Summit County Citizens Voice

Marmots are getting bigger, and there are more of them, thanks to global warming. PHOTO COURTESY U.S. GEOLOGICAL SURVEY.

Long-term studies show remarkable changes in size and population numbers

By Summit Voice

SUMMIT COUNTY — If you come across a giant marmot on your next hike, don’t be alarmed — it’s just another sign of global warming.

The study released last week by a team of researchers from the U.K. and the U.S. is the first to document that a shift in seasonal timing can cause changes in body mass and population size simultaneously.

The researchers used data going all the way back to 1962, showing that marmots are waking up earlier from hibernation, giving them more time to reproduce and gain weight before the next hibernation period. The study also shows the marmots are growing fatter and healthier as a result. Longer summers also mean that individual marmots are reproducing earlier and their offspring are more likely to survive the upcoming winter, so the marmot population is growing.

Yellow-bellied marmots are adapted to living in environments with a short summer and a long winter by hibernating for seven to eight months of the year. Failure to gain enough weight before the colder months can be life-threatening, as a marmot loses around 40 percent of its body mass during hibernation.

“Marmots are awake for only four to five months of the year. These months are a busy time for them — they have to eat and gain weight, get pregnant, produce offspring and get ready to hibernate again.

Since the summers have become longer, marmots have had more time to do all these things and grow before the upcoming winter, so they are more likely to succeed and survive,” said the study’s lead author, Dr. Arpat Ozgul, of the the Department of Life Sciences at Imperial College, London.

“We have observed changes in the body mass of individual marmots over the past 33 years and changes in their population size over the last decade, but we do not know what might happen in the future. Will populations thrive in the changing climate? We suspect that this population increase is a short-term response to the lengthening summers. We hope that by continuing this long-term study we will shed important light on the marmots’ future response to climate change,” added Dr Ozgul.

To reach their conclusions, the researchers analyzed data on body mass, survival and reproduction of female yellow-bellied marmots in the Rocky Mountains in Colorado. Every year, the researchers live-trapped marmots at each colony multiple times during the summer and individually marked them using numbered ear tags. They recorded the sex, mass and reproductive condition of each captured animal.

The results show that the average mass of adult marmots increased from 3094 grams in the first half of the study to 3433 grams in the second half. The research also shows that population growth increased from 0.56 marmots per year between 1976 and 2001 to 14.2 marmots per year between 2001 and 2008.

“The marmots have provided yet another example of how climate change can impact the natural world, said Professor Tim Coulson, another of the authors of the study. “We have shown how we can model the consequences of environmental change on wild populations. 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.”

Filed under: Summit County Colorado