The next time you’re at a park and you see a squirrel standing up and shaking its tail, look up. You might just catch a raptor flying by.
The eastern gray squirrel is a cautious creature, with its ears constantly perked and monitoring for a potential threat—be it the screech of a hawk flying above, the rapid pattering of an eager dog, or the rumbling of an oncoming car.
But that’s not all its listening for.
It turns out that when the songbirds sing, the squirrels are also listening. Or, more accurately, they’re eavesdropping on the casual “bird chatter” to gauge their own safety from potential predators nearby, according to a new study in the journal PLOS One.
Squirrels are what Keith Tarvin, a biologist at Oberlin College and Conservatory in Ohio who led the study, calls “public-information exploiters,” meaning they often take cues from other prey animals nearby. They’re not the only ones that do this. Earlier animal-behavior studies have shown that birds, mammals, and even fish and lizards can recognize the alarm signals of other species that share similar geographic locations and predators. Within the bird family, a nuthatch may tune in to the high-pitched call of a chickadee, which might also be paying attention to the panicked tweet of a tufted titmice.
Squirrels and chipmunks, meanwhile, speak bird too. The biologist Erick Greene of the University of Montana told NPR in 2015 that not only do squirrels recognize the seet and mob calls of birds (the former warn others of a predator, the latter draw a mob of birds to chase a predator away), but they can also mimic them to near perfection.
“Those alarm calls become public information out there for the taking,” Tarvin says. But with so much noise, he says, responding to every warning sound—even ones that turn out to be false alarms—can become costly for the squirrels, as it cuts into time used to feed or reproduce. So he and his team wanted to know if squirrels also listen for cues that signal to them that their surroundings are safe and predator-free. This is where the bird chatter comes in.
Tarvin and his team began their experiment by playing the squirrels in both the experimental and control groups recordings of hawks, which heightened their vigilance behavior—things such as freezing, looking up, and fleeing. After a few minutes, they played ambient noise for the squirrels in the control group. The other group was played recordings of “chatter” from birds feeding in his backyard. They then observed the squirrels for three minutes, tracking how their vigilance levels changed over time.
“We counted the number of times it would move its head really quick, [as if] scanning the environment,” he says, “or freeze, which turns out to be the most common response.” Those in the group that was played bird chatter indeed froze and looked up less frequently, and were overall quicker to return to their normal state of vigilance. To Tarvin’s team, that indicated that these safety cues can be just as important to squirrels as warning calls are, especially when it comes to survival.
The field of information exploitation is relatively new, and there are a lot of questions biologists such as Tarvin want answered. For example, he wants to know if squirrels tune in to a specific kind of chatter, or if urban noise affects how prey animals rely on alarm calls from other species. He suspects it does. “If those information exploiters tend to rely on information producers and you mask them [with noise],” he says, “they may allocate more of their own time toward self-vigilance, which leaves less time to forage and mate.”
Meanwhile, as squirrels are eavesdropping on birds, Tarvin suggests that city dwellers listen in on the furry rodents. “Next time,” he says, “pay attention to the squirrels.”
This post appears courtesy of CityLab.
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