A meta-analysis of climate change studies has revealed an image of how animals are responding to the changing world.

Researchers from the University of Colorado at Boulder examined data from 140 studies which presented a view of how 73 North American animal species, from tiny mice and shrews to larger animals like elk and polar bears, are responding to climate change.

Christy McCain of CU-Boulder's ecology and evolutionary biology department led the research, which is published in the journal Global Change Biology.

McCain and her colleagues found that the best predictor for an animal's response to climate change is its size. For larger animals, there appears to be a 100 percent response to climate changed, whereas some smaller animals are not responding at all.

A shrew foraging on the forest floor, for instance, is 27 times less likely to respond than a moose grazing nearby.

The studies involved in the analysis assessed seven different responses to climate change: extirpation (the local extinction of a species), range contractions, range shifts, changes in abundance, seasonal responses, body size and genetic diversity.

Of the 73 species included in the study, 52 percent responded as expected to climate change, while 7 percent responded opposite to expectations. Forty-one percent had no detectable response to climate change.

In addition to body size, another predictor for response to climate change is the animal's activity. Species that are only active at night or day showed more of a reaction to climate change than animals that were active during both night and daylight hours.

"This is the first time anyone has identified specific traits that tell us which mammals are responding to climate change and which are not," McCain said. "Overall the study suggests our large, charismatic fauna -- animals like foxes, elk, reindeer and bighorn sheep -- may be at more risk from climate change. The thinking that all animals will respond similarly and uniformly to temperature change is clearly not the case."

Animals' response to climate change was more pronounced for species living in higher latitudes such as pika, polar bears and reindeer.

One reason that smaller animals were not observed responding to climate change as readily as larger ones might be because smaller animals can take advantage of micro-climates present in vegetation and soil, McCain said.

"I think the most fascinating thing about our study is that there may be certain traits like body size and activity behaviors that allow some smaller mammals to expand the range of temperature and humidity available to them," McCain said. "These areas and conditions are not available to bigger mammals that live above the vegetation and experience only ambient temperatures."

McCain said the results of the study may lead the way to better conservation strategies for North American animals.

"If we can determine which mammals are responding to climate change and the ones that are at risk of disappearing, then we can tailor conservation efforts more toward those individual species," she said. "Hopefully, this potential loss or decline of our national iconic mammals will spur more people to curb climate impacts by reducing overuse of fossil fuels."