One of the last known populations of woolly mammoths lived on the tiny island of St. Paul in the Bering Sea. In Eurasia and North America, these large creatures died out toward the end of the last ice age — about 12,000 years ago — but the St. Paul population survived for thousands of years longer because they had no predators and plenty of food and water.
But about 7,600 years ago, they too went extinct. The answer as to why has remained large mystery to scientists, until now.
For the first time, a new study in Proceedings of the National Academies of Sciences was able to pinpoint the date and likely cause of the demise of these giant animals.
After looking at sediment cores from Lake Hill — a small freshwater lake located toward the middle of the island — mammoth DNA, fungal spores, and climate “proxies” (such as pollen or microfossils), the researchers were able to figure out that the island’s mammoths most likely ran out of fresh water after a series of environmental changes.
For a few thousand of years before their extinction, a changing climate had caused sea levels to rise. This resulted in the island’s size being drastically diminished to just 42 square miles in size. At the same time, a drier climate on the island caused lakes — notably Lake Hill — to start to dry up. So about 7,800 years ago, the lake had become smaller, shallower and what water was left was likely of poor quality.
The researchers think that mammoths needed to drink about the same amount of water as modern day elephants, which is between 70 – 200 litres (approximately 18 – 52 gallons), according to the BBC.
So, as water became scarcer, the animals started to congregate around the limited water holes. This made the situation worse as the aggregation of mammoths most likely destroyed vegetation on the lake shores, causing more soil erosion and infilling of the lakes.
“The mammoths were contributing to their own demise,” Russell Graham from Pennsylvania State University told the BBC. And eventually, the mammoth populations diminished so much that the species simply died out.
According to the study, a similar scenario may also have played out for other straggler populations, including those on Wrangle Island, off the north coast of Siberia.
And these climate changes are strikingly similar to those that we face today. The researchers told Gizmodo that the extinction of these mammoths could be a cautionary tale for today, as sea levels are also rising, islands are shrinking, and freshwater levels are decreasing.