Rufous Hummingbirds are smaller than Anna’s Hummingbirds. Adult male Rufous Hummingbirds have red bodies while adult male Anna’s Hummingbirds are mostly green. Juvenile and female Rufous Hummingbirds have rusty flanks while Anna’s Hummingbirds’ flanks are grayish green. Their vocalizations are also quite different. An Anna’s Hummingbird often sings a long buzzy series while Rufous Hummingbirds mainly issue short series of “tick” and “chip” calls. Anna’s Hummingbirds make a single loud whistle while diving while Rufous Hummingbirds issue a deep “je-je-je-deer” call along with popping sounds. Their combat calls, often heard at feeders, are also different. Anna’s Hummingbirds produce an emphatic “zeega zeega zeega!” while Rufous Hummingbirds issue a series that sounds like “zee zikiti zikiti” or “zee zee-kik.”