When you think of Southern California, bustling cities and sprawling suburbs likely come to mind. But amidst the concrete, glass, and steel, there’s a hidden world of wildlife quietly adapting to the rapid changes humans bring. Among the surprising survivors in this urban wilderness are creatures like the western fence lizard, seamlessly blending into the landscape. Yet, these lizards aren’t just surviving—they’re evolving right before our eyes, a living example of how urban ecology drives real-time adaptation and recent evolution.

If you live in Southern California, you’ve probably had the experience of walking out your front door and catching just the slightest flicker of movement in your peripheral vision. Your instincts kick in: something skittered, something small. You glance over and, sure enough, it’s Sceloporus occidentalis, better known as the western fence lizard.

This reptile is a regular in the California cast of critters. With its vibrant blue belly and sun-loving mien, it’s the unsung hero of our yards, patios, and hiking trails, darting from log to rock, always a step ahead. Impressively, the lizards have found a home in the urban sprawl of our cities, and new research reveals they are evolving to thrive here, adapting to the ever-changing urban landscape.

It is the males who sport vibrant patches of blue on their bellies and throats, making them easy to identify. Females, while less flashy, still have a subtle charm with their more muted tones. They are able to darken or lighten their scales in response to environmental conditions, particularly temperature. In cooler conditions, they tend to darken, which helps them absorb more heat from the sun. Conversely, in warmer conditions, they may lighten to reflect sunlight and avoid overheating. This color change is not as dramatic as in animals like chameleons, but it’s an important survival mechanism for thermoregulation.

The Western Fence Lizard has a long and fascinating evolutionary history, stretching back millions of years. They belong to the genus Sceloporus, or spiny lizards, which consists of over 90 different species, and their closest relatives include the Sagebrush Lizard and the Eastern Fence Lizard, each of which they very closely resemble. These fantastic reptiles evolved to fill a specific ecological niche, with their coloration and agility being key to their survival in the wild.

The Western Fence Lizard is a versatile tenant, thriving in a range of habitats, from coastal sage scrub and chaparral to forests and grasslands. You see them everywhere in the San Gabriel Mountains, and throughout Southern California. They’re extremely common in backyards and some of the dryer areas around Los Angeles. These lizards are known for their love of basking in the sun, which they do to thermoregulate. You’ll often find them perched on rocks, fence posts, or tree branches, soaking up rays and keeping an eye out for predators and tasty nibbles. Small crickets are one of their favorites, although they will also munch on ants, beetles, spiders, grasshoppers, and flies. In fact, having a few of them in your yard can be a somewhat effective method of pest control.

When it comes to love, the Western Fence Lizard has some fascinating rituals. The mating season, which typically spans from April to July, is when the males put on a dazzling display to attract a mate. They perform a series of push-ups, showing off their bright blue bellies and throats. Scientists believe this is both a territorial display, typically to intimidate other male lizards and asserting dominance, but also a tact to impress females, who are wooed by the workout as well as the color, and who then select the most vigorous and flashy males to father their offspring. It’s not unlike what happens on a typical summer afternoon down at Muscle Beach in Santa Monica.

Western fence lizards lay their eggs in moist soil, and after a few months, a new generation of color-changing acrobats emerges, ready to take on the world. The females dig small burrows or shallow nests in these locations, and after laying the eggs, they cover them with soil to keep them insulated and safe. I love it when this happens because very often there are a dozen or more adorable little baby lizards hanging out around the yard.

The lizards are also an excellent local example of what called urban ecology. Urban ecology is the study of the relationships between living organisms and their environment in urban areas. Numerous studies around the world have shown that the spread and growth of urban environments has caused genetic changes in various species. It’s happening here, too, with our own local flora and fauna, including the western fence lizard.

“We usually think of evolution as being this super slow process that takes millions of years to happen and that no human could ever observe,” says San Diego State University herpetologist Kinsey Brock. “But really, things can happen fast when the environment changes quickly, and if they don’t, you don’t persist.”

Recent studies have shown that western fence lizards in California are not just surviving in urban environments—they’re adapting in fascinating ways, providing a glimpse into natural selection in real-time. As cities and suburbs expand into their natural habitats, these resilient reptiles have begun to develop traits that help them thrive in the concrete jungle. Researchers have found that urban lizards are exhibiting changes in their behavior and physiology compared to their rural counterparts. For example, they tend to have reduced escape responses to humans and other urban disturbances, likely because they’ve grown accustomed to frequent interactions with people and cars. Instead of darting away at the slightest movement, urban lizards may tolerate closer proximity to humans, conserving energy for more immediate threats.

Moreover, their physical traits are also shifting in response to city life. A recent study on western fence lizards in Los Angeles reveals how urbanization is driving evolutionary changes in this species morphology. Researchers at the University of California Los Angeles (UCLA) found that urban lizards have shorter limbs and smaller toes compared to their rural counterparts. These adaptations are likely responses to navigating artificial surfaces and coping with the warmer temperatures in cities.

Another study conducted in Los Angeles found that urban western fence lizards have fewer scales than their rural counterparts, likely in response to the urban heat island effect. Lizards lose moisture through the skin between their scales, so those with many small scales have more exposed skin and greater evaporative water loss. In contrast, fewer and larger scales reduce the amount of exposed skin, minimizing water loss in the warmer urban environments. This adaptation helps urban lizards cope with the heat by retaining moisture more effectively, an essential trait for survival in cities where temperatures are often higher than in surrounding natural areas.

These changes are a testament to the flexibility of natural selection, as the urban landscape becomes a new selective pressure driving small but significant shifts in the species. It’s a remarkable example of how wildlife can adapt to human environments, and in a relatively short period of time, offering a window into how evolution can occur almost quickly even in the most unexpected places.