page_title: Bird
section_title: Ecology
hierarchical_section_title: Bird / Ecology
caption_attribution_description: English: Male of the Gran Canaria blue chaffinch Español: Macho del pinzón azul de Gran Canaria
context_page_description: Birds are a group of warm-blooded vertebrates constituting the class Aves, characterized by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. There are about ten thousand living species, more than half of which are passerine, or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.
  Birds are a group of feathered theropod dinosaurs, and constitute the only living dinosaurs.
context_section_description: Birds occupy a wide range of ecological positions. While some birds are generalists, others are highly specialised in their habitat or food requirements. Even within a single habitat, such as a forest, the niches occupied by different species of birds vary, with some species feeding in the forest canopy, others beneath the canopy, and still others on the forest floor. Forest birds may be insectivores, frugivores, and nectarivores. Aquatic birds generally feed by fishing, plant eating, and piracy or kleptoparasitism. Birds of prey specialise in hunting mammals or other birds, while vultures are specialised scavengers. Avivores are animals that are specialised at preying on birds.
  Some nectar-feeding birds are important pollinators, and many frugivores play a key role in seed dispersal. Plants and pollinating birds often coevolve, and in some cases a flower's primary pollinator is the only species capable of reaching its nectar.
  Birds are often important to island ecology. Birds have frequently reached islands that mammals have not; on those islands, birds may fulfil ecological roles typically played by larger animals. For example, in New Zealand nine species of moa were important browsers, as are the kererū and kokako today. Today the plants of New Zealand retain the defensive adaptations evolved to protect them from the extinct moa. Nesting seabirds may also affect the ecology of islands and surrounding seas, principally through the concentration of large quantities of guano, which may enrich the local soil and the surrounding seas.
  A wide variety of avian ecology field methods, including counts, nest monitoring, and capturing and marking, are used for researching avian ecology.
caption: Gran Canaria blue chaffinch, an example of a bird highly specialised in its habitat, in this case in the Canarian pine forests.
exif: {"Image XResolution": "95", "Image YResolution": "95", "Image ResolutionUnit": "Pixels/Inch", "Image Copyright": "(C)M.A.Pena"}