Scientists Perplexed by Discovery of Mummified Mice on High Volcanoes: A Puzzling Enigma

From the peak of Volcán Salín, one of three Andean volcanoes, researchers found mummified mice. Analysis of these mummified mice, along with the capture of live ones, reveal that the rodents climbed these similar to Mars peaks by themselves and are surviving on them. This surprising discovery was credited to Jay Storz from the University of Nebraska-Lincoln.

In the driest desert on Earth, even on top of 20,000-foot volcanoes, the environment is incredibly harsh. Constant below-freezing temperatures, oxygen levels that are less than half of what's found at sea level, and gale-force winds across barren, rocky landscapes depict a challenging atmosphere.

Dating back to the 1970s and ’80s, archaeologists hypothesized that the mice found on various Andean peaks arrived there through the Incas who travelled over a thousand miles to these sacred sites. These mountain-tops served as locations for Capacocha - the special ritual of sacrificing children to the Incan gods. This led to the belief that these mice would have been either stowaways in the Incas' supplies, or part of the animal sacrifices.

Jay Storz, a Willa Cather Professor of biological sciences at the University of Nebraska-Lincoln, noted that many believed the mice were transported there since it was presumed to be uninhabitable. Nonetheless, the capture of a live leaf-eared mouse at the top of the 22,000-foot peak of Llullaillaco, on the Chile-Argentina border, caused Storz to doubt the original assumption. This mouse was the first known mammal found dwelling at such extreme altitudes.

In addition to finding more live mice, Storz and his colleagues reported finding 13 mummified leaf-eared mice across Salín, Púlar and Copiapó's three adjoining volcanoes. Each of these volcanoes extends nearly four miles above sea level.

Unique in their mummified state, investigators have compared the DNA of their cadavers to mice collected from different parts of the Atacama Desert. This comparison allowed them to trace the evolutionary history of these populations. The data indicated that these mice were likely not transplants but natural inhabitants of these extreme altitudes.

This observation, along with more captured live specimens and evidence of mouse burrows in the Puna de Atacama or the Atacama Plateau, has led to the belief that these mice aren't merely visiting, but are residing on these challenging volcanic summits.

Which is bewildering, Storz said, given that the Puna de Atacama ranks among the most inhospitable locales on the planet — one so arid, cold, and oxygen-poor that NASA has visited the Atacama to practice searching for life on Mars.

“Even at the base of the volcanoes, the mice are living in an extreme, Martian environment,” he said. “And then, on the summits of the volcanoes, it’s even more so. It feels like outer space.

“It just boggles the mind that any kind of animal, let alone a warm-blooded mammal, could be surviving and functioning in that environment. When you experience it all firsthand, it even further impresses upon you: How in God’s name is anything living up there?”

It’s one of a few questions that the researchers are continuing to pursue. Members of Storz’s lab and colleagues in Santiago, Chile, have since established colonies of leaf-eared mice collected from various altitudes. By acclimating each group to conditions that simulate the Puna de Atacama at 20,000 feet, the researchers hope to pinpoint whatever physiological adaptations are helping the rodents cope.

Even more fundamental is the question of what would drive the mice to such heights in the first place. Like most small rodents, the leaf-eared mouse — which grows to about 2 ounces — spends a fair amount of its time, energy, and attention avoiding predators. And even in the Puna de Atacama, those predators are numerous: foxes, mountain lions, smaller cats, birds of prey.

Could the dangers imposed by the Atacama summits — the near-absence of water, the seeming lack of food, the threat of freezing to death — really be worth the promise of escaping predation all together?

“Certainly, if you’re hunkering down on top of a 6,000-meter volcano, you’re at least safe from that,” Storz said. “You just have other things to worry about.

“But why they’re ascending to these extreme elevations is still a mystery.”