinerant Arctic elephantid, whose remains were found in Alaska’s North Slope above the Arctic Circle, was reconstructed by an international team based on isotope signals in one of its tusks. The tusk has been kept at the University of Alaska Museum of the North.
It’s worth noting that modern-day elephants are semi-migratory, which means, they may roam afar when necessary. Or they may not. Both the Indian (Asian) and African versions of elephant tend to migrate with the rain, which is why ecologists refer to them as opportunistic partial migrants, in contrast to animals like the wildebeest or monarch butterfly, which migrate seasonally, en masse.
In other words, in proboscidean circles, some members of a herd may migrate and some may not. A 2018 study published in Nature suggested that the drivers of elephant migration “are likely a complex interaction between individual traits, density, and the distribution and availability of resources.”
We can’t definitively say whether woolly mammoths were migratory or not but the new study shows that a specific woolly mammoth definitely got about.
“It’s not clear-cut if it was a seasonal migrator, but it covered some serious ground,” remarked University of Alaska Fairbanks researcher Matthew Wooller, senior and co-lead author of the paper. “It visited many parts of Alaska at some point during its lifetime, which is pretty amazing when you think about how big that area is.”
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A mammoth’s diary
The record of the mammoth’s journey is stored in its tusks, somewhat like the rings of a tree. Tusks add new layers on a daily basis throughout the proboscidean’s life.
“From the moment they’re born until the day they die, they’ve got a diary and it’s written in their tusks,” said paleontologist Pat Druckenmiller, director of the UA Museum of the North.
Elephants are herbivores. Plants exhibit the isotope composition of the land where they grow. When the elephants eat the plants, the isotopes are transferred to them. A new layer of tusk reflects the isotopes of the plants that the elephantid most recently ate.
All that remained was to identify the isotope signals in the different layers of the animal’s tusk (its “diary,” or maybe “travelogue”) and compare it with an isotope map of Alaska.
The only snag is that there wasn’t one. The researchers created an isotopes map for Alaska by analyzing the teeth of hundreds of small rodents from across Alaska that were held in the museum’s collections.
Why is a collection of dead rodents helpful? Because most rodents are not migratory and, therefore, a rodent’s isotopes represent the local situation.
To be clear about rodent migration: there has been quite the heated debate about whether “migrating rats” spread the plague, but they aren’t migrating in the usual sense of the word. For instance, one cannot call the history of our friend the brown rat, which originated in southeast Asia and colonized new continents by human agency, such as stowing away on ships, a story of migration. Rats may change neighborhood and mice may move with the humans whose granaries provide their meals, but rodents can’t get that far on their tiny little legs. So we can assume that a rodent’s isotope signal is local.
Back to our massively mobile mammoth: His diary was written in isotopic signatures of strontium and oxygen in one six-foot tusk split down its length and analyzed at the Alaska Stable Isotope Facility.
After taking geographic barriers into account and the average distance the lad traveled each week, the team could chart a postulated path the animal took during its lifetime.
The reason behind the study, curiosity aside, was to look at how environmental changes and human agency affected woolly mammoth populations, with an eye aimed at investigating mass extinctions. Previously, we knew nothing about the home range of a mammoth, though it was assumed that it covered vast distances. Now we know.
Genetic analysis shows this long-deceased Ice Age elephantid was a male, and was apparently related to the last group of its species that lived in mainland Alaska – they died about there about 13,000 years ago.
When he was young, the mammoth lived, according to the isotope signature, in the lower Yukon River basin, in the interior. After age 2 he began to roam farther afield, likely with the herd of females and their kids, the team surmises.
From about age 15-16, an abrupt change in isotopic signatures reveals that our mammoth trekked even farther, which the researchers surmise may be because he was maturing and was kicked out of his mother’s herd. Among elephants, bulls may abandon the matriarch-dominated herd when they grow up and lead solitary lives or sometimes coalesce to form all-bull groups.
“Knowing that he was male provided a better biological context in which we could interpret the isotopic data,” adds Beth Shapiro of the University of California Santa Cruz and investigator at the Howard Hughes Medical Institute, who led the DNA component of the study.
The isotopes may also shed light on his demise. As the Ice Age waned following the Last Glacial Maximum, the climate changed and warmed in the far northern hemisphere. It’s likely that he couldn’t get around as he had been accustomed to doing. A spike in his nitrogen isotopes indicates that the unfortunate animal starved.
As for the very last woolly mammoths who lived on that Siberian island above the Arctic circle, they had a different problem. Not only were they isolated and range-bound, they apparently became fatally inbred.