Ornithophily
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 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.
The pollinator, birds, are tetrachromats, and one type of the single cone has specific opsin to detect long-wavelength light (below about 600 nm).
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.
[8][9] 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.
[17] 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.
[24] 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).
[26] Hummingbirds are capable of excreting nitrogenous wastes as ammonia since they can afford more water loss than birds that feed on low-moisture food sources.
[33] Tropical China and the adjacent Indochinese countries harbor relatively few bird-pollinated flowers, among them is Rhodoleia championii, a member of the family Hamamelidaceae, which at any one site can be visited and pollinated by up to seven species of nectar-foraging birds, including Japanese white-eyes (Zosterops japonicus, Zosteropidae) and fork-tailed sunbirds (Aethopyga christinae, Nectariniidae).
This creates a favorable upright body position for hummingbirds during feeding, one that allows them to sufficiently flap their wings for hovering.
[42] High altitude ecosystems that lack insect pollinators, those in dry regions or isolated islands tend to favour the evolution of ornithophily, most by specialized nectarivorous birds, such as hummingbirds or sunbirds.
[5] Plants pollinated by generalist birds are most diverse in tropical and subtropical lowlands with a pronounced climatic seasonality.
[43] Generalist bird-pollinated plants even evolved deterring mechanisms against specialized nectarivorous birds and bees since these groups tend to establish feeding territories within one tree and thus most conduct self-pollination.
