Here's How These Adorable Mice Can Live at an Extremely High Elevation Where No Other Mammal Is Known to Reside

A tiny rodent native to South America's high peaks has been found to carry physiological traits that let it thrive where almost nothing else with fur and a heartbeat can survive. According to a study published July 9 in the journal Science, the Andean leaf-eared mouse has evolved internal mechanisms that allow it to produce heat efficiently even when oxygen is scarce and temperatures plunge far below freezing, conditions typical of elevations near 22,000 feet.

Researchers examined how the animal's body converts energy into warmth in an environment that would overwhelm most mammals, whose lungs and blood struggle to extract enough oxygen as altitude climbs. The mouse appears to have tuned its internal chemistry specifically to keep generating body heat without the extra oxygen most species would need to do so. What remains unexplained, according to the scientists behind the paper, is why the animal made its way to such a punishing habitat in the first place, or how it got there.

Before this rodent entered the picture, biologists generally credited a different animal with the title of world's highest-living mammal. Large-eared pikas, small relatives of rabbits found across the Himalayas, had long been recorded at elevations approaching roughly 20,100 feet, and for a long stretch of scientific record-keeping, no mammal had been documented living any higher.

That assumption shifted in 2020, when a separate research team climbing Llullaillaco, a volcanic peak straddling the border of Argentina and Chile that rises to about 22,110 feet, discovered a live Andean leaf-eared mouse near its summit. The finding effectively rewrote the record books, establishing the species as the highest-dwelling mammal known to science and displacing the pika from a status it had held for years.

What makes the mouse even more unusual is not just its tolerance for extremes but the sheer breadth of environments it occupies. The same species can be found living comfortably at sea level and at virtually every elevation between there and the icy summit zones of the Andes, giving it a wider vertical range than any other mammal on record. That flexibility suggests the animal's adaptability is not limited to a narrow genetic toolkit suited only to thin air, but instead reflects a broader capacity to adjust to wildly different pressures, temperatures and oxygen levels.

Scientists studying extreme environments say findings like these carry weight beyond curiosity about a single rodent. Understanding how a mammal's cells and metabolism cope with low oxygen has parallels to human physiology, including how bodies respond to high-altitude stress, and could inform broader research into hypoxia tolerance. Still, researchers caution that laboratory and genetic work on the species is ongoing, and many questions about the evolutionary path that produced such an adaptable animal have yet to be answered.

Field biologists also note that confirming any mammal as a record holder for elevation is inherently difficult, since surveying summit environments is logistically demanding and animals may go undetected in prior expeditions. That leaves open the possibility that future surveys, whether of the Andean leaf-eared mouse or another high-altitude species, could once again shift the record. For now, though, the mouse's combination of heat-generating efficiency and an unmatched elevational range has secured its place as a standout example of mammalian resilience.

Source: Smithsonian Magazine