Chameleons fine-tune camouflage to predator's vision

Presented with a model of a predator bird (left), the Fiscal Shrike (Lanius collaris), chameleons (Bradypodion taeniabronchum) colour-matched their backgrounds much more closely than with a model of a snake (right). The Boomslang (Dispholidus typus) has poorer colour vision than the shrike, and therefore, it produced less vivid changes in the chameleons' camouflage. (Image: Devi Stuart-Fox)

Chameleons have a remarkable ability to camouflage, even adjusting their color in response to specific predators. Devi Stuart-Fox and her team from the University of Melbourne studied the critically endangered Smith's dwarf chameleon (Bradypodion taeniabronchum) in South Africa.

This chameleon can change its color within milliseconds for both camouflage and social signaling. The researchers captured eight males and eight females, placing them on a branch and introducing models of their main predators: the fiscal shrike, which impales chameleons before eating them, and the venomous boomslang snake. They used a spectrometer to measure color shades and brightness of both the background and the chameleons before and after the lizards spotted the models.

The findings revealed that the chameleons closely matched their backgrounds when faced with the bird, but they were still better camouflaged from the snake due to the snake's weak color vision. Interestingly, the chameleons appeared paler against the background when the boomslang was present. According to Stuart-Fox, this is likely because birds approach from above against a dark background, while snakes come from below, making the chameleons against a brighter sky.

Other animals also adapt their defense strategies based on predator type. For example, when ground squirrels detect a heat-sensing rattlesnake, they increase blood flow to their tails. This study is the first to show an animal adapting its color specifically to avoid detection.