U. SHEFFIELD (UK)—Longer summers brought on by climate change are giving mountain marmots an earlier wake-up call from hibernation, allowing them more time to gain weight and reproduce, according to a new study.

Details of the 33-year study appear in Nature.

Scientists from the U.K. and U.S. looked at a population of yellow-bellied marmots (Marmota flaviventris), which are large ground-dwelling animals that live at around 3000 metres in the Colorado Rocky Mountains.

The study shows that the marmots are growing fatter and healthier and that the marmot population is increasing in size.

Longer summers also mean that individual marmots are reproducing earlier and their offspring are more likely to survive the upcoming winter.

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, losing around 40 percent of its body mass.

The study, which began in 1962, focuses on the most comprehensive data collected between 1976 and 2008, and is the first study of any species to show that a shift in seasonal timing can cause changes in body mass and population size simultaneously.

Researchers analysed data on body mass, survival and reproduction of female yellow-bellied marmots in the Rocky Mountains in Colorado. Every year, the researchers individually marked marmots at each colony multiple times using numbered ear tags, recording sex, mass, and reproductive condition of each animal.

Average mass of adult marmots increased from 3094 grams in the first half of the study to 3433 grams in the second half. Population growth increased from 0.56 marmots per year between 1976 and 2001 to 14.2 marmots per year between 2001 and 2008.

“Understanding and predicting how a particular organism might respond to a rapidly changing environment presents a real challenge for scientists, not least because there are many interrelated biological processes that can be influenced by these changes,” says Dylan Childs, of the University of Sheffield’s Department of Animal and Plant Sciences.

“We’ve tackled this problem by looking in detail at historical patterns. We hope to use this approach in the future to understand how other species’ may be responding to our rapidly changing world.”

“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,” says Arpat Ozgul, lead author of the study from the Department of Life Sciences at Imperial College London. “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.

“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.”

Researchers from the University of Kansas, University of Florida, Stanford University, and the University of California-Los Angeles were coauthors on the Nature study. The work was funded by the National Science Foundation, Wellcome Trust, Natural Environment Research Council, National Institutes of Health, and the National Institute on Aging.

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