Last updated June 28, 2018 at 9:54 am
A last chance effort to avoid being eaten.
Like the display of the Frilled Necked lizard, or the electric blue warning signal displayed by the Southern Blue Ringed Octopus, the ‘blueys’ blue tongue is what’s known in the biological world as a deimatic display. The idea goes that the surprise appearance of something big or bright (or both) on an animal causes a reflexive startle and recoil in the predator.
“Blue tongue lizards have a highly conspicuous tongue, but unlike many other kinds of lizards, it’s a big tongue—the surface area is large. When blue tongues do a ‘full tongue’ display, the mouth is opened widely and the tongue is flattened and expanded. At the same time, they may hiss and puff-up their body for maximum effect. This behaviour, in combination with a highly conspicuous tongue, can be quite intimidating for anyone that has got too close to a wild bluey,” said Associate Professor Martin Whiting from The Lizard Lab at Macquarie University.
How blue is a blue tongue?
The Lizard Lab at Macquarie University first tested to see just how blue a blue tongue is, measuring the colour by bouncing light off the lizard tongues.
“Not only are their tongues blue, but they also have a very pure UV component, and the purest or most obvious UV was also at the rear of the tongue. UV is not visible to most mammals (and therefore humans), but is visible to lizards, birds and snakes.” said Whiting.
“Given that both male and female blue tongues have UV tongues, we tested the hypothesis that the tongue colour probably evolved in response to predation pressure,” said Whiting.
Lizards flash their blue tongues as a last resort defence
To test this, the research team set up wild caught Bluetongue lizards in a test arena and introduced model predators including a frozen Western Brown snake, a stuffed kookaburra, stuffed monitor lizard, stuffed fox, or a block of wood as a control and measured the types of defensive behaviour from the lizards like tongue flicking, full tongue displays, hissing and puffing up their body to appear larger.
They found that the biggest full tongue displays occurred during the most intensive final stages of predator attacks. The timing is key – flash that blue tongue too early and the lizard risks breaking it’s camouflage and attracting unwanted attention, but leave it too late and it might not work at all.
“Blueys did not respond much to the piece of wood (control) while they showed a strong response to the model predators that would normally represent the greatest threat. By delaying their display until the predator was very close, and exposing the rear of the tongue, which has the most UV and which is the brightest, blueys maximise their chance of intimidating a predator and surviving another day,” concluded Arnaud Badiane, a PhD student on the research team.
The next step for this research will use real predators and model bluetongues. The research team are building robotic bluetongue lizards with interchangeable tongues of different colours to present it to predators like live kookaburras to confirm the anti-predator hypothesis.