Chameleons Fine-tune Camouflage to Predator's Vision

Chameleons' mastery of camouflage goes further than anyone expected – it seems they can fine-tune their color changes to the visual systems of specific predators, according to research by Devi Stuart-Fox at the University of Melbourne, Australia based on studies of Smith's dwarf chameleon, which lives in South Africa.

This critically endangered chameleon can alter its color palette in milliseconds, either for camouflage or for social signaling.

The team captured eight males and eight females of the species. They placed them on a branch and presented them with realistic models of two of their biggest predators: the fiscal shrike (a bird that impales chameleons on thorns before eating them) and a venomous tree snake called the boomslang.
Using a spectrometer, the team took readings of the color shades and brightness of the background and the chameleon. Then, after the chameleon had spotted the predator and changed color, they took another set of readings.

The chameleons color-matched their backgrounds much more closely when presented with a bird than a snake, the team found.

However, when the team modeled the visual systems of both predators, they found that the chameleon still appeared better camouflaged to the snake than the bird, thanks to the snake's relatively poor color vision. In the presence of a snake, it seems, the chameleons just don't have to try as hard.

The researchers noticed that the chameleons were also consistently paler, compared with their background, when presented with the tree snake.

"This is probably because while birds usually approach from above, putting the chameleon against a dark background, snakes usually approach from below, putting it against a background of a light, bright sky," says Stuart-Fox.

Other animals can adjust their defensive behavior or appearance in response to different predators.

For instance, the ground squirrel pumps more hot, infrared emitting blood into its tail when it spots an infra-red sensing rattlesnake. But this is the first time anyone has observed an animal modifying that change to best avoid being seen.

Journal reference: Biology Letters.

Posted by Jason McManus.

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http://www.newscientist.com/article/dn13944-chameleons-finetune-camouflage-to-predators-vision.html?DCMP=ILC-hmts&nsref=news1_head_dn13944