How Invasives Threaten Birds
Invasive Species Threaten America's Most Imperiled Bird Populations
More than one-quarter of North American bird species are in trouble or decline. Working with other conservation organizations and using a science-based process, Audubon has identified more than 200 species of birds in America that show either significantly decreasing numbers or restricted range, or face other threats. The Audubon WatchList includes birds that are restricted in their breeding range, such as the Whiskered Auklet, Elegant Tern, and Millerbird, which are highly vulnerable to introduced invasive predators in their specialized breeding areas. Other species on the WatchList, such as Bell's Vireo, are experiencing widespread habitat loss across their range, with invasive species as a contributing factor in their decline. Others, like the Bristle-thighed Curlew, have special vulnerabilities to invasive species. The Bristle-thighed Curlew has a unique flightless molt period, which makes the species particularly vulnerable to introduced predators that can quickly capture the defenseless birds.
Invasive species are one of the most critical threats to our nation's declining birds.
Invasive species threaten more than one-third of the birds on Audubon's WatchList. WatchList species are those that face population declines, are threatened by habitat loss on their breeding or wintering grounds, or have limited geographic ranges that heighten their vulnerability to isolated disasters like severe weather or oil spills.
Invasive plants like bufflegrass, Phragmites, and salt cedar are destroying habitat needed by many of America's fastest-declining birds, including Costa's Hummingbird, Curve-billed Thrasher, Seaside Sparrow, Abert's Towhee, and the Elf Owl.
The Willapa Bay area along the southwestern coast of Washington contains rich intertidal mudflats and native salt marsh habitats that make it one of the most important stopover sites on the West Coast for Dunlins, Short-billed Dowitchers, and other shorebirds. In the past decade, an invasive weed called smooth cordgrass has destroyed more than 18,000 acres of the Bay's intertidal mudflats and salt marshes.
Another WatchList species, the Long-billed Curlew, has been declining significantly over the past 150 years largely due to the disappearance of much of its prairie and meadow habitat. On San Luis National Wildlife Refuge in California, an invasive plant called yellow starthistle is wiping out grasslands and rendering the area unusable for breeding by the curlews.
For more information about Willapa Bay and San Luis National Wildlife Refuge, check out Audubon's report Cooling the Hot Spots.
Invasive species are a leading cause of bird extinctions
Invasive species have entirely or partially caused the majority of all bird extinctions since 1800. Many of these extinctions were of island birds lacking natural defenses against introduced predators. For example, invasive brown tree snakes, which arrived in Guam after World War II as stowaways on cargo ships, have decimated Guam's native forest birds. The birds of Guam evolved in the absence of snake predators, making them easy prey for the tree snakes, which are skilled climbers with a voracious appetite for eggs, chicks, and small birds. Because of the brown tree snake, nine of the 11 species of native forest-dwelling birds have been extirpated on Guam. Five subspecies of forest birds were driven to extinction, such as the Rufous Fantail and Guam Flycatcher.