A combination of song duetting and wing movements might be used by magpie-larks (Grallina cyanoleuca) to intimidate threats to their territory.
A common sight around towns and cities on the Australian mainland, the bird is known by many nicknames (mudlark, pee-wee and Murray magpie among them), and despite being black and white in appearance, is part of the monarch (Monarchidae) family of birds.
That means – in a quirk of nomenclature that you can keep in mind for your next quiz night – it is neither a magpie (Corvidae) nor a lark (Alaudidae).
These funny little birds also dress differently – males have black throats and a black ‘eyemask’ appearance, while females have white throats and less extensive black markings on the head.
And they sing together – they’re renowned for their duets that are used as a means of marking territory.
Now, it seems, these ubiquitous Australian chirpers also flap their wings mid-duet to helpfully show enemies that they mean business.
Robots are the answer to magpie-lark threat tactics
To learn this, Dr Paweł Ręk from Adam Mickiewicz University, Poland, and Professor Rob Magrath from the Australian National University recorded magpie-lark calls and created lifelike robotic models for each sex.
Using a single live male as the test subject, experiments were performed whereby speakers (playing song recordings) and robots were positioned in four combination sets.
In some tests, the male subject would see the flapping robots in front of him, with recordings played either at the robot site or separated, so as to be heard by the subject at angles.
In others, the male and female robots were separated at angles, with the recordings played either in front of the subject, or aligned to the robots.
By doing this, the researchers were able to observe the live male’s response and determined wing movements and dueting sound work in combination to frighten enemies.
“The exciting thing with the experiment was the ability to have the models and speakers in different places, allowing us to test how wing motion affected sound perception,” explains Ręk, whose research with Macgarth was published in the Proceedings of the Royal Society B.
“When the two speakers were placed apart, we found it created a less effective signal than if the speakers were together.
“However, with the speakers still apart but the robotic birds together, the wing movement created a stronger response by the listeners – as if the callers were actually close together.”
Observers piece sound and sight together
In reality, it can be difficult for a subject to determine the source of a sound, thanks to other factors like background noise and echoing.
This experiment shows the paired magpie-larks use their wing movement to make it clear to an observer that it’s them making the noise – so watch out!
As Magrath explains, it’s a bit like a human watching the telly.
“If you’re watching TV, you see someone opening and closing their mouth, and you hear the sound of their voice from a nearby speaker, your brain then constructs an illusion where the sound is coming from that person’s mouth,” Magrath explains.
“We think that magpie-larks moving their wings up and down creates a similar illusion, and acts as a way of enhancing the duet.
“In the real world, background noise and echoes can make it difficult to tell where calls come from, so the wing-waving display helps confirm when birds are together.
“Vocal duets are also more effective if the callers are close together, as they are perceived as a threatening and united team.”
Matthew Agius is a science writer for Cosmos Magazine.
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