Animal immigrants go native in California

Hundreds of invasive animal species have established themselves in California, where many are capable of creating economic or ecological disasters. They arrived in many ways. Some were introduced as game, such as the wild turkey and the ringneck pheasant. Red fox escaped from fur farms. African clawed frogs were lab animals and pets. Green crabs are thought to have arrived in ballast water. Here are a few of the animal immigrants that have become ubiquitous in California:

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House sparrow

Range: Common throughout California in areas of human habitation.

Facts: Detrimental to many native bird species because it takes over nest sites.

How it got here: Imported from Europe to the Eastern U.S. in the 1800s; believed to have come west with the railroads. First reported in the 1870s in the San Francisco Bay Area.

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Virginia opossum

Range: Common in areas west of the Sierra in a variety of habitats including woodlands, agricultural and residential areas. Prefers areas near water sources.

Facts: Only marsupial native to North America. Not considered a threat to native species; rarely lives longer than 18 months because of predation and run-ins with vehicles.

How it got here: Believed to have been introduced in the San Jose area as a game animal (for its meat and pelt) in the late 1800s or early 1900s.

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Rock dove (common pigeon)

Range: Throughout California except at the highest elevations and in very arid regions.

Facts: Considered the No. 1 bird pest in the U.S. In captivity, pigeons can live up to 15 years, but about 30% of the wild population dies each year.

How it got here: Native to Europe and North Africa, domesticated rock doves were believed to have been brought to North America by European settlers as early as the 1600s. It is now found throughout the world.

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Bullfrog

Range: Widespread in the state near lakes, streams, irrigation ditches and ponds, except at very high elevations. It requires a permanent water source.

Facts: Believed to be driving some native frog species to extinction. The largest true frog in North America, bullfrogs prey on insects, crustaceans, snakes, birds, mice and frogs, including other bullfrogs.

How it got here: In the late 1800s to early 1900s, for their meaty legs.

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House mouse

Range: Almost anywhere there are people.

Facts: Because of its affinity for living near people, it doesn’t compete with native rodents.

How it got here: Native to Central Asia, but left the wilds to live around people with the development of agriculture and permanent settlements over 10,000 years ago. Spread with humans to much of the world.

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Parakeets and parrots

Range: Southern California, Bakersfield, San Francisco Bay Area. Common species include the rose-ringed parakeet, red crowned parakeet and mitred parakeet.

Facts: Not considered pests at this time.

How they got here: Various species from Mexico, Central and South America, India and Africa were set free into the wild through deliberate or accidental releases from homes, pet stores or aviaries.

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Sources: California Department of Fish and Game, California Parrot Project, University of Michigan Museum of Zoology, Columbia University Introduced Species Summary Project