Early trauma can shorten a red squirrel’s lifespan

Red squirrels living in Canada’s Yukon territory can have a pretty hard knock life. Bitterly cold winters, resource scarcity, intense competition for habitat, threats from large predators like the Canada lynx, and even take big reproductive risks for their genetic fitness. All of these stressors take their toll on these resilient rodents. Their early life struggles can also leave a lasting mark. The more challenges young red squirrels face in the year they’re born, the shorter their adult lifespan. The findings are detailed in a study published April 24 in the journal Proceedings of the Royal Society B: Biological Sciences and could have some implications for humans. 

Food booms

Red squirrels are about 11 inches long and weigh just over half a pound on average. They are known for their rust colored fur and “scolding chatter” above the trees. The new study uses data collected by the Kluane Red Squirrel Project, a multi-university long-term field study. The project has tracked and studied thousands of wild North American red squirrels in the southwestern region of the Yukon for more than 30 years that individually tags and tracks individual red squirrels to learn how they deal with all that’s thrown at them  . 

The new study analyzing the observations found that red squirrels that survive past their first year go on to live about 3.5 years on average. However, early life adversity like food scarcity can cut their life expectancy by at least 14 percent.

[Related: A Medieval strain of leprosy is infecting squirrels in the UK.]

“The ecosystem red squirrels inhabit in this region is unique,” study co-author and University of Arizona ecologist and evolutionary biologist Lauren Petrullo said in a statement. “Every three to seven years, their favorite food–seed from cones of white spruce trees–is produced in superabundance during what we call a food boom.”

The team found that even though these food booms are rare, they can interrupt some biological processes for the squirrels and help shape their lifespans.

“If a squirrel had a harsh first year of life, if they were lucky enough to experience a food boom in their second year of life, they lived just as long–if not longer–in spite of early-life adversity,” said Petrullo.

Rodents as proxies

Rodents like squirrels, rice, and mats, are often used as models for humans in a lab setting. However, the laboratory environment often has limited relevance to the bigger pictures of what is going on at an ecological and evolutionary level. 

“It can be hard to really replicate the ecological challenges that animals have evolved to cope with in a lab setting,” said Petrullo. 

Wild red squirrels can offer scientists a chance to better study the role that early-life environment plays. Petrullo and her colleagues hope that continued observations in the wild can help them learn more about the biological mechanisms that link squirrels’ early developmental conditions with their later-life survival. This could have some insights into our understanding of human resilience. 

[Related: Nature wasn’t healing: What really happened with wildlife during pandemic lockdowns.]

“Our findings in red squirrels echo what we know about how early-life adversity can shorten adult lifespan in humans and other primates,” Petrullo said. “Humans vary widely in how vulnerable or resilient they are to challenges faced during early development. Our study demonstrates that future environmental quality might be an important factor that can explain why some individuals appear to be more, or less, susceptible to the consequences of early-life adversity.” 

‘Born with a silver spoon’

While growing up as a young red squirrel in the Yukon can be quite difficult, there are some things that can go right. 

“Some red squirrels have the luck of being born into gentler early environments, akin to being born with a silver spoon,” Petrullo said. “Because of this, we’ve got this really nice individual variation in early-life environmental quality across a natural ecological environment.”
However, as global temperatures continue to climb, this environment is expected to see a good deal of change. It’s possible that food booms and other ecological patterns could change right alongside the climate and the connections between early-life experiences and lifespan could also shift. According to Petrullo, these changes could offer more insight into how animals may continue to adapt to environments that are only getting more challenging to survive in. Future study could also help scientists learn more about what environmental factors can buffer these squirrels from ongoing environmental threats.

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