|Male flying in California, USA|
Anna's Hummingbird is 3.9 to 4.3 inches (10 to 11 centimeters) long. It has a bronze-green back, a pale grey chest and belly, and green flanks. Its bill is long, straight and slender. The adult male has an iridescent crimson-red crown and throat, and a dark, slightly forked tail. Anna's is the only North American hummingbird species with a red crown. Females and juveniles have a green crown, a grey throat with some red markings, a grey chest and belly, and a dark, rounded tail with white tips on the outer feathers.
These birds feed on nectar from flowers using a long extendable tongue. They also consume small insects caught in flight. A PBS documentary that first aired January 10, 2010, shows how Anna's Hummingbirds eat flying insects (at 16:45). They aim for the flying insect, then open their beaks very wide. That technique has a greater success rate than trying to aim the end of a long beak at the insect.
A recent study  found that the Anna's hummingbird can shake their bodies 55 times per second while in flight. This shimmy, when done in dry weather, can shake off pollen or dirt from their feathers similar to how a wet shake by a dog removes water. This rate of shaking is the fastest of any vertebrate on earth.
Open-wooded or shrubby areas and mountain meadows along the Pacific coast from British Columbia to Arizona make up C. anna's breeding habitat. The female raises the young without the assistance of the male. The female bird builds a large nest in a shrub or tree, or in vines or on wires. The round, 3.8-to-5.1-centimetre (1.50 to 2.01 in) diameter nest is built of very small twigs, lichen and other mosses, and often lined with downy feathers or animal hair. The nest materials are bound together with spider silk or other sticky materials. They are known to nest early as mid-December and as late as June.
Unlike most hummingbirds, the male Anna's Hummingbird sings during courtship. The song is thin and squeaky. During the breeding season, males can be observed performing a remarkable display, called a display dive, on their territories. The males also use the dive display to drive away rivals or intruders of other species. When a female flies onto a male's territory, he rises up approximately 30 metres (98 ft) before diving over the recipient. As he approaches the bottom of the dive the males reach an average speed of 27 m/s, which is 385 body lengths per second. At the bottom of the dive the male travels 23 metres per second (51 mph), and produces a loud sound described by some as an "explosive squeak" with his outer tail-feathers.
Anna's Hummingbirds will sometimes hybridize with other species, but this is not very common. These natural hybrids have been mistaken for new species. A bird, allegedly collected in Bolaños, Mexico, was described and named Selasphorus floresii (Gould, 1861), or Floresi's Hummingbird. Several more specimens were collected in California over a long period, and the species was considered extremely rare. It was later determined that the specimens were the hybrid offspring of an Anna's Hummingbird and an Allen's Hummingbird. A single bird collected in Santa Barbara, California, was described and named Trochilus violajugulum (Jeffries, 1888), or Violet-throated Hummingbird. It was later determined to be a hybrid between an Anna's Hummingbird and a Black-chinned Hummingbird.
Anna's Hummingbirds are found along the western coast of North America, from southern Canada to northern Baja California, and inland to southern Arizona. They tend to be permanent residents within their range, and are very territorial. However, birds have been spotted far outside their range in such places as southern Alaska, Saskatchewan, New York, Florida, Louisiana and Newfoundland.
Anna's hummingbirds are the only hummingbirds to spend the winter in northern climates; they are able to do this as there are enough winter flowers and feeders to support them. During cold temperatures, Anna's Hummingbirds gradually gain weight during the day as they convert sugar to fat. In addition, hummingbirds with inadequate stores of body fat or insufficient plumage are able to survive periods of sub-freezing weather by lowering their metabolic rate and entering a state of torpor.
There are an estimated 1.5 million Anna's Hummingbirds. Their population appears to be stable, and they are not considered an endangered species.
- BirdLife International (2012). "Calypte anna". IUCN Red List of Threatened Species. Version 2012.1. International Union for Conservation of Nature. Retrieved 16 July 2012.
- Williamson, Sheri (2001). A Field Guide to Hummingbirds of North America. New York, NY: Houghton Mifflin Harcourt. p. 199. ISBN 0-618-02496-4.
- Peterson, Roger Tory; Peterson, Virginia Marie (1990). Peterson's Field Guide to Western Birds. Boston: Houghton Mifflin. pp. 216–217. ISBN 0-395-51424-X.
- Study to be published in an upcoming edition of the Journal for Biomechanics of Flight
- "Hummingbird speediest shaker among vertebrates". ANI News. September 4, 2013. Retrieved July 04, 2013.
- Clark, C.J.; Feo, TJ (2008). "The Anna's hummingbird chirps with its tail: a new mechanism of sonation in birds". Proceedings of the Royal Society B 275 (1637): 955–62. doi:10.1098/rspb.2007.1619. PMC 2599939. PMID 18230592.
- Yollin, Patricia (2008-02-08). "How hummingbirds chirp: It's all in the tail". San Francisco Chronicle. Retrieved 2008-02-08.
- Palmer, T.S. (September 1928). "Notes on persons whose names appear in the nomenclature of California birds". The Condor 30 (5): 277.
- Ridgway, Robert (1892). The Humming Birds. Washington DC: Smithsonian Institution. pp. 331, 329.
- Taylor, Walter P. (1909). "An instance of hybridization in hummingbirds, with remarks on the weight of generic characters in the Trochilidae". The Auk 26 (3): 291–293. doi:10.2307/4070800.
- Ridgway, Robert (1909). "Hybridism and generic characters in the Trochilidae". The Auk 26 (4): 440–442. doi:10.2307/4071292. Retrieved 2008-11-11.
- "Unusual Hummingbird for Idaho: Anna's Hummingbird - Calypte anna". Retrieved 2008-11-12.. See distribution map on bottom of page.
- "Pacific hummingbird found in eastern NFLD". CBC News. 2011-01-24. Retrieved 2011-02-03..
- Beuchat, C.A.; Chaplin, S.B.; Morton, M.L. (1979). "Ambient temperature and the daily energetics of two species of hummingbirds, Calypte anna and Selasphorus rufus". Physiol. Zool. 52: 280–295.
- Powers, D. R. (1991). "Diurnal Variation in Mass, Metabolic Rate, and Respiratory Quotient in Anna's and Costa's Hummingbirds". Physiological Zoology 64 (3): 850–870. JSTOR 30158211.
- Russell, S.M. (1996). Anna's Hummingbird (Calypte anna). In The Birds of North America, No. 226 (A. Poole and F. Gill, eds). The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington DC
|Wikimedia Commons has media related to Anna's Hummingbird.|
- Naturesongs.com: Anna's Hummingbird
- All About Birds: Anna's Hummingbird at the Cornell Lab of Ornithology
- Anna's Hummingbirds in flight taken with high speed flash
- IndieSticks.com HD video
- Anna's Hummingbird videos on the Internet Bird Collection.
- Anna's Hummingbird nests in central CA
- Anna's Hummingbird nests in southern CA
- Anna's Hummingbirds, information on winter habitat and feeding