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Is climate change really making squirrels sleep in?

• 09 Aug 2012, 17:00
• Freya Roberts and Verity Payne

Squirrels don't often form a central part of the climate debate, and it might not be immediately obvious what a bushy-tailed rodent living on the plains of the Rockies can tell us about climate impacts.

But a new paper about the Columbian Ground Squirrel offers an interesting example of the challenges of linking local change up to global trends. The study suggests that over the past 20 years, these animals have been emerging from hibernation later, leaving them less time to eat and reproduce.

The paper suggests climate change is having an effect on the squirrels, linking their changing hibernation patterns to snow melting later in the year, which seems to be because of an increase in snowstorms towards the end of the snowy season - there was only one snowstorm after mid-April during the first decade the study considers, but seven in the second decade.

This, according to the authors, fits with climate projections that suggest the atmosphere will be able to contain more moisture as it warms, leading to more rain and snowfall. They say, citing the IPCC's 2007 report (AR4):

"Specifically, an overall increase in both total winter precipitation and the frequency of heavy precipitation events is projected"

Still snowing outside

The IPCC does suggest some regional predictions about snow and rainfall, saying:

"In southern Canada, precipitation is likely to increase in winter and spring, but decrease in summer."

Regarding snow cover, the IPCC suggests there will be shorter snow seasons on a continental scale:

"Snow season length and snow depth are very likely to decrease in most of North America..."

But as far as we can see, the IPCC report doesn't make any predictions about whether the snow will fall later in this area of the Rockies. So is the trend over the twenty year study period to later snowfall really down to climate change? It's rather hard to say.

The snow season in southern Canada does seem to be getting shorter. For example, a 2010 study comparing changes to snow seasons during the period 1989-2004 to the previous 16 years found that along the Rockies, the duration of snow season has decreased by 5-10 days, and the end of the snow season has got earlier by between 5-35 days. The paper suggests this is an indication of climate change.

But in the study area specific to the Columbian Ground squirrels, snow cover has persisted later in the year since 1992. And the authors of the new squirrel study don't draw any conclusions about whether the length of the snow season has changed over their twenty-year study period.

This might raise a question about how confidently changes in squirrel behaviour can be linked to climate change. Given that the findings of this study are so localised, and the conclusions of the IPCC are essentially on a continental scale, care should probably be taken.

It's also worth considering that these models project change over the next 100-ish years, and don't really try to look at what sort of change we are experiencing now.

Another cute animal picture? Surely not. Credit: Jeffrey Lane

Hibernation is adaptation

Whatever the cause, the fact that these squirrels are emerging later has consequences for their survival. The alpine conditions these squirrels inhabit mean that they hibernate for 8-9 months of the year, with only a short active period. As the squirrels emerge later, they have less time to reproduce and eat. Without a big enough fat store, they won't survive the following winter. The authors noted that population growth is slowing.

While leading with headlines like 'Deadly lie-in for squirrels as climate change hits hibernation' might be a step too far interpreting this study, the research does add something to the climate debate. It reminds us that within a bigger picture we should expect regional variation, and that climate change might just alter the ecosystems we occupy in unexpected ways.