Ornithophily or bird pollination is the pollination of flowering plants by birds. This sometimes (but not always) coevolutionary association is derived from insect pollination (entomophily) and is particularly well developed in some parts of the world, especially in the tropics, Southern Africa, and on some island chains. The association involves several distinctive plant adaptations forming a "pollination syndrome". The plants typically have colourful, often red, flowers with long tubular structures holding ample nectar and orientations of the stamen and stigma that ensure contact with the pollinator. Birds involved in ornithophily tend to be specialist nectarivores with brushy tongues and long bills, that are either capable of hovering flight or light enough to perch on the flower structures.

Plant adaptations for ornithophily can be grouped primarily into those that attract and facilitate pollen transfer by birds, and those that exclude other groups, primarily insects, protecting against 'theft' of nectar and pollen. The ovules of bird flowers also tend to have adaptations that protect them from damage during vigorous foraging by hard bird bills.

One of the general adaptation patterns is the red flower color for many plant species. The pollinator, birds, are tetrachromats, and one type of the single cone has specific opsin to detect long-wavelength light (below about 600 nm). Therefore, birds have red photoreceptors and are sensitive to red color, and red flower colors can have a strong contrast with green leaf background. Better bird attraction is thus the primary reason behind the red color adaptation. Moreover, flowers of generalist bird-pollinated species from the New World have purer red colors than those from the Old World, which often have a secondary reflectance peak around shorter-wavelength region. The secondary peak reduces the contrast of red color with the background and the avoidance of insects (higher risk of nectar robbing), decreasing the efficiency of pollination.

The flowers of generalist bird-pollinated plant species differ from those pollinated by specialized birds, such as hummingbirds or sunbirds by lacking long corolla tubes and having brush-like, exserted stamens. Most bird pollinated flowers are red and have a lot of nectar. They also tend to be unscented. Flowers with generalist pollinators tend to have dilute nectar but those that have specialist pollinators such as hummingbirds or sunbirds tend to have more concentrated nectar. The nectar of ornithophilous flowers vary in the sugar composition, with hexoses being high in passerine pollinated species while those that are insect pollinated tend to be sucrose rich. Hummingbird pollinated flowers however tend to be sucrose rich.

Different plants have also developed specific adaptations for bird pollination. Many plants of the family Loranthaceae have explosive flowers that shower pollen on a bird that forages near it. They are associated mainly with flowerpeckers in the family Dicaeidae. In Australia, some species of Banksia have flowers that open in response to bird actions thereby reducing the wastage of pollen. In tropical dry forests in southern India, ornithophilous flowers were found to bloom mainly in the hot dry season. Calceolaria uniflora, a species of Scrophularaceae from South America, has a special fleshy appendage on the lower lip of the flower that is rich in sugar. This is fed on by the least seedsnipe (Thinocorus rumicivorus) and in the process the birds brush pollen onto their head and transfer them to other flowers.

The rat's tail babiana (Babiana ringens) produces a strong stalk within the inflorescence that serves as a perch for the malachite sunbird as it visits the flower. Heliconias have special sticky threads that help in the adhesion of pollen to smooth structures such as the bill of a hummingbird. Some African orchids of the genus Disa have pollinaria that stick to the feet of visiting sunbirds.

Plants need to protect against nectar and pollen being taken by non-pollinators. Such animals are sometimes classified as thieves, which simply remove resources without pollinating, and robbers, which damage the flower to access resources. Flowers specialized for pollination by long-billed birds may be especially vulnerable to theft. For example, some bees and birds that cannot reach down the long tubes of bird pollinated flowers simply pierce the flower at the base to obtain nectar, without pollinating.

The main families of specialized nectar feeding birds that are involved in ornithophily are the hummingbirds (Trochilidae), sunbirds (Nectariniidae), and the honey-eaters (Meliphagidae). Other important bird groups include those in the families the Icteridae, the honeycreepers (Thraupidae, Carduelinae), white-eyes (Zosteropidae) and the South African sugar-birds (Promeropidae). Birds may obtain nectar either by perching or by hovering with the latter mainly found in the hummingbirds and sunbirds. Within the hummingbirds, two kinds of foraging are noted with non-territorial "hermit" hummingbirds which forage longer distances and the territorial non-hermits.