What figure of speech is used by the author to describe the humming bird?

Directions: Answer the given question based on the following passage:

Central and South America have some of the world’s most unique species of wildlife. Perhaps, some are more familiar than others. Central and South America has many different groups of species, which include: mammals, birds, reptiles, amphibians, fish, and insects. These groups of animals need to live in specific types of climates and habitats in order to ensure their survivorship.

South America is the home to some of the strangest, some of the loveliest and some of the most horrifying animals in the world. There can be few creatures more improbable than the sloth which spends its life in a permanent state of mute slow motion, hanging upside down in the tall forest trees: few more bizarre than the giant ant eater of the Savannahs, its tail enlarged into a shaggy banner and its jaws elongated into a curved and toothless tube.  On the other hand, beautiful birds are so common as to become almost unremarkable. Gaudy macaws flap through the forest, their splendid plumage contrasting incongruously with their harsh cries; and humming–birds, like tiny jewels, flit from flower to flower sipping nectar, their iridescent feathers flashing the colors of the rainbow as they fly.

The Amazonian rain forest, in Brazil alone, is the largest rain forest in the world. Many species of mammals, reptiles, amphibians, insects, and birds occupy the canopy of this magnificent rain forest. The iguana lives in the trees high above from the ground. It has flattened sides and a long, strong tail, which gives it balance and stability when it leaps. It also has clawed feet, which allows the iguana to grip branches.

The poison dart frog is a tree frog that secretes poison when it gets attacked. Even a small amount of the toxin can be lethal to humans. Today, South American Indians use the poison to tip their arrowheads before hunting.

Many of the South American animals inspire the fascination which comes from revulsion.  Shoals of cannibal fish infest the rivers waiting to rip the flesh from any animal which tumbles among them, and vampire bats, a legend in Europe but a grim reality in South America, fly out at night from their roosts in the forests to suck blood from cows and men.