Abstract: The life of birds is based on flight, which has both constrained their diversification and opened ecological opportunities. It affects their size and their abundance. Their ecology is based on the exploitation of patchy and variable resources, migration being the most obvious manifestation of this. A few birds are flightless. The taxonomic diversity of birds is limited. Across all continents, bird species diversity is greater in wooded than in forested habitats, generally being related to habitat complexity and productivity. Coexisting species eat different foods and often use different parts of the habitat. Bird species diversity is greater where there is greater habitat diversity; it is less at higher altitudes; and it is generally less as one moves from the tropics toward the poles, with strong local modifications. It may be correlated with that of other animals, but not always. Bird data have been used to test hypotheses about the causes of the latitudinal gradient in biodiversity. There is evidence that it is partly dependent on tropical regions providing more ecological opportunities, more habitable area, and more utilizable energy. No species is found all over the world. Some closely related species replace each other geographically. Some parts of the world, mainly tropical, have unusually large numbers of endemic, restricted-range species. Geological and evolutionary history has resulted in the avifaunas of different regions of the world differing in richness and taxonomic origin. Unrelated species living in different places but similar habitats have often undergone evolutionary convergence. Birds are good colonists of islands, where they subsequently evolve in the presence of few (if any) other land vertebrates. More species are found on larger islands, on those that once formed parts of larger landmasses, and on those closer to sources of colonists. Islands that become cut off from the mainland or which are fragmented lose species because extinctions are not then sufficiently matched by colonizations. Humans have caused the extinction of many birds, in both historical and prehistorical times, especially on islands. The chief current threats to them are habitat loss, hunting, agricultural intensification, and the introduction of alien species to islands. Reducing these threats will be difficult. Avian biodiversity continues to be lost both by large-scale declines of many species in some parts of the world and by the introduction of species without their native ranges, which diminishes the differences in the bird communities of different lands.
Publication Year: 2001
Publication Date: 2001-01-01
Language: en
Type: book-chapter
Indexed In: ['crossref']
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Cited By Count: 2
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