When people first settled Iceland around 1,100 years ago, the only land mammal already living there was the Arctic fox.
Every rodent now found on the island arrived later, almost certainly as stowaways on ships, so none are native. Yet only one species spread beyond human settlements, while the others stayed close to people.
Iceland today has four rodent species: the wood mouse, the house mouse, and two kinds of rat.
Genetic studies suggest the wood mouse arrived with the earliest settlers or the Vikings who came shortly after, likely from Britain. The rats came much later, with one species not confirmed as established until the 1820s.
Despite arriving around the same time as people, the wood mouse quietly went its own way.
While house mice and rats in Iceland still stick close to farms, ports and other buildings, rarely venturing far from human activity, wood mice spread out into the open countryside.
They now live across grassland, heath, mossy lava fields, gardens and sheltered ground beneath sea cliffs, feeding on seeds, berries, plants and insects depending on the season.
That independence has made the wood mouse an unusually important animal in Iceland’s ecosystem. With so few native land mammals to begin with, it has become the island’s only significant plant-eating rodent living wild in the countryside, a role it fills almost entirely on its own.
It also occasionally falls prey to the short-eared owl, which breeds in Iceland, and, more rarely, to the snowy owl, a rare resident.
Its population rises and falls sharply from year to year, but wherever the countryside offers cover and food, the wood mouse tends to be there, doing what its more building-bound relatives never managed.