Territorial Red Squirrels May Live Longer If They’re Friendly With Neighbors

This photo shows a red squirrel on the lookout for territory intruders. (Credit: Erin Siracusa)

(CN) — As neighbors go, the devil you know may be better than the one you don’t.

Take the North American red squirrel, a solitary and territorial creature that is one of three species of tree squirrels. Also called chickarees, red squirrels are larger than chipmunks and defend their year-round territories fiercely.

But a new study finds that red squirrels have a higher chance of survival and more offspring when living near long-term neighboring red squirrels. For this species, the length of time the same squirrels lived next to each other increased their chance of survival, sharply offsetting the effects of aging.

“Red squirrels live on their individual territory, and they rarely come into physical contact with one another, but given the value of familiar neighbors, our study raises this really interesting possibility that they might cooperate with their competitors,” said study author Erin Siracusa, a postdoctoral researcher at the University of Exeter, in a statement

“I would argue based on our findings that despite their solitary nature, red squirrels do engage in social interactions and can have important social relationships.”

Researchers of the study, which was published Thursday in the journal Current Biology, are unsure about the nature of this cooperation among red squirrels, whether it’s sharing of food resources or actively alarm-calling to warn neighbors of predators, similar to prairie dogs. It might even include the formation of coalitions to protect neighboring territories from invaders.

Utilizing research data from the Kluane Red Squirrel Project, Siracusa and her colleagues from the University of Guelph, the University of Alberta, the University of Saskatchewan, and the University of Michigan followed 1,009 individuals over 22 years. Each summer, they gave the squirrel in the study colored ear tags so researchers could track where the red squirrels lived and with whom they shared territory boundaries.

Specifically, Siracusa focused on how social relationships affect solitary, territorial species that rarely have physical interactions with their own kind. Part of the way that red squirrels establish stable relationships is through vocalizing defensive calls known as “rattles” that identify each squirrel to their neighbors. 

Such relationships made the otherwise quarrelsome squirrels less likely to intrude on another’s territory and steal their cache of pine nuts stored for long winters.

“Once they live next to each other long enough to agree on these territory boundaries, they sort of enter into this gentleman’s agreement, saying, ‘Okay, we’ve established these territory boundaries. We know where they are. We’re not going to waste our time and energy fighting over these boundaries anymore,’” Siracusa said.

Known as the “dear enemy” phenomenon, this reduced aggression in familiar neighbors has been established in numerous species, though researchers have been unable to link such circumstances to a clear advantage.

During their research, Siracusa and her team were surprised to discover that for red squirrels, living near relatives provided no biological benefits, such as increased survival rates or reproductive advantages. 

However, the longer squirrels lived near each other, the more likely they were to survive into the next year and produce more offspring, regardless of relatedness.

“The benefits of familiarity were strong enough to completely offset the negative effects of aging,” Siracusa says.

For example, a four-year-old red squirrel that grows a year older has a survival probability that decreases from 68% to 59%. But if that same squirrel also maintains all of its neighbors, the probability of survival increases from 68% to 74%.

Siracusa hopes the findings increase understanding of the evolution of territorial systems, explaining such behaviors as migratory species returning to the same place year after year, sedentary species maintaining stable home ranges throughout their lifetime and animal mothers rarely giving up their territory for the sake of their offspring.

“I think there is a sort of interesting lesson here that red squirrels can teach us about the value of social relationships,” she notes. “Red squirrels don’t like their neighbors. They’re in constant competition with them for food and mates and resources. And yet, they have to get along to survive.”

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