Hummingbirds are unique amongst birds because of their small size (2 - 20 g or 0.07 - 0.7 oz ).
With the exception of insects, hummingbirds have the highest metabolism rate of any animal on earth: elevated average body temperature (approx. 40° C or 104° F), rapid heart rate (up to 1,260 beats per minute), and high breathing rate.
They also have the largest brain (4.2% of the total body weight), the largest heart and the largest breast and flight muscles (30% of its total body mass) in proportion to body size than any other bird
Hummingbirds are the only living birds that can rotate its wings in a circle, allowing it to fly both forwards and backwards; fly up or down, move sideways, or hover in one spot.
Like other birds, they have no sense of smell.
Their feet are weak and are only used perching.
In the photo a White-chinned Sapphire, Hylocharis cyanus (Apodiformes - Trochilidae), a South American hummingbird species that is found in Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname and Venezuela, where it is mostly sedentary (non-migratory).