Pollination is the transfer of pollen from the male to the female part of a flower.

Because there is little air movement in the lower layers of the tropical rainforest, plants there tend to be pollinated by bats, birds and insects, rather than by the wind.

Pollinators usually visit flowers because they receive a reward in the form of pollen or nectar.

Nectar is a sugary solution secreted by glands in the flower. It often accumulates in special pouches or spurs so that it is inaccessible to all but a few insects.

In addition to sugars, some nectars contain amino acids, the building blocks of proteins.

Plants and their pollinators have usually adapted to one another.

Flowers pollinated by bats open at night. They are either large and strong enough to bear the weight and resist the bats' claws, or are grouped into dense masses that collectively function in the same way.

They have a disagreeable, musty smell, are white or a purplish shade and exude a great deal of sticky and gelatinous nectar.

Many flowers of the tropical rainforest have evolved to adapted attract bird pollinators. They open during the day, secrete copious amounts of nectar and are strongly constructed.

Flowers that are pollinated by birds are scentless. They are bright-colored often red and orange, because birds can see well into the red part of the spectrum.

Flowers pollinated by hummingbirds are red with protruding stamens and stigma. As a hummingbird hovers in front of a flower and inserts its long bill to reach the nectar, which is concealed either in a spur or at the base of a tube formed by the petals, both the stamens and stigma touch its head and body.

The flower-feeding birds of the Old World, such as the sunbirds and flower-peckers, often perch nearby on a bare stem, leaf stalk, bract or flower bud as they feed.

The flowers that are pollinated by insects are the most diverse.

Most of these are yellow or blue. A few that appear red to humans also reflect ultraviolet, which insects can detect. Insects are sensitive to the violet end of the spectrum and beyond.

The simplest insect-pollinated flowers are open-bowl-shaped. They often provide only pollen, and are visited by beetles.

Flowers with nectar in shallow spurs or wide tubes attract bees and flies, which have relatively short tongues.

Some bees will use their strong jaws to bite into narrow floral tubes, taking the nectar without pollinating the flower.

Butterflies and moths are the insects most highly adapted to flower feeding. Most have long, thin tongues that can reach to the bottom of the longest and narrowest spurs.

Some butterflies, especially the swallowtails, regularly visit red flowers and so may be able to see these wavelengths.

Nocturnal hawk moths, with long tongues and the ability to hover in front of a flower while feeding on it, are the insect equivalent of hummingbirds. They pollinate flowers that are sweet-scented, white, long-tubed and bloom at night.