Skip to content. Skip to navigation

State of the Birds Report

Document Actions

Invasive & Problem Species

Photo by Marge Gibson,
courtesy of USFWS

Invasive species are those that spread uncontrollably after being introduced to an area where they are not native. Invasive plants and animals are major threats to native bird species in numerous ways.

Nonnative predators have the greatest single impact by killing adult birds as well as eggs and young. Domestic and feral cats kill hundreds of millions of birds each year. Island nesting birds, particularly seabirds, are very vulnerable since they mostly nest on the ground or in burrows and are easily captured by rats, foxes, cats, dogs, and mongooses.

Invasive plants also impact birds by rendering the habitat unsuitable. Because of the aggressive shrub saltcedar, areas along southwestern waterways have become extremely poor habitat for Willow Flycatcher, Yellow-billed Cuckoo, and other species. Saltcedar has also crowded out beaches needed by nesting Snowy Plovers. Cheatgrass has modified millions of acres of sagebrush habitat, lowering its value for species of concern such as Greater Sage-Grouse, Sage Thrasher, and Sage Sparrow.  

Introduced diseases are a major threat to some bird species. Avian malaria has contributed significantly to the decline and extinction of many Hawaiian birds, including the Kaua`i `Ō`ō. Birds on the mainland are also vulnerable to introduced diseases such as West Nile virus, which has been found in more than 200 bird species in the U.S. and which has caused significant mortality of American Crows and related species.

Many bird species have been introduced to the U.S. from other parts of the world and some have established self-sustaining populations. European Starlings and House Sparrows compete aggressively with native birds for nesting sites and frequently displace birds such as woodpeckers, swallows, and bluebirds.

Saltcedar courtesy of USDA

More Information


  • Silent Invasion: A Call to Action. October 2002. National Wildlife Refuge Association, Washington, DC. 16 pp.
  • Stein, B. A. and S. R. Flack, eds. 1996. America’s Least Wanted: Alien Species Invasions of U.S. Ecosystems. The Nature Conservancy, Arlington, VA. 31 pp.
  • Cooling the Hot Spots: Protecting America’s Birds, Wildlife, and Natural Heritage from Invasive Species. National Audubon Society, Washington, DC. 12 pp.


    Left_arrow Previous page                                                                    Next page right_arrow