The adult male rufous has a white breast with greenish back and crown. The back is sometimes glossed with metallic bronze-green. The pileum (the top of the head from the bill to the nape) is bronze-green, and the gorget (collar) is bright orange-red. The chin and throat is a shiny metallic scarlet color. The bill is long, straight, thin, black or dark brown in color. The feet are a dusky color. The adult female rufous has a metallic bronze-green back, and the pileum is a little duller than the male rufous. From the chin and the throat, down to the breast of the female, is a dull white color. Rufous Hummingbird has a body length of about 7.3 to 9.1 cm (2.87 to 3.58 in), and weighs around 2.8 g to 4.0 g (0.097 to 0.141 Oz). Unlike other birds that have large sound-producing muscles extending from the windpipe to the chest bone,the rufous has two sets of small vocal muscles in the trachea (Johnsgard 1983; Toops 1992; Sayre 1999).

Range mass: 2.8 to 4 g.

Average mass: 3.37 g.

Average basal metabolic rate: 0.06853 W.