Top 5 Common Invasive Animals

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.
single bird stands in front of tree
A European starling at Cuyahoga Valley National Park. NPS photo/Schmidt

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 it 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 more than 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.

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 they 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 they 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.
single bird stands in front of rock wall
A rock pigeon keeps watch at City of Rocks National Preserve in Idaho. NPS photo/Keck.

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 they may pose a hazard to airplanes when they congregate around airports.
single bird perches on a rock
A house sparrow perched on a stone at Tallgrass Prairie National Monument in Kansas. Photo courtesy of Macaulay Library/Lipton.

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 they 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 they 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.
close up of an emerald ash borer on a leaf
An emerald ash borer feeds on an ash leaf in USDA FS Northern Research Station. Photo by Leah Bauer.

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 it 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 tree’s 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’s often planted in cities and is used to make a number of products, including baseball bats, furniture, and flooring.

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Last updated: May 24, 2021