Cassin's kingbird (Tyrannus vociferans) is a large tyrant flycatcher native to western North America. The name of this bird commemorates the American ornithologist John Cassin.
Cassin's kingbird and the western kingbird are similar in appearance. Cassin's is a little larger than the western and the upper parts are a darker gray than the western. The most distinctive difference between these birds is that the Cassin's has a thin white edge along the distal end of the tail feathers, while the western kingbird has a thin white edge that runs along the side of the tail feathers.