Red squirrels are rapidly evolving in response to global warming - they are the first mammals in which such genetic changes have been seen. The discovery could bode well for other species struggling to adapt to new conditions, say researchers.

Andrew McAdam, at the University of Alberta, Canada, and colleagues monitored four generations of squirrels in the Yukon, Canada, over 10 years. They found that female squirrels now give birth on average 18 days earlier in the year than their great-grandmothers.

The driving force behind the evolutionary changes is that the warmer climate means that females with a genetic propensity to give birth earlier are more likely to have offspring that prosper.

These early-borns have a head start on their younger peers. They are bigger and more independent when autumn comes and it is time to store food, says Stan Boutin, another member of the team.

The work joins a growing body of evidence that many living things are changing their abundance, distribution and behaviour in response to increasing global temperatures. Genetic changes have been shown in American mosquitoes but this is the first study that demonstrates a genetic shift in a mammal.