While polar bears flounder in the face of shrinking ice floes, another furry creature has gotten a boost from climate change. In the past three decades yellow-bellied marmots (Marmota flaviventris) have been fruitful—and multiplied—thanks to longer summers, according to a new study.

In the Rocky Mountains, these marmots usually hibernate for seven to eight months of the year, which make the summer months "a very busy time for them," Arpat Ozgul, of the Department of Life Sciences at Imperial College London and lead author of the new paper, said in a prepared statement. "They have to eat and gain weight, get pregnant, produce offspring and get ready to hibernate again."

But as the Colorado summers have grown longer, so too has the time the marmots have to do all of these things—and do them better. This extra preparation (and reproduction) time means that "they are more likely to succeed and survive," said Ozgul, whose results were published online July 21 in the journal Nature (Scientific American is part of Nature Publishing Group).

Marmots in the Upper East River Valley in Colorado, at about three kilometers above sea level, have been trapped and tagged for research purposes at various times each summer since 1976. In those years, the two-year-old adult females were observed to have ballooned from an average August weight of 3.1 kilograms in the first half of the study to more than 3.4 kilograms in the later half of the study. And the population itself has exploded—from an average population growth of 0.56 marmots per year between 1976 and 2001 to a frisky 14.2 marmots each year from 2001 to 2008. (The researchers noted that the population increase was primarily due to better survival rates for older marmots, as marmots born earlier in the season can gain more weight before their first hibernation and have a better chance of reaching a sufficient summer weight in subsequent years.)

The marmots are not yet changing genetically, however, explained Marcel Visser, of the Netherlands Institute of Ecology (who was not involved in the study), in an accompanying essay published in the same issue of Nature. The alterations so far are "likely due to phenotypic plasticity," he wrote.

Visser also noted that the marmots' rapid growth since 2000 has paralleled a regional decline in tall bluebells (Mertensia ciliata), a key component of the animals' diet. Doing without the plant and any key compound that it might provide could mean the marmots would "have needed to be fatter to survive hibernation," he suggested. But the data haven't confirmed whether it was a change in the animals' diet, increase in the amount of food consumed in a summer—or both—that has lead to plumper, hardier marmots.

Although the change in the summer seasons in Colorado has been good for the marmots thus far, the researchers are not convinced that the animals are out of climate woods yet. As summers lengthen and winter snowpack decreases, the feeding seasons could ultimately get drier and less fruitful, likely decreasing the mammals' survival and size.

Sir Brian Hoskins, director of the Grantham Institute for Climate Change at Imperial College calls these growing ground squirrels "climate change 'canaries,'" which can act as "an early warning about the effects of climate change on our natural world." Other woodland creatures have not fared as well in the face of climate change. A study published earlier this year found that populations of the tenacious wolverine are declining, likely due to decreased snowpack.

To prepare for future changes, though, it is important to study both the successes and failures of species as they try to survive climate change, Tim Coulson, also of Imperial College and study coauthor, noted in a prepared statement. "If we can get better at predicting how climate change is likely to influence the natural world, perhaps we can devise ways to help species predicted to be adversely affected by our rapidly changing climate," he said.

Image of marmot pup standing courtesy of Raquel Moncius; image of marmot pup in live trap courtesy of Arpat Ozgul