This squirrel watches its neighbor's back

Ground squirrels have few natural defenses against predators, so they rely on an early warning system to identify threats and alert others to run for cover.

But unlike meerkats that take individual turns standing watch while the rest forage, ground squirrels found off the coast of Africa keep watch together -- a behavior called synchronous vigilance, according to a new study published in the journal Behavioral Ecology and Sociobiology.

Lead author Annemarie van der Marel, a postdoctoral researcher at the University of Cincinnati, spent three winters studying Barbary ground squirrels, an invasive species introduced to the Canary Islands from Morocco on Africa's mainland. The almond-eyed, striped rodents with bushy tails live in colonies and take shelter underground in a network of burrows like other ground squirrels.

"They're pretty cute. People had them as pets and that's how they were introduced to the Canary Islands in 1965," she said.

"I looked at whether and why they were social. I began studying the strategies for how they evade predation and increase survival. That's how I got to the question of the synchronous vigilance of the species," she said.

Prey animals such as kangaroos and wild boar also use synchronous vigilance to stay safe, van der Marel said.

Co-author Marta López Darias, a researcher with the Institute of Natural Products and Agrobiology in Spain, said the synchronized behavior increased with the size of the group, similar to observations made in other species that use this defense mechanism.

Unusual for ground squirrels, the populations found in the Canary Islands are as comfortable in the trees as on the ground, she said. They seem to prefer high vantage points such as the old rock walls above the fields and ravines where they can scan all angles of their surroundings. On the Canary Islands' Fuerteventura, the squirrels face daily threats from domestic cats and birds of prey like buzzards and common kestrels.

"When they forage, they're most vulnerable," van der Marel said. "So the squirrels have to balance the time spent foraging and being vigilant. Their main defense mechanism is being watchful and alerting other group members to escape predation."

To find food, the squirrels set out daily from their underground dens to forage for roots, seeds and fruit. Active in the day, they rely on their keen vision to detect threats from the air and land. The alarm call of a nearby squirrel will alert others and may send some running for the safety of rock piles or the nearest burrow. Often, other squirrels will join in the watchful vigil.

The animals can't look for food and be on high alert for predators at the same time. So throughout the day they stop what they're doing to scan the environment together, often from a higher vantage point, van der Marel said.

Virtually all the squirrels spend time standing watch during the day. About one-third of the time, they do so alone. But 40% of the time, they have company. And when a predator is observed, multiple squirrels stop to stand watch 60% of the time, the study found.

Researchers found that squirrels that spent more time watching still found enough food to remain in good physical condition. Likewise, their extended vigilance did not affect their overall survival rates.

"There are plentiful resources and less predation pressure, so they don't have to forage as much," she said.