Q: Is there a way to tell the difference between male vs female lizards? How do they attract their mates? [Saundra, Concord]
A: One way, Saundra, is to wait until spring and watch them mate: The male is on top. But I bet you want more details than that.
The Bay Area’s most common lizard (and reptile) is the western fence lizard, aka the bluebelly. We also have sagebrush lizards, northern alligator lizards, southern alligator lizards, western skinks, Gilbert’s skinks, western whiptails, coast horned lizards, and California legless lizards. Of all these, only the fence lizard is easily identified by gender. Luckily, almost every lizard you’re likely to notice will be a western fence lizard. So the odds are with you.
Lizards and birds are evolutionarily related and resemble each other in many ways. In both, the males tend to be more brightly colored than the females: Male western fence lizards have metallic blue undersides with a dark median stripe, brilliant blue throats, bright yellow or orange coloration under the rear limbs, and large femoral glands (scent glands on the thighs). Males are more swollen at the base of the tail than females and have a pair of enlarged scales near their vent (cloaca). Females and juveniles have some color, but not nearly as bright.
Even if you can’t get a look at the lizard’s belly, there are also behavior clues that help reveal gender. As with birds, the males tend to be more aggressive and demonstrative. And although you’ll often see both males and females doing push-ups (to regulate body temperature), the males are much more energetic.
Push-ups have several purposes, including courtship. Breeding occurs mostly in the spring or early summer and is stimulated by an increase in day length. An irresistible aside: Lizards have a remarkable organ that birds do not, the parietal eye or third eye. You can see this tiny “eye” on the middle top of a bluebelly’s head—a magnifying glass helps (as does a gentle hand). This organ transmits information to the lizard’s brain, controlling body temperature and circadian (daily) rhythms. It measures the duration of light through the year, causing a reactivation of the lizard’s reproductive system in spring. Yahoo!
Push-ups (you thought I’d never get back to them!) during the breeding season mostly demonstrate fitness by revealing the animal’s brilliant colors, which are indicative of good health, notably low parasite loads. Lizards (and birds) laden with internal pathogens tend to be duller-hued. Males use both physical displays and bright colors to drive off rivals and attract the opposite sex. This also occasionally works at the local gym for humans (so I’m told).