By Dr. Becker
The song of the forest may be much more complex than was once realized, as researchers begin to tease out the true meanings behind bird calls and other forms of “language.”
Not only may a chickadee’s call, for instance, reveal a warning about an imminent predator, it might give clues as to the predator’s size and species. Further, it’s not only other chickadees that are taking note.
Research by Erick Greene, a professor of biology at the University of Montana, and others suggests many other birds, and even other types of animals, are likely listening in, using the tidbits of information to support their own survival. As reported by The New York Times:1
“Studies in recent years by many researchers, including Dr. Greene, have shown that animals such as birds, mammals, and even fish recognize the alarm signals of other species. Some can even eavesdrop on one another across classes. Red-breasted nuthatches listen to chickadees.
Dozens of birds listen to tufted titmice, who act like the forest’s crossing guards. Squirrels and chipmunks eavesdrop on birds, sometimes adding their own thoughts. In Africa, vervet monkeys recognize predator alarm calls by superb starlings.”
Birds May Use a ‘Bucket Brigade’ Warning System That Travels Through the Forest
Many songbirds produce “seet” calls, which are warnings that alert others when predators are nearby. Back in 2005, it was revealed that such signals may be quite complex. In the case of chickadees, which use a “chick-a-dee-dee-dee” call, the alarm may indicate how fast a predator is moving along with information on other stationary predators of different sizes nearby.2
Most of the subtle call differences cannot be heard by humans, although sometimes the number of “dees” at the end of the call changes (ranging from an additional 5 or 10 dees) depending on the threat, an alteration that you could certainly detect.3 Generally, the more dangerous the threat, the more “dees” attached to the end of their call.
It used to be thought that seet calls were only intended for birds nearby, but research by Dr. Greene revealed the calls travel quickly through the forest, ahead of a potential predator, giving birds time to hide. According to The New York Times:4
“Studying the phenomenon, he [Dr. Greene] documented a ‘distant early-warning system’ among the birds in which the alarm calls were picked up by other birds and passed through the forest at more than 100 miles per hour. Dr. Greene likened it to a bucket brigade at a fire.
The information rippled ahead of a predator minutes before it flew overhead, giving prey time to hide. Moreover, while raptors can hear well at low frequencies, they are not very good at hearing at 6 to 10 kilohertz, the higher frequency at which seet calls are produced. ‘So it’s sort of a private channel,’ he said.”
Chickadees are known to be especially in tune with potential threats, but they’re certainly not the only bird with complex communications. Ravens, for instance, actually use different calls based on how they associate with others.
The call used for strangers and rivals is harsh and unwelcoming. It is lower, louder and rougher in tone than a normal call, while bird friends are greeted with a more hospitable call.
Other Animals ‘Eavesdrop’ on the Call Channels
Not only do the bird calls reveal surprisingly complex data about threats, but other animals “eavesdrop” on the calls – and vice versa. Red-breasted nuthatches, for instance, respond to chickadee alarms.
Squirrels, too, understand many bird calls and even use a similar language to warn of flying predators, such as raptors. Certain chipmunks also respond to warning calls of the titmouse, while it’s thought that many birds respond to squirrel warning calls.5
What’s not known is just how many species of birds respond to, say, a chickadee’s calls, and if they do, how that information is used. The New York Times continued:6
“If chickadees indeed issue alarm calls that indicate the size and thus the danger of predators to them, how many other species of birds — robins, crows — hear and evaluate those alarms based on their own body size? Perhaps a big Steller’s jay hears a chickadee’s frantic alarm in the face of a little pygmy owl and says, in effect, ‘I’m not worried,’ ” Dr. Greene said.
Conversely, does the same jay hear a halfhearted chickadee alarm and suddenly perk up, understanding that this means a threat now lurks nearby for a bigger bird?”
Noise Pollution Might be Harming Bird Populations
Considering how important these acoustics are to birds’ ability to survive, it’s not surprising that nearby noise pollution, such as from roadways, could be taking a toll on bird populations.
A study by Jesse Barber, an assistant professor at Boise State University who studies animal acoustics, revealed, for instance, that birds exposed to road noise gained less weight and had worsened body condition overall.
This makes sense, since a bird must stop looking for food while it responds to threats and listens for alarm calls. If they can’t hear the calls of others around them, it means they have to take on more of that responsibility themselves, spending more time listening and less time feeding.
In fact, Dr. Barber’s research revealed areas with artificial road noise had a one-quarter decline in bird populations, and some birds avoided such areas altogether.7
It’s a fascinating area of research and one that will continue to reveal more about the complex life of birds.
More Fascinating Research Reveals the Complex Life of Birds
What we do know is that there’s far more to these creatures than initially meets the eye. For instance, some birds, such as the Western scrub jay, make unique calls when they encounter a dead bird. Jays will congregate in the area of the body and make loud, screeching calls in gatherings that last anywhere from a few seconds to a half hour.
Researchers speculate the reason for the behavior could be to warn other birds of nearby hazards, to provide safety in numbers, or perhaps to teach younger jays about dangers in their environment. Researchers from the Cornell Lab of Ornithology are also using acoustic technologies to monitor bird migration, particularly in remote sites for elusive species.
Since most songbird migrations happen at night, they can be difficult to detect, but audio recordings are revealing birds flying overhead in the darkness, giving researchers vital information about their paths over military bases, planned wind farms, and other locations. To date, recordings of more than 200 species of birds have been made, including a “Rosetta Stone” of sorts for the calls of 48 warbler species!8