Tiny bird with a long needlelike bill; hovers, flies forward and backward with a humming sound. Males: metallic green upperparts; red throat that flashes ruby red in the light but otherwise may look black; underparts whitish with dull green flanks; tail black and deeply forked. Females: metallic green upperparts; whitish underparts; sides pale buff; tail green at base, black in middle, with the three outer tail feathers white-tipped. Makes a variety of “chips,” squeals and twitters.
Similar species: Rufous hummingbird (Selasphorus rufus) is a casual migrant frequently observed in the western half of Missouri July through November. Male has rufous upperparts, greenish head, and black tips on the tail feathers; underparts are white. Female and immatures are metallic green above, throat spotted with brown and orange-red, tail rufous at base and tipped with white. Anna's hummingbird and a few other western species sometimes migrate through Missouri, too.