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Morphology

Across the estimated 366 species, hummingbird weights range from as small as 2 grams (0.071 oz) to as large as 20 grams (0.71 oz). They have characteristic long, narrow beaks (bills) which may be straight (of varying lengths) or highly curved. The bee hummingbird – only 6 centimetres (2.4 in) long and weighing about 2 grams (0.071 oz) – is the world's smallest bird and smallest warm-blooded vertebrate.

Hummingbirds have compact bodies with relatively long, bladelike wings having anatomical structure enabling helicopter -like flight in any direction, including the ability to hover. Particularly while hovering, the wing beats produce the humming sounds, which function to alert other birds. In some species, the tail feathers produce sounds used by males during courtship flying. Hummingbirds have extremely rapid wing-beats as high as 80 per second, supported by a high metabolic rate dependent on foraging for sugars from flower nectar.

Hummingbird legs are short with no knees, and have feet with three toes pointing forward and one backward – the hallux. The toes of hummingbirds are formed as claws with ridged inner surfaces to aid gripping onto flower stems or petals. Hummingbirds do not walk on the ground or hop like most birds, but rather shuffle laterally and use their feet to grip while perching, preening feathers, or nest-building (by females), and during fights to grab feathers of opponents.

Hummingbirds apply their legs as pistons for generating thrust upon taking flight, although the shortness of their legs provides about 20% less propulsion than assessed in other birds. During flight, hummingbird feet are tucked up under the body, enabling optimal aerodynamics and maneuverability.

Of those species that have been measured during flight, the top flight speeds of hummingbirds exceed 15 m/s (54 km/h; 34 mph). During courtship, some male species dive from 30 metres (100 ft) of height above a female at speeds around 23 m/s (83 km/h; 51 mph).

The sexes differ in feather coloration, with males having distinct brilliance and ornamentation of head, neck, wing, and breast feathers. The most typical feather ornament in males is the gorget – a bib-like iridescent neck-feather patch that changes brilliance with the viewing angle to attract females and warn male competitors away from territory.