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.