Invasive Animals

Our nation’s national parks are managed to preserve unimpaired America’s natural and cultural resources. This mission is under a deep and immediate threat as a consequence of invasive animal species.

Despite these challenges, there are bright spots where parks are managing invasive species challenges, as well as opportunities for the National Park Service (NPS) to take a lead in addressing the threat. Successfully maintaining America's treasures - the national parks - will require coordinated and innovative action to manage invasive animal species.


Top 5 Most Common Invasive Animals In the National Parks

Some invasive animals can completely reorganize an ecosystem and provide park staff with a constant challenge to manage properly under the new circumstances. In 2018, the top invasive animals reported by national parks spanned a wide variety of species.

Two chunky, dark, and glossy birds perched on a rock

Photo courtesy of Lee Karney/U.S. Fish and Wildlife Service

1. European Starling (Sturnus vulgaris)

The native range of the European Starling includes most of Europe, and large swaths of western and central Asia. It was first released in New York City’s Central Park in 1890, supposedly in order to bring all of the birds mentioned in Shakespeare’s plays to the New World. Since then, this migratory bird has spread across North America, and can now be found throughout the neighboring U.S. and southeastern Alaska. They are among the most abundant bird species found in North America, with an estimated population of over 200 million.

European Starlings have been known to take nests from other birds, preventing native species from laying eggs. They also cause harm to agriculture by eating crops and feed, causing hundreds-of-millions of dollars of damage each year. Further, starlings may carry diseases that are contagious to humans and livestock, such as salmonella. Due to their nature of creating large flocks, they also can cause a hazard near airports.

Orange feral cat with a rodent in its mouth
Cat preying on a rodent captured by wildlife camera in Montezuma Castle National Monument.

NPS photo

2. Feral cat (Felis catus)

Domesticated cats, our beloved household pets, are found throughout North America and the Pacific Islands, but they are not a naturally occurring species in the wild. They first appeared in the U.S. and its territories during European settlement in the 17th century. Although cats are often kept indoors, they sometimes escape or are released into the wild by their owners, ultimately contributing to a feral cat population through reproduction. Feral cats may look like your pet cat, but they are typically fearful of humans, and may even scratch or bite if approached.

Feral cats have significant impacts on natural environments. They kill billions of birds and small mammals in the U.S. every year, and have been identified as the major contributor to reducing bird populations. Globally, cats have been suspected in the extinction of several mammal, reptile, and bird species. Feral cats can also spread diseases to humans, such as toxoplasmosis and rabies.

Grey pigeon with blue and purple head sitting on a rock

NPS photo

3. Rock pigeon (Columba livia)

Rock pigeons, also known as rock doves, are found across the U.S., especially in cities. They were originally introduced to North America from Europe in the early 17th century. They have since escaped domestication, and can be found in all of the lower 48 states, and parts of southern Alaska, as well as Puerto Rico, the U.S. Virgin Islands, American Samoa, and Guam.

Rock pigeons are often considered a nuisance due to the large number of droppings they produce. These droppings can be damaging to infrastructure, such as buildings and bridges, and may also spread diseases and parasites to native bird species. Due to their preference for living among humans, it is quite common for people to come in contact with rock pigeons and their droppings. Additionally, rock pigeons can consume large amounts of grain in agricultural areas, and may pose a hazard to airplanes when they congregate around airports.

Small, brown bird perched on a wood post

Photo courtesy of Dr. Thomas G. Barnes/U.S. Fish and Wildlife Service

4. House sparrow (Passer domesticus)

House sparrows were introduced to the U.S. from Europe in the mid-1800s as a desirable species. They have since spread across the U.S., and are now quite common. They are often found around human habitations, as they prefer to build their nests on walls and in man-made structures.

Though these little brown birds may seem unassuming, house sparrows are known to aggressively compete with native birds for nests and cavities. They at times destroy the nests and eggs of native species, and may even kill nestlings and adult birds. House sparrows also have a tendency to nest on and in buildings, and can create fire hazards by packing nesting materials into vents and other structures. Additionally, they can be quite noisy when nesting in such close quarters with humans.

Shiny, green bug on a green leaf

Photo courtesy of Debbie Miller/USDA Forest Service via

5. Emerald ash borer (Agrilus planipennis)

The emerald ash borer is a bright green beetle that feeds on ash trees. It was first found in the U.S. near Detroit, Michigan in 2002. They are believed to have been brought to the U.S. via shipping material from Asia. The emerald ash borer has since spread to 35 states, and continues to spread west.

While the adults only feed on the foliage of ash trees, the larvae feed on the inner bark, making it impossible to transport water and nutrients throughout the tree. This ultimately results in the trees death. Tens of millions of trees have already died in the U.S. Ash trees are an important species in the U.S., as it is often planted in cities, and is used to make a number of products, including baseball bats, furniture, and flooring.

Data from national parks compiled from the 2018 Government Preformance and Results Act (GPRA).

CAB International. (2019). Invasive Species Compendium. Retrieved July 2019 from

University of Georgia, Center for Invasive Species and Ecosystem Health. (2019). EDDMapS. Retrieved July 23, 2019 from

U.S. Forest Service, and Michigan State University. (n.d.) Emerald Ash Borer Information Network. Retrieved July 22, 2019 from

Invasive Species Specialist Group. (n.d.). Global Invasive Species Database. Retrieved July 2019 from (

Linz, G.M., Homan, H.J., Gaulker, S.M., Penry, L.B., and Bleier, W.J. (2007). European Starlings: A review of an invasive species with far-reaching impacts. In G.W. Witmer, W.C. Pitt, K. A. Fagerstone (Eds.), Managing Vertebrate Invasive Species: Proceedings of an International Symposium (pp. 378-346). Fort Collins, Colorado: USDA National Wildlife Research Center Symposia.

Mayer, J.J. and P.E. Johns. (2007). Characterization of wild pig - vehicle collisions. In D.L. Nolte, W.M. Arjo, D.H. Stalman (Eds.), Proceedings of the 12th Wildlife Damage Management Conference (pp. 175-187).

NatureServe. (2019). NatureServe Explorer. Retrieved July 24, 2019 from

Cornell University Cooperative Extension and New York Sea Grant. (2019). New York Invasive Species (IS) Information. Retrieved July 10, 2019 from

Schorger, A.W. (1952). Introduction of the domestic pigeon. The Auk 69(4), 462-463.

Texas Invasive Species Institute. (2014). Texas Invasive Species Institute. Retrieved July 2019 from

The Cornell Lab of Ornithology. (2015). All About Birds. Retrieved July 2019 from

The Cornell Lab of Ornithology. (n.d.). Birds of North America. Retrieved July 22, 2019 from

The Cornell Lab of Ornithology. (n.d.). NestWatch: Managing House Sparrows and European Starlings. Retrieved July 22, 2019 from

The Wildlife Society. (2014). Feral Cats: Impacts of an Invasive Species [Fact sheet]. Bethesda, Maryland: The Wildlife Society.

U.S. Department of Agriculture, Animal and Plant Health Inspection Service. (n.d.). Emerald Ash Borer Beetle. Retrieved July 22, 2019 from

U.S. Department of Agriculture, National Invasive Species Information Center. (n.d.). National Invasive Species Information Center (NISIC). Retrieved July 2019 from

U.S. Forest Service, Invasive Species Program. (2019). Invasive Species Program. Retrieved July 2019 from (

Invasive Animal Management in National Parks

Prevention and early detection are key to effective management of invasive animal species. The longer an invasive species survives, the more expensive and more unlikely it is for parks to successfully remove that species.

Staff at all levels of the NPS work to manage invasive animals. Park and regional staff implement strategies locally to deal with invasive animals. Although there is some overlap, the Biological Resources Division generally addresses terrestrial invasive plants and animals, while the Water Resources Division addresses aquatic invasive species at the national level.

Contact the Biological Resources Division for questions on invasive animal species in national parks.

Learn more about invasive species management in parks under What We Do.

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    Last updated: August 21, 2019