During an expedition to the high Andes in 2020, a yellow-rumped leaf-eared mouse was found on the summit of Llullaillaco, a 6,739m-high volcano straddling the border of Chile and Argentina, making it the highest-living mammal - we know about.
The species also occurs at sea level, so it is clearly highly adaptable. But writing in the journal PNAS, where they published their discovery, the biologists note that it’s far from clear what the Llullaillaco population eats at these altitudes, which are 2,000m above the range of green plants.
They are fairly large mice, weighing around 55g and it is particularly recognisable by its large ears, which are around 27mm long.
The world’s highest mountain tops are under-explored by biologists, so it’s a record that might yet be broken.
The yak is another strong contender for for highest-living mammal. These large, shaggy, mainly domesticated bovines live in the Himalaya at altitudes as extreme as 6,000m.
The animals are superbly adapted for such high lives – the combination of a dense, furry undercoat and a long, shaggy overcoat keeps out the bitter mountain chill; their limited sweat glands conserve heat; and their large lungs, together with a particularly high red-blood-cell count, retain oxygen.
Other enthusiasts for elevation include the snow leopard, which lives as high as 5,400m, also in the Himalaya; and the vicuña, the wild ancestor of the alpaca, which survives up to 5,800m in the Andes.
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Main image: an illustration of the yellow-rumped leaf-eared mouse © Bell, Thomas; Darwin, Charles; Gould, Elizabeth; Gould, John; Owen, Richard; Waterhouse, G. R., Public domain, via Wikimedia Commons