The Ruby-throated Hummingbird is 7-9 cm long with an 8-11 cm wingspan, and weighs about 3 g. Adults are metallic green above and greyish white below, with near-black wings. Their bill is long, straight and very slender.
The adult male, shown in the photo, has a ruby red throat patch which may appear black in some lighting, and a dark forked tail. The female has a dark rounded tail with white tips and generally no throat patch, though she may sometimes have a light or whitish throat patch.
The male is smaller than the female, and has a slightly shorter beak. A molt of feathers occurs once per annum, and begins during the autumn migration.
(From Wikipedia, April 23, 2010)