SEP 03, 2015 4:44 PM PDT

Biologist Discovers Interspecies Mimicry Of Alarm Calls

WRITTEN BY: Andrew J. Dunlop
When song birds detect a threat, they make an alarm call. Not surprisingly, when another bird hears this, they start making their own seet alarm call. Recently, University of Montana, biologist Eric Greene, who studies bird calls, discovered something quite surprising about these bird alarm calls, something no one had imagined — he realized that these bird warnings are adopted, and passed along, by completely different types of animals, animals that aren’t even birds.

Two robotic bird decoys used by biologist Erik Greene and his team to illicit warning calls in birds and other animals.

Greene explains how this works. When small bird spots a dangerous predator, a hawk or owl for example, flying toward the small bird, it warns other birds by making a soft, high-pitched seet call "It's very high frequency," Greene explains, "and it's hard to locate."

It turns out the maxim: there’s safety in numbers, applies especially to small birds. When they see a perched predator, smaller birds make another call referred to as a mobbing call. It’s an irritating sound like screeching tires. This brings other birds out of the trees to "mob" the predator and chase it away.



Greene has been watching birds do this for years, but recently, while he was watching birds do this, he noticed another creature. He noticed that squirrels seemed to be mimicking the birds’ warning calls, and adding to the alarm as soon as they heard it. Even more surprising, he found that the squirrel's mimicry is nearly perfect, even though squirrels have a very different vocal apparatus than the one birds use. 

Once he noticed this, he also realized that Chipmunks also make these calls. Greene found himself astonished by the fact that mammals and birds, species that are not even from the same order could share this early warning system.

"We've got these complex communication networks," says Greene, "and it's not just one species yakking to members of its own kind. It's all these different species — and not just birds, but mammals as well. And they're all sharing information.”

Being a scientist, Greene realized that he needed to observe and record this behavior many, many times, consistently to make sure he was interpreting it correctly. But he also knew that waiting for predators to make their appearances would take tremendous amounts of time. So, to speed up the process and provide a reliable predator to provoke the birds and squirrels in a consistent way, Greene turned to a simulacrum: a mechanical bird of prey.

In his university lab, Greene holds up a dead predator and explains, "This is going to be a robo-pygmy owl.” The terminator-like device has real feathers on the the outside, but it’s stuffed with small motors and a computer board that allow it to move. The head swivels in a very creepy way.

In the woods near Ithaca, N.Y., Greene and his team set up two of these “robo-raptors”, as Greene calls them, on artificial stumps Greene and his team can raise and lower by remote control. After the humans clear the area, and all is quiet, the research team activates the trunk. It slowly slides down, exposing the robo-raptor.

A tufted titmouse spots the “predator" first, and begins its mobbing call. Next comes a white-breasted nuthatch, who joins in. Then come house sparrows, jays and cardinals. And then, just as Greene has observed numerous times before, the squirrels begin their mobbing calls. This wall of sound, created by all of these different animals, in their way, working together, travels through the forest at 100 mph.

"It's almost as if you've got a bow wave preceding the raptor," says Greene. "In many ways, I've come to appreciate that it's hard to be a hawk. As soon as it's spotted, the alarm flies far faster through the woods than the hawk can."


Source: NPR
About the Author
  • Andrew J. Dunlop lives and writes in a little town near Boston. He's interested in space, the Earth, and the way that humans and other species live on it.
You May Also Like
DEC 09, 2019
Earth & The Environment
DEC 09, 2019
Here we go again: record level carbon emissions in 2019
A report from researchers collaborating to produce the annual Global Carbon Budget has found that 2019 will break record levels of carbon emissions…...
JAN 11, 2020
Earth & The Environment
JAN 11, 2020
The Ganges rising: water levels in the delta
A study published recently in PNAS reports the future of water-level rise in the Ganges-Brahmaputra-Meghna delta. A collaboration of researchers from the C...
JAN 15, 2020
Earth & The Environment
JAN 15, 2020
We need flexible Marine Protected Areas
The laws that apply to much of the world’s international waters are out of date – that’s why world leaders are hard at work to improve th...
JAN 26, 2020
Plants & Animals
JAN 26, 2020
The Life of an Arctic Squirrel
There is no overstating the fact that the Arctic Tundra is a cold and unforgiving place. There are few plants or animals that can survive in this extremely...
FEB 02, 2020
Plants & Animals
FEB 02, 2020
These Fish Beach Themselves When it Comes Time to Mate
Most fish probably cringe at the idea of beaching themselves on purpose, especially since they can’t breathe out of water. But this is something that...
FEB 02, 2020
Earth & The Environment
FEB 02, 2020
Land use in the tropics: what we could do better
Research published recently in the journal Nature Ecology & Evolution reports that our collective misuse of tropical lands is negatively impacting the...
Loading Comments...