Squirrels listen to the chatter of birds to know when a threat has passed | NOVA | PBS | NOVA

It may seem crazy. But squirrels are absolutely listening.

Researchers have known for years that squirrels can listen to the cries of other species to signal dangerous situations that they may not notice themselves. Now, a team of scientists has discovered another facet of the curious nature of these rodents: to know when a threat has passed, squirrels can also snoop in the informal conversation of birds – a clear sign that everything is good, again . the wooded neighborhood.

The study, published today in the journal PLOS ONE, suggests that, even for wildlife, the language of safety operates on a slippery scale. Rather than relying on simple absence alarm, squirrels will prick their ears presence another signal confirming that the coastline is clear – even if it involves dissecting the dialect from another species.

This rudimentary multilingualism is a testament to squirrel knowledge, which is "far more complex than people think they are," says Suzanne MacDonald, who studies animal behavior at York University in Canada, but did not participate in the study. the study. "Security is sometimes considered the default: when you do not hear that sound, it's protected. But that goes a little further … and that makes it a lot more interesting. "

Most humans may not care anymore, but squirrel meat has lost none of its appeal with the rest of the animal kingdom. Whether they cross trees or wade on manicured lawns, these rodents have many predators to fear, which means they need all the help they can to avoid becoming a lunch.

It is perhaps not surprising then that they have learned the jargon of some birds, who will scream, caw, sing or even cry out after detecting a predator on the lookout. Although these cries of alarm are probably addressed to parents feathered birds, squirrels with insightful ears were also surprised.

But a few years ago, Keith Tarvin, a behavioral ecologist at Oberlin College, began to wonder if the screams of alarm were only half of the wiretapping equation d & # 39; squirrel. "There is a lot of information in alarm calls," he says. "It appeared to us that the safety indices could be just as informative."

When a squirrel has reason to believe that a crisis is going on, he drops what he's doing and redistributes all his energy into a set of vigilant behaviors, like getting up on his / her feet posterior to scrutinize its environment, to freeze on the spot or to flee the zone of danger entirely. But staying in this stressful state is exhausting, and reduces the time and energy spent on other essential tasks such as foraging or looking for a potential partner. This means that having an obvious switch for predator monitoring could be as important as the trigger that activates it.

To explore this side of the story, Tarvin and his students, Marie Lilly and Emma Lucore, both undergraduate students in Oberlin at the time, decided to scare a squirrel cloud. Eastern Gray (Sciurus carolinensis) And then try to calm them down. On warm winter days, Lilly placed a pair of speakers on his bike and was looking for squirrels near the university campus. Once she found a potential candidate, she played a brief recording of the cries of a red-tailed hawk (Buteo jamaicensis) – a known squirrel predator – and wait for the rodent to react.

Unsurprisingly, squirrels became alert as soon as they heard the cries of the fearsome bird, showing the classic suite of vigilance behaviors. Then, as the rodents began to slowly return to the baseline, Lilly played another title: the chatter of several species of songbirds, chatting as if everything was red.

These sounds are distinct from calls called "sentinels" or "clear calls," vocalizations that have evolved to communicate the fact that a known threat has passed, Tarvin explains. Chatter, on the other hand, looks more like a blase babbling of birds that probably would not happen if the danger was near.

Hearing this soothing soundtrack seemed to speed up the return of squirrels to the usual, compared to a second group that had played a record of the only background noise, without chattering birds. The two groups of rodents were probably eventually directed to the same fate, says Tarvin. But in the aftermath of the panic, the chatter of birds could be a special event that would put a nervous squirrel at ease.

"It really adds something to [scientific] literature, "says MacDonald. "Not only [bird chatter] let's say there is no predator … he says to the squirrels, "Now you can really relax."

Of course, the timing of these events is probably much more variable under natural circumstances. After all, squirrels are not always near the birds that pull the breeze. But ambient gossip is "free public information" that anything within earshot could potentially take advantage, says Tarvin. In nature, the closest squirrels can listen to their feathered friends.

"Squirrels are incredibly successful," says Amanda Robin, a squirrel researcher at the University of California at Los Angeles, who did not participate in the study. "This could be another example of how they are able to take advantage of the elements of their environment."

We still do not know how squirrels learn to agree to avian chatter. But appeals initiated in the study covered a dozen different birds, suggesting the possibility that these rodents have the cognitive flexibility needed to decipher similar signals from a wide range of species ( including, perhaps, some of their noisiest neighbors: the man).

"It shows how interconnected ecosystems are," says Robin. "If you have deleted a species [like a bird]you could change the whole life of another species without knowing it.

Understanding these subtle ecological networks will be essential for future conservation efforts, says Lilly. With the levels of noise pollution on the rise, we humans may already be covering communications in the environment that we are not even aware of.

MacDonald agrees. "Animals do not just pay attention to other squirrels, they pay attention to everything that happens in the environment," she says. "That's why biodiversity is so important."