Just below starlings, sparrows, squirrels, and cats (but not dogs?

https://kingcounty.gov/services/environment/animals-and-plants/biodiversity/threats/Invasives.aspx

Terrestrial Invasive Species

European Starling - these birds often evict cavity nesters from their nest holes. So they are impacting our woodpeckers, as well as swallows and wood ducks.

House Sparrow - these aggressive birds also evict some of our native birds, including house finches and chickadees, from their nests.

Eastern gray squirrel and fox squirrel - they out-compete native squirrels in urban areas.

Domestic cats - yes, the family cat, when let outside to roam, contributes to a significant loss of biodiversity among our native birds. Each year, across the U.S. it is estimated that 4 million birds are killed by cats. It is most often our native birds that become prey to these very much non-native cats. If only we could get the pet cats to focus on the invasive birds...but it doesn't work that way. Read more on our birds page.

Humans (Homo sapiens) - Read about our role as invasive species from the Introduced Species Summary Project out of from Columbia University. Here's an excerpt: "Through intelligence and technology, has successfully eliminated threat by all natural predators (large carnivores), other than disease. Impacts all stages of the ecosystem in countless ways via agriculture, water use and redirection, airborne pollutants, etc."