A South American mouse is the world’s highest-dwelling mammal

A yellow-rumped leaf-eared mouse has shattered the world record as the highest-dwelling mammal yet documented.

The mouse (Phyllotis xanthopygus rupestris) was found 6,739 meters, or 22,110 feet, above sea level on the summit of Volcán Llullaillaco, a dormant volcano on the border of Chile and Argentina. For comparison, Mount Everest is 8,848 meters high (29,029 feet).

The record was previously held by the large-eared pika (Ochotona macrotis), reported at an altitude of 6,130 meters during a 1921 Mount Everest expedition. Birds have been found at even higher altitudes (SN: 2/13/14).

That mammals can live at these heights is astonishing, considering there’s only about 44 percent of the oxygen available at sea level. “It’s very difficult to sustain any kind of physical activity, or mental activity for that matter,” says Jay Storz, an evolutionary biologist at the University of Nebraska–Lincoln. The temperature is also rarely above freezing and can drop as low as –60° Celsius.

Storz and colleagues captured several yellow-rumped leaf-eared mice, including the summit-topping one, plus mice from three other species from a range of high altitudes, the team reports July 16 in Proceedings of the National Academy of Sciences. Next, the team plans to look for genetic changes that might have equipped these animals to survive at high elevations. Surprisingly, another yellow-rumped leaf-eared mouse was found at sea level, indicating that this species has the broadest altitude distribution of any mammal, in addition to the altitude record.

“It’s so amazing that they’re up there,” says Graham Scott, a physiologist at McMaster University in Hamilton, Canada who was not involved in the study. Understanding how these and other animals survive under low-oxygen conditions could provide insight into how humans could overcome diseases that cause reduced oxygen levels, he says.