One of the last woolly mammoth populations died out on an island off the coast of Alaska nearly 6,000 years ago, probably because of a shrinking supply of fresh water.

Human hunting has been linked to the extinction of the species (Mammuthus primigenius), but this relict population perished without our help, according to Russell Graham of Pennsylvania State University in University Park and his colleagues. The authors examined ancient DNA, isotopes and plant and animal material in sediment cores from a lake on St Paul Island. They also studied mammoth fossils. The researchers estimate that the island's mammoths became extinct 5,600 years ago, when the island was shrinking because of sea-level rise and the lake was evaporating into a salty puddle — perhaps because of long-standing drought, or depletion by the mammoths themselves.

Freshwater scarcity could drive island extinctions more often than previously thought, the authors say — and will only increase as the climate changes.

Proc. Natl Acad. Sci. USA (2016)