Cold, dry, oxygen-poor air defines the high Andes environment. The Llullaillaco region sits above 6,000 meters, where the landscape is so harsh that NASA once used it as a Mars training ground. Yet this rugged place, though unwelcoming for many life forms, has become a surprising refuge for others.
In a study published in Current Biology, a team of American climbers and scientists reported that the long-eared mouse, a small rodent native to the Andes, is more common in the Chilean-Argentine border zone than previously thought. Led by Jay Storz of the University of Nebraska and climber Mario Pérez, the researchers found live specimens on the summits of several volcanoes.
All collected specimens belonged to the long-eared mouse group (Phyllotis vaccarum). These mice are typically about 23 centimeters long and are known for thriving in the high Andes. Before this discovery, scientists already recognized them as hardy residents of extreme mountain habitats, but the full extent of their resilience was unclear.
Vertebrate life at these altitudes has often been described as limited. The Llullaillaco summit, rising to 6,739 meters above sea level and straddling Chile and Argentina, experiences sub-zero temperatures, virtually no rain, and oxygen levels below 44 percent. In such conditions, the long-eared mouse proved to endure and even function, emerging as the highest-altitude vertebrate recorded to date.
To understand the scope of this adaptation, the researchers expanded their fieldwork to survey 21 Andean volcanoes. Of those, 18 rose above 6,000 meters. The team recovered 13 mouse specimens that appeared to have inhabited these heights for extended periods, and in some sites there were bones and remains of other individuals nearby.
One researcher reflected on the moment: it is astonishing that a small warm-blooded mammal can survive in such an environment. The team had previously found rat remains on Andean peaks between 1970 and 1980, fueling the hypothesis that some rodents might have reached these heights as incidental visitors. Yet the new findings challenge that idea entirely.
Archaeologists have also uncovered mummified animals near ceremonial sites of the Incas on volcano rims. There has been speculation that some of these creatures were sacrificed or carried accidentally in bundles of firewood. The new data, however, makes a stronger case for natural colonization by these mice in high-altitude zones.
As Storz points out, never mind the myth that these animals arrived with ancient travelers—the evidence shows that mice reached and continue to settle at these loftier elevations on their own. The fact that trained climbers can complete a demanding ascent in a day, yet the animals seem permanently settled, suggests that the physiological tolerance of small mammals is greater than previously thought.
Further exploration is planned to uncover how these mammals survive so long in such a harsh climate. Laboratory experiments are planned to test the specific adaptations that allow them to function with limited oxygen and extreme cold. There is also evidence of microbial life at these heights, even though plants have not been observed above 6,000 meters in this region. These discoveries open the door to the possibility that other creatures may exist in the Andean highlands.
References and further reading are provided through the study team’s communications and associated scientific reports.
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