Lizards may scale back head bobbing to avoid predators

Predators can really mess up a lizard’s mojo.

Male brown anoles, Anolis sagrei, tone down the swaggering head bob that says “come hither” to females and “get lost” to other males when threatening foes come along, reports biologist David Steinberg of Duke University and colleagues May 19 in the Proceedings of the National Academy of Sciences.

Steinberg’s team measured the height of anoles’ head bobs, sharp up-and-down jerks of the head, on nine tiny Bahamian islands. On five of the islands, researchers introduced carnivorous curly-tailed lizards, Leiocephalus carinatus.

On these predator-infested islands, the lanky reptiles bob their heads a lot less emphatically: a hearty nod became a timid wobble. These lizards’ biggest bobs were as little as 40 percent of those of males on non-threatened islands.

Showing off less than usual may help anoles avoid attracting unwanted attention, Steinberg and colleagues suggest.

Researchers knew that prey animals could change these types of mating and territorial signals over generations. But the idea that individual animals could tweak movement-based signals to cope with threats from predators hadn’t been well documented.