It's a story from nature's own Twitterverse.
Squirrels and songbirds are very different biologically, but they share some similarities. For one, they often live in the same environment and share the same predators. Whenever a red-tailed hawk gives out a shriek, squirrels will become vigilant and try to avoid running in the open. However, if the shriek is followed by the careless chirping of other birds, squirrels will become more relaxed and resume their normal behavior.
This is not at all surprising. There is a growing body of evidence showing that animals will tune into any useful environmental information, particularly signs of danger.
"Lots of animals listen in on the alarm calls of other species," Keith Tarvin, a behavioral ecologist at Oberlin College in Ohio, told NPR. "This has been found in a variety of squirrels — ground squirrels, tree squirrels. It's been found in monkeys. It's been found even in lizards."
However, it's not only signs of danger. Researchers suspected that squirrels tune in to the tweets of birds -- not for signs of danger, but for signs of safety. In order to test the hypothesis, the researchers observed the behavior of 54 wild Eastern gray squirrels (Sciurus carolinensis) in urban environments in Ohio. The team wanted to analyze how the squirrels respond to threat -- so they simulated a threat by playing a recording of the call of a red-tailed hawk (Buteo jamaicensis), a common predator of both squirrels and small birds. The call of the hawk was then followed with either a playback of generic songbird chatter or ambient sounds lacking bird calls.
After this experiment was set in place, the team monitored the behavior of each squirrel for 3 minutes. The squirrels' behavior was analyzed with a special app that logged the amount of time it spent freezing, fleeing, foraging, resting, standing, or looking up at the sky.
Squirrels that were played bird tweets were vigilant for less time, and returned to normal activity more quickly than squirrels that did not hear the bird calls after the hawk shriek. This suggests that the squirrels do indeed pick up cues from surrounding birds.
"When squirrels are hearing chatter coming from other birds, that chatter conveys a message or a cue that apparently these birds feel pretty safe," says Tarvin. "And the squirrels apparently interpret that to mean that the environment is relatively safe."
The authors conclude in the study:
"We knew that squirrels eavesdropped on the alarm calls of some bird species, but we were excited to find that they also eavesdrop on non-alarm sounds that indicate the birds feel relatively safe. Perhaps in some circumstances, cues of safety could be as important as cues of danger."
The study has been published in PLoS. doi.org/10.1371/journal.pone.0221279
