On a recent visit to a favorite lava field in the mountains behind Sonoma, I paused beside a tree for a moment. My attention was drawn to a sudden flurry of activity as a plump blue-bellied lizard rushed up the tree beside me. Staring at me it began a strange behaviorÑwhat I can only describe as "push ups".

I have since learned this lizard is a common inhabitant of our region, the Western Fence Lizard. I have always assumed this behavior was a lizard's unfortunate lot, something caused by shortness of breath and performed as a means to increase oxygen supply. As usual, the more I learn about nature the more I realize how little I know. This behavior I have learned is the male fence lizard's territorial display, perhaps performed in my honor, just in case I might not know who was claiming that tree and the likely female fence lizard nearby.

The Western Fence Lizard, Sceloporus occidentalis, is one of the more common if less celebrated animals to share our local environment, and we are lucky for this. They belong to the Phrynosomatidae family of reptiles, which includes a number of visually sensitive and colorful lizards including the iguana. As many reptiles, they eat insects and spiders, and they in turn are food for mammals and birds. Like most large animals, they are also hosts to parasites.

As a host to parasites, the fence lizard may play one of the more significant roles in the local web of life, at least as far as humans are concerned. Fence lizards are a very common host for ticks. Perhaps because they, like all reptiles, are "cold-blooded", or lack the sophisticated thermoregulation (temperature control) advantages that mammals enjoy, fence lizards do not seem to pass on Lyme disease, a very uncomfortable disease for humans. In parts of the country where these lizards are not common, especially in the cooler, northern and eastern US, chances of contracting Lyme disease may be 25 times as high. Where more than fifty percent of ticks in those cooler regions may harbor Lyme disease, only one or two percent of them do here, thanks to the fence lizard.

Fence lizards live as long as five years or more, but less than twenty percent survive any given year. Reproduction would seem then to be a high priority for the species. After emerging in early spring, males soon begin to establish a territory, often a fence rail or rock or log with a vantage point from which he can keep watch. He will route out any competing males that he can and will perform his "push up" display in order to show off his distinguishing features, including his blue sides, to potential intruders. A female, and usually only one, is often nearby, less conspicuous than the male, and not at all aggressive. Females lay between three and fifteen leathery eggs each year, from May to July, and these hatch a few weeks later, depending on the climate.

In addition to territorial displays, a fence lizard will often scamper in and out of the sun to regulate its temperature. All this movement suggests perhaps why it is so common to see or hear a lizard around our valley. It appears that the climate is just mild enough here that even in winter a fence lizard may come out to sun itself. Certainly warm days in the late spring is the best time to spy them, the males doing push-ups and all of them scampering in and out of the sun. I suppose it should be said that humans may have some links to the reptiles.

This is a necessary action for a reptile which requires movement and energy, both an expense to the lizard that has to be weighed beside the advantages of lower overall energy needs.