The world's highest-dwelling mammal is not a hardy goat nor a red-blooded big cat, but a tiny species of rodent adorably called the yellow-rumped leaf-eared mouse.
Researchers from the University of Nebraska-Lincoln (UNL) have confirmed this tiny mouse (Phyllotis xanthopygus rupestris) is the world’s highest-dwelling mammal after catching a live specimen at an altitude of 6,739 meters (over 22,100 feet).
The mighty mouse was first spotted in 2013 when mountaineering researchers filmed a small rodent dart across the rocky landscape of Llullaillaco, a dormant volcano on the western edge of the Andes Mountains along the border of Argentina and Chile. In a recent trapping expedition in February 2020, the team returned to Llullaillaco and managed to catch a few live specimens of the mountaineering mice at altitudes over 5,000 meters (16,400 feet).
“I was a bit dazed and disoriented when I first reached the subject. My friend and climbing partner, Mario Perez Mamani, is the one who spotted the mouse, and it took me a while to process what he was telling me,” lead study co-author Jay Storz, associate professor at UNL's School of Biological Sciences, told IFLScience.
“I was still just trying to catch my breath!”
The highest specimen was caught on the summit of Llullaillaco at a dizzying altitude of 6,739 meters (over 22,100 feet). The researchers say their discovery clearly shows the yellow-rumped leaf-eared mouse is a record-breaking animal: the highest-dwelling mammal ever recorded. While there have been reported sightings of large-eared pikas, a small hamster-like mammal, living at close to 6,000 meters (19,685 feet) in the Himalayas, there has never been live evidence of mammals permanently dwelling at such an altitude.
Their research was recently published on the pre-print server bioRxiv, meaning the study is awaiting peer-review, but they are confident in their little record-breaker.
Conditions on the upper peaks of Llullaillaco are incredibly harsh. Not only does the species have to bare sub-zero temperatures as low as -65°C (-75°F), but they also have to deal with the desperately low oxygen levels – around 45 percent less oxygen than at sea-level – found at this altitude. Food is also extremely sparse here since this altitude is well above the tree line, meaning tree life and vegetation is nonexistent. The researchers suspect the mice might be eating a diet of insects and lichen, though this is based on assumptions and suspicion rather than observed evidence.
To dig deeper into the discovery, the team hopes to further study this species to see how it survives and thrives in this extreme environment.
“I study many different high-altitude animals, and I suspect that these mice have evolved specialized adaptations involving cardiorespiratory function and muscle metabolism,” Storz added. “I'm very excited to discover what enables these amazing Phyllotis mice to be able to survive and function at such extreme altitudes.”