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California leads the United States in biodiversity, hosting 6,500 plant species, 68 amphibians, 100 reptiles, 429 birds, 185 mammals, and more than 27,000 terrestrial invertebrates.
Its diverse geography—from Pacific coastlines to high mountain ranges and arid deserts—creates five distinct climate zones: Desert, Cool Interior, Highland, Steppe, and Mediterranean. The state also contains the nation’s highest and lowest points, and is home to the tallest, largest, and oldest trees in the world, including the world’s hottest recorded location.
Protecting this rich tapestry of wildlife is an immense challenge, and history reminds us of the cost. The iconic California grizzly bear, once emblazoned on the state flag, vanished in the 1920s. Today, many of California’s unique species face similar threats.
In November 2024, TotalVet analyzed data from the U.S. Fish & Wildlife Service’s Environmental Conservation Online System and identified the top 10 U.S. states with the greatest number of endangered species. California topped the list with 74 species currently listed as endangered, including several endemic taxa such as the San Joaquin kit fox and the salt‑marsh harvest mouse (red‑bellied harvest mouse).
Invasive species are a major driver of this crisis. Non‑native organisms outcompete native flora and fauna, deplete resources, and often irrevocably alter ecosystems. While many species have been extirpated or are in crisis, invasive species represent only one factor behind California’s endangered status.
California faces a range of threats that push species toward extinction. The U.S. Geological Survey defines an endangered species as one in danger of extinction across all or a substantial portion of its range, while a threatened species is likely to become endangered soon.
In the Golden State, hundreds of animals are labeled threatened or endangered. The U.S. Fish & Wildlife Service Environmental Conservation Online System lists 293 such species.
California hosts roughly 1,700 invasive species, draining natural habitats and imperiling native wildlife, per UC Davis research.
Climate change compounds these pressures. Environmental law professor James Salzman notes that rising sea levels and temperatures jeopardize species that have evolved for specific climates. Associate professor of ecology and evolutionary biology Morgan Tingley cites the California spotted owl, whose reliance on ancient, large trees has made its reproduction difficult under extreme drought and heavy rains, leading to its endangered status.
Urban expansion remains the principal driver behind many of California’s wildlife challenges. As housing spreads, residents introduce invasive plants, while pets disturb local ecosystems. Increased human activity also heightens wildfire risk, which destroys habitats.
Ground temperatures rise and soil fertility often declines with new developments. Building structures alter wind patterns, damaging vegetation, and urban runoff pollutes waterways.
Moreover, building more urban areas reduces natural foraging territories essential for species like the golden eagle. The National Wildlife Federation warned in 2001 that urban sprawl—defined as low-density, automobile-dependent development outside cities—was a major threat to California’s species. Recent studies, including a 2023 analysis, confirm that climate change and urbanization negatively impact Los Angeles’ bird populations.
California harbors the largest number of endemic species in the nation. Even species that are found elsewhere feel the pressure. The gray wolf, once nearly extinct in the 1920s, has made a modest comeback with nine confirmed packs, but continued support is vital.
Lange’s metalmark butterfly, endemic to California’s Antioch Dunes Refuge, saw numbers plummet from roughly 25,000 a century ago to a single-digit population of 45 in 2006 due to habitat loss. Mining and dune disruption by San Francisco expansion further reduced numbers; today, only about 150 remain.
Collectively, these challenges underscore the urgent need for robust conservation strategies to safeguard California’s extraordinary biodiversity.
