Photo by Inklein, Wikimedia Commons
(Click on the following link to listen to an audio version of this blog … Marmots
(I discussed yellow-bellied marmots five years ago in “Signs of Spring 12” (May 17, 2018). Here is some new information!)
Yellow-bellied marmots (Marmota flaviventris) are one of the largest members of the “squirrel” family of rodents. They can be two feet long and weigh up to eleven pounds. They can live singly or in colonies of up to twenty individuals. They are abundant in the high meadows and rocky slopes of the mountains of the western United States and southwestern Canada.
When we go hiking up in the nearby high country, we inevitably come across marmots. Many have come to see people as reliable sources of food in their barren, rocky habitats and have lost all fear of humans. A few years back, when we were hiking in Rocky Mountain National Park, we saw yellow-bellied marmots at almost every turn of the trail, and they converged on us whenever we stopped for a water or snack break. I remember one of the marmots being fascinated with some dangling threads on the cuffs of Deborah’s jeans (the marmot did her best to chew the treads free) and others who tried to climb into our packs to get at our crackers and bags of peanuts and M and M’s. They were numerous and persistent!
The marmots we encountered, apparently, lived in colonial groups along the well-used trails of the park. They were obviously very accustomed to augmenting their plant based diet with anything they could glean from passing hikers. This human-augmented habitat could support a large number of marmots, and we never saw any marmot-on-marmot antagonistic behaviors even in their frenzy to grab the occasionally dropped M and M.
Photo by A. Vernon, Wikimedia Commons
Yellow-bellied marmots have built-in behavior patterns that help them to keep their population densities from exceeding the quality of their resource bases. Yearlings (right after their long (often eight months!) hibernation) leave the protection of their birth colony and set off to establish themselves in some unoccupied habitats. All male yearlings are dispersed in this way and about half of the females. The quality and quantity of food resources plays a role in exactly how many females are permitted to stay close to the birth burrow. The mortality figures for the young marmots that have to leave the home burrows are extreme: only half of the original birth cohort survives to one year of age, and the consequence of this yearling dispersal is a very high rate of predation (primarily by coyotes, black bears, badgers, American martens and golden eagles). Being a young marmot is not for the weak of heart!
At reproductive maturity (2 years of age) males will establish and protect a burrow with up to four females, and there can be up to twenty marmots living in very closely connected home burrows in an optimal habitat. These marmots display varying degrees of amicable social behaviors (social grooming, play, greeting behaviors) and, occasionally some aggressive, agonistic behaviors (dominance grooming, mounting, and even fighting).
Yellow-bellied marmots, then, have a very facultative approach to living in social groups.
There are a lot of advantages to living in a group. There are more eyes available to watch for predators, and each individual spends less of their own time on guard and more time on feeding or resting. Food resources can be more efficiently located and care of the young can be shared among the group. For many social animals, the loss of these group benefits can be devastating. Humans, baboons, macaques, dolphins and sheep all show terrible individual wear and tear when individuals live without a supportive society around them (for humans, living without social contacts is as serious a negative health factor as smoking a pack of cigarettes a day!). It is surprising, then, to find that yellow-bellied marmots actually live longer when they live solitary, less social lives.
Photo by C. Hernandez, NPS
In a paper published a few years ago (January 17, 2018) in Proceedings of the Royal Society B, Daniel Blumstein of UCLA and a group of associates determined that social interactions were actually not beneficial to yellow-bellied marmots. Blumstein’s paper indicated that yellow-bellied marmots with active social lives tend to live two years less that marmots that live a more solitary existence.
Blumstein speculates that close social interactions may facilitate the spread of diseases or may distract the marmots from their watchfulness for predators. The long hibernation period of these marmots can also be a time of high mortality and group hibernation may lead to inappropriate wakefulness and, thus, an increased risk of starvation during the long mountain winters.
Yellow-bellied marmots have, though, an extraordinarily long life span for a large rodent. In the wild, marmots live, on average, thirteen to fifteen years! A research team from UCLA, investigated some possible causes of this unusually long life span and published their findings this past spring in Nature, Ecology and Evolution (March 7, 2023).
Photo by Diliff, Wikimedia Commons
The study centered on a group of 73 female marmots. Females, as mentioned before, tend to stay around their home/hibernation burrows and, so, could be reliably observed and captured. Every two weeks in the summer for fourteen years, each of these 73 female marmots were trapped and blood samples were taken. The blood was then analyzed for epigenetic markers (DNA methylations) that are indicative of an on-going process of aging. When the marmots were up and active in their summer seasons, their rates of DNA methylation indicated a steady progression of aging. But, when these markers were measured just before and then just after hibernation, it was found that there was no DNA aging during the eight months of winter. In two-thirds of each year that these marmots are alive, then, their bodies do not age!
The physiological mechanisms for this ability to undergo suspended animation are being explored. It is possible that it could have medical applications to sustain seriously ill or severely injured patients. It is also possible that it could be used to help maintain astronauts on long distance space explorations. We’ll see how it works out. It does seem to serve the marmots very well, though!