More than 4,000 invasive species—usually introduced species that did not evolve in a particular area—had been established in the United States alone as of 1999. The delicate balance of nature that gave rise to unique species like the Marvelous Spatuletail of Peru and the Maui Parrotbill of Hawai'i is easily unsettled by the presence of invasive plants and animals.

Competing with native species, transmitting diseases, or even killing native species outright, invasive species also inflict huge economic losses and can harm human health. As landscapes are increasingly fragmented by people, the impacts of invasive species continue to increase.

The Colonists' Cats

The domestic cat is often a beloved pet, but it's also a major threat to birds. Introduced to the United States with European colonists, the number of domestic cats has tripled in the past 40 years.

Today, more than 100 million feral and outdoor cats function as an invasive species with enormous impacts. Every year in the United States, cats kill well over 1 billion birds. This stunning level of predation is unsustainable for many already-declining species like Least Tern and Wood Thrush.

Hawai'i's Invasive Species Crisis

Hawai'i provides a tragic example of invasive species' impact on native wildlife.

• Sheep brought for sport have decimated the trees that provide most of the sustenance for the highly endangered Palila.
• Rats that raid the nests of 'Akikiki are a major factor in that bird's spiral toward extinction.
• Introduced mosquitoes transmit avian diseases fatal to birds such as the 'I'iwi.
• Invasive verbesina can quickly cover nesting sites of Laysan Albatross (Mōlī).

Tackling the Invasive Threat

ABC is working throughout the Western Hemisphere to protect native birds from invasive species, with a special focus on keeping cats indoors. We also work hard to protect the endangered birds of Hawai'i from non-native predators, which often means fencing off habitats.