Male chameleons signal their aggressive intentions and prowess in fighting by adjusting the brightness of their skin colour.

Russell Ligon and Kevin McGraw at Arizona State University in Tempe staged fights between pairs of adult male veiled chameleons (Chamaeleo calyptratus; pictured) and used high-definition video to track how the animals' skin colour and brightness changed in 28 different patches on the body.

Individuals whose stripes brightened the most were more likely to charge another animal, while chameleons whose heads turned bright more quickly proved the most likely to win a bout.

The two signals could help male chameleons to separate a would-be combatant's motivation to fight from its ability to fight — two factors in competitive behaviour that can have different effects on the outcome of a contest.

Credit: MEGAN BEST

Biol. Lett. http://doi.org/qf9 (2013)