A friend of mine has a tee shirt with a picture of an earnest looking squirrel on it. The caption says, “Excuse me. Your bird feeder is empty.”

Not only are squirrels notorious for raiding bird feeders – and outwitting the humans who supply the seed – there is another way the furry tree-dwellers take advantage of their feathered neighbors. In addition to their own vigilance in scouting for danger, squirrels listen to birds to help determine if it’s safe to come down and nose about.

Bird chatter goes silent or takes on a worried, strident sound when threats are present. My family knows this. Years ago, a neighbor had a cat named Archimedes who was an indoor/outdoor sort of fellow. Without looking, we could tell when Archimedes was in their back yard because a mockingbird with babies would scold him severely.

People have long suspected that squirrels listened to bird sounds to help assess threat levels. In 2016, scientists at Oberlin College wanted to know not if alarmed birds tended to alarm squirrels – there seems to be plenty of evidence that this is so – but rather the opposite, do relaxed bird sounds make squirrels relax and behave in a less vigilant manner.

If a squirrel is nervous and concerned about danger, it stands up often, freezes often, looks up often, and may repeatedly scamper to safety. Such behavior is exhausting, and if this was all a squirrel ever did, there would be no supper and no food storage for the winter. When a squirrel feels safe, it goes quietly about the business of gathering and there is a lessening of alert behaviors.

The approached the Oberlin scientists used was to expose free-range gray squirrels to three types of recordings. One was of the screech of red-tailed hawks. Another was of ambient noise such as “wing flutter noises, sounds of small birds hopping in dry leaves, distant low-amplitude traffic and river noise, and noises associated with an adjacent building,” but with no bird calls. The third was of relaxed bird sounds with no ambient background noise. These recordings were described as “contact calls emitted by multiple individuals when not under threat of predation.” In other words, a bunch of birds twittering to each other in a carefree manner.

When hawk noises were played, squirrels went on high alert, “significantly increasing the proportion of time they spent engaged in vigilance behaviors.”

The scientists, observing from a distance, noted the level of vigilance by counting the times squirrels looked up.

They followed a hawk recording with either ambient noise or bird chatter. The number of anxious behaviors decreased slightly with the ambient noise, but decreased significantly with the bird talk.

This showed that squirrels listen to and use bird calls to help determine if it’s okay to lower the perceived threat level and get back to work.

The study was done by Marie Lilly, Emma Lucore, and Keith Tarvin and can be found by searching for a paper entitled “Eavesdropping grey squirrels infer safety from bird chatter.”

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