Catching some rays.

Lizards love to soak up the sun. These animals are ectotherms and sunbathe to regulate their body temperature. But they also bask in the sun to spur production of vitamin D, which is important for healthy bones.

All vertebrates (animals with a backbone) can get vitamin D either from the foods they eat or by producing it in their skin with the help of sunlight. When Kristopher Karsten, a behavioral ecologist at Texas Christian University, fed chameleons a diet low in vitamin D, he found that the lizards increased their sun exposure to boost vitamin D levels. Chameleons that ate a diet high in vitamin D spent less time in the sun.

It seems that chameleons alter their basking behavior to regulate their vitamin D levels. "What surprised us was how effectively they did it," says Karsten.