sunset in Los Angeles

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LOS ANGELES — When you think of wildlife in Los Angeles, what comes to mind? Perhaps coyotes prowling the Hollywood Hills or red-tailed hawks soaring above the skyscrapers. But there’s a whole host of lesser-known creatures that call the city home, and some of them may surprise you. Take snails and slugs, for instance. These slimy urbanites positively revel in LA’s lush landscape, happily sliding through the moist nooks and crannies created by well-watered gardens and sprinkler systems.

Snails and slugs are just two examples of the incredible biodiversity that exists in the City of Angels, often hidden in plain sight. From the chaparral-covered hills to the concrete jungle downtown, LA is home to a dazzling array of native animal species. However, as the city has grown and developed over the years, many of these creatures have struggled to adapt to an increasingly urbanized environment.

A new study led by researchers at UCLA and LA Sanitation & Environment and published in PLOS One takes an in-depth look at which native LA species are urban-tolerant, like snails and slugs, and which prefer more natural habitats. To do this, the scientists tapped into a massive dataset from iNaturalist, a popular nature app where users snap and share photos of wildlife they encounter.

The team combed through over half a million iNaturalist records submitted by app users in Southern California between 2011 and 2021. They focused on 12 key animal groups ranging from mollusks and spiders to birds and mammals. After carefully filtering the data for accuracy with the help of taxonomic experts, the researchers were left with occurrence data for 967 unique native species.

Next came the tricky part — quantifying each species’ relationship with the urban environment. The team created a composite “urban intensity” index for the LA region based on factors like light pollution, paved surfaces, and noise levels. They then looked at how frequently each species was spotted across the spectrum from natural to highly urbanized areas. This allowed them to assign each species an “urban tolerance” score.

hawk in LA
Red-shouldered hawk (Buteo lineatus) perched on a telephone pole in urban Los Angeles. CREDIT: Nurit. D. Katz, CC-BY 4.0 (

Crunching the numbers revealed that, on average, LA’s native fauna are not big fans of city living. Most species were observed more often in areas with lower urban intensity scores. Interestingly, though, there was a lot of variation between taxonomic groups. While snails and slugs seemed to thrive in metropolitan areas, most other invertebrates, like butterflies, moths, grasshoppers, and crickets, had a strong preference for more natural habitats. Among vertebrates, mammals and reptiles tended to be the most urban-averse.

Even within these broader groupings, individual species showed very different responses to urbanization. While snails and slugs basked in the city’s wet hideaways, the greenish-blue butterfly avoided urban areas like the plague. The researchers speculate these stark differences may be linked to species’ particular traits and needs.

“Los Angeles should rightly pat itself on the back for attracting and supporting mountain lions, most notably, the late, great P-22,” says Joseph Curti, a doctoral candidate in ecology and evolutionary biology and lead author of the study, in a media release. “Our study highlights additional native species that are present within even the most urbanized areas of the city.”

Snails and slugs likely benefit from the variety of moist microhabitats people unwittingly create in cities via landscaping, whereas greenish-blue butterflies are intimately dependent on their native host plants, which are scarce in developed areas. More research is needed to untangle how species’ unique natural histories interact with the novel stressors and opportunities presented by urban environments.

Ultimately, the team aggregated their species-level scores into a “Community Urban Tolerance Index,” or CUTI for short. They calculated CUTI values for a grid of over 8,000 quarter-square-mile cells blanketing the City of Los Angeles. The idea is that CUTI provides a snapshot of how wildlife communities in different parts of the city are faring in terms of their overall affinity for, or aversion to, urban living.

As one might expect, the lowest CUTI scores, indicating the most urbanized fauna, were concentrated in LA’s dense urban core. But even in less developed areas, CUTI values suggested significant challenges for native biodiversity. Across all cells, the average CUTI was barely above 2 on a scale of 0 to 5. The researchers see this as a wake-up call that LA has a long way to go in making itself hospitable to its non-human inhabitants, even surprising city-dwellers like snails and slugs.

And that’s really the heart of why this study matters. Los Angeles has set the laudable goal of no net biodiversity loss by 2035. But to get there, the city needs a way to take the pulse of its wildlife populations and track the impact of its conservation efforts over time. The team believes their CUTI metric, fueled by the power of crowd-sourced community science data, can do just that.

As more species jostle for space in a growing LA, some will inevitably adapt while others will struggle without a helping hand. By keeping a watchful eye on CUTI and targeting improvements where they’re most needed, the hope is that the City of Angels can become a better neighbor to all of its wild residents, from butterflies to bobcats and the occasional slimy urbanite. In a world of rapid urbanization, Los Angeles’ efforts to understand and protect its native species can serve as a model for other cities looking to coexist with nature, even in the most surprising of places.

StudyFinds Editor-in-Chief Steve Fink contributed to this report.

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