Arctic ground squirrels could play a greater role in climate change than was previously thought.
Scientists have found that the animals are hastening the release of greenhouse gases from the permafrost - a vast, frozen store of carbon.
The researchers say it suggests the impact of wildlife on this area has been underplayed.
The findings are being presented at the American Geophysical Union Fall Meeting in San Francisco.
Dr Sue Natali, from Woods Hole Research Center in Massachusetts, US, said: "We know wildlife impacts vegetation, and we know vegetation impacts thaw and soil carbon.
"It certainly has a bigger impact than we've considered and it's something we will be considering more and more going into the future."
The Arctic permafrost, where deep layers of soil remain frozen all year round, covers nearly a quarter of the Northern Hemisphere and contains a great deal of carbon.
Dr Natali explained: "Carbon has been accumulating in permafrost for tens of thousands of years. The temperature is very cold, the soils are saturated, so that when plants and animals die, rather than decompose, the carbon has been slowly, slowly building up.
"Right now the carbon storage is about 1,500 petagrams (1,500 billion tonnes). To put that in perspective, that's about twice as much as is contained in the atmosphere."
The fear is that as the planet warms, the permafrost will thaw, releasing even more greenhouse gases into the atmosphere and causing temperatures to rise further still.
However, Dr Natali said that until now there had been little research into the effect that animals could have on this system.
To investigate, Dr Natali and Nigel Golden, from the University of Wisconsin, looked at ground squirrels: small, fluffy rodents that are found across the Arctic.
As part of The Polaris Project, they travelled to Siberia to study the squirrels' underground burrows.
Mr Golden said: "They are soil engineers. They break down the soil when they are digging their burrows, they mix the top layer with the bottom layer, they are bringing oxygen to the soil and they are fertilizing the soil with their urine and their faeces."
The team found that this activity meant that their burrows were warmer than the surrounding ground.
Mr Golden said: "We saw an increase in soil temperature in the soils where the arctic ground squirrels were occupying.
"This is a major component. As that permafrost begins to warm, now microbes can have access to these previously frozen carbons that were in the soil.
"And because they mix the soil layers, they are being exposed to warmer temperatures."
The team also found that the nitrogen that squirrels were adding to the ground through their waste was having an impact.
While this fertilizer can counteract greenhouse gas loss by causing plants to grow (which then soak up carbon dioxide from the atmosphere), it can also feed microbes in the soil, accelerating the amount of carbon dioxide and methane - both greenhouse gases - that are being released.
Dr Natali said: "If ground squirrels are adding nitrogen to an area - and that area doesn't have plants because they dug them up - this may result in increased loss of carbon from the system."
She concluded that squirrels were playing "a far more important role in this permafrost carbon cycle than we thought".
The team now wants to return to the area to quantify how much carbon is being unlocked by the squirrels - and to assess how other wildlife is affecting the area.
The researchers also want to assess how the thawing permafrost will impact on the squirrel populations themselves.
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