Hummingbirds are birds in the family Trochilidae, and are endemic to the Americas. They can hover in mid-air by rapidly flapping their wings. They can fly backwards, and are the only group of birds able to do so.
Hummingbirds are small birds with long, thin bills. The bill, combined with an extendible tongue, allows the bird to feed upon nectar deep within flowers. The lower mandible can flex downward to create a wider bill opening; this facilitates the capture of flying insects in the mouth rather than at the tip of the bill.
Most species exhibit conspicuous sexual dimorphism, with males brightly colored and females displaying cryptic coloration. Iridescent plumage is present in both sexes of most species, with green being the most common color. Highly modified structures within certain feathers, usually concentrated on the head and breast, produce intense metallic iridescence.
Hummingbirds feed on the nectar of plants and are important pollinators, especially of deep-throated, tubular flowers. Like bees, they are able to assess the amount of sugar in the nectar they eat; they reject flower types that produce nectar which is less than 15% sugar and prefer those whose sugar content is around 25%. Nectar is a poor source of nutrients, so hummingbirds meet their needs for protein, amino acids, vitamins, minerals, etc. by preying on insects and spiders, especially when feeding young.
The two halves of a hummingbird's bill have a pronounced overlap, with the lower half (mandible) fitting tightly inside the upper half (maxilla). When hummingbirds feed on nectar, the bill is usually only opened slightly, allowing the tongue to dart out and into the interior of flowers.
Hummingbirds do not spend all day flying, as the energy costs of this would be prohibitive; the majority of their activity consists simply of sitting or perching. Hummingbirds feed in many small meals, consuming many small invertebrates and up to five times their own body weight in nectar each day. They spend an average of 10-15% of their time feeding and 75-80% sitting and digesting.