The Costa's Hummingbird is small with green upperparts. Males have an iridescent violet crown and throat patch, also called a gorget, which extends out the sides of the throat. Females have a white throat and underparts, sometimes with violet feathers. Juveniles resemble adult females; have a gray-buff edging on feathers of upperparts, and a doubly-rounded tail instead of singly-rounded.

References cited in Species Profile

• Baltosser, William H. and Peter E. Scott. 1996. Costa's Hummingbird (Calypte costae), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/251
• Cornell Lab of Ornithology. 2015. Costa's Hummingbird. All About Birds. http://www.allaboutbirds.org/guide/costas_hummingbird/id
• Great Basin Bird Observatory. 2015. Costa's Hummingbird. http://www.gbbo.org/pdf/bcp/51_Costas's%20Hummingbird.pdf
• Partners in Flight - U.S. 2015. Costa's Hummingbird. http://www.partnersinflight.org/WatchListNeeds/COHU.htm
• Woods, R. S. 1927. The hummingbirds of California. Auk 44:297-318.