Raven’s Breath
Photo: Doug Dance

Before I started this post on talking turtles this morning, I moseyed over to Wikipedia to see what words we use to describe acoustic communications between turtles. Dogs bark, geese hiss, tapirs whistle, giraffes bleat and most rodents squeak – at least, that’s what they do when we’re talking about them in English.

But turtles? Apparently, turtles have always been considered voiceless.

As of last year, we’ve known that some turtles use chirps, clicks, meows and clucks to communicate with one another. Just not at levels we were ever able to hear before the advent of modern sound equipment.

Yellow-Spotted Amazon River Turtle
Artist: Brin Edwards

But even among the animals that produce vocalizations we can hear, conversations take place that remain out of our range.

Giraffes don’t really bleat much, but they do communicate via low-frequency moans and grunts. Sumatran rhinos, for example, have been found to emit low frequency whistles that might travel up to 9.8 km (6.1 mi).

In terms of all we’re not hearing, it’s not a one-way street. Animals of all kinds can hear the infrasonic melody being sung by the earth’s surface and waters – migratory birds use it to navigate, homing pigeons use it to find their way back to their lofts.

Sources of infrasound signals that can be detected by the Comprehensive Nuclear-Test-Ban Treaty Organization’s listening stations.
Note that this graphic doesn’t include any of the sounds discussed here, mainly because the signals being listened for by these infrasound stations are either disaster-related or human-generated.
Graphic: Comprehensive Nuclear-Test-Ban Treaty Organization

Pulling on this thread of unheard sounds brought me to the story of some tamarin monkeys in the Central Park Zoo who were found to be whispering about a particular zoo supervisor, a person associated with unpleasant medical examinations.

The tamarins had, for a time, responded to the threat of his presence with screeches and loud vocalizations. After a while, however, researchers found that the monkeys switched to low frequency communication when the supervisor approached, as if to better discuss the real threat level and necessary response.

Golden lion tamarins
Artist: Sally Landry

I started with turtles, but all these whispering monkeys comforting one another and a soft-spoken earth put me in mind of one of my favorite films, Wim Wender’s 1987 Wings of Desire (Der Himmel über Berlin). Two angels spend immortality listening to all the unspoken thoughts of humanity, the inward whispers no one else can hear. They offer succor where they can.

But one of the angels becomes so entranced by a lonely woman that he decides to become human just so he can experience the world as humans do, from the taste of food to the emotion of love. All of which had been abstract to him, because he could only hear one kind of communication.

Listening closely, in the end, made the angels want to experience the lives of humans more closely, to protect those assigned to their care beyond offering simple words of reassurance.

Maybe listening closely will have the same effect on us?