Taxobox
name = Birds
fossil_range = Fossil range|150|0Late Jurassic – Recent
image_width = 240px
image_caption = Double-crested Cormorant, "Phalacrocorax auritus"
regnum = Animalia
phylum = Chordata
subphylum = Vertebrata
unranked_classis = Archosauria
classis = Aves
classis_authority = Linnaeus, 1758
subdivision_ranks = Orders
subdivision =About two dozen - see section below
Birds (class Aves) are bipedal, endothermic (warm-blooded), vertebrate animals that lay eggs. There are around 10,000 living species, making them the most diverse tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the convert|5|cm|in|sigfig=1|abbr=on Bee Hummingbird to the convert|2.7|m|sigfig=1|abbr=on Ostrich. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, around 150–200 Ma (million years ago), and the earliest known bird is the Late Jurassic "Archaeopteryx", "c" 155–150 Ma. Most paleontologists regard birds as the only clade of dinosaurs that survived the Cretaceous–Tertiary extinction event approximately 65.5 Ma.
Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All birds have forelimbs modified as wings and most can fly, with some exceptions including ratites, penguins, and a number of diverse endemic island species. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.
Many species undertake long distance annual migrations, and many more perform shorter irregular movements. Birds are social; they communicate using visual signals and through calls and songs, and participate in social behaviours including cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous ("many females") or, rarely, polyandrous ("many males"). Eggs are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
Many species are of economic importance, mostly as sources of food acquired through hunting or farming. Some species, particularly songbirds and parrots, are popular as pets. Other uses include the harvesting of guano (droppings) for use as a fertiliser. Birds figure prominently in all aspects of human culture from religion to poetry to popular music. About 120–130 species have become extinct as a result of human activity since the 17th century, and hundreds more before then. Currently about 1,200 species of birds are threatened with extinction by human activities, though efforts are underway to protect them.
Evolution and taxonomy
The first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume "Ornithologiae". [cite book |last=del Hoyo |first=Josep |coauthors=Andy Elliott & Jordi Sargatal |title=Handbook of Birds of the World, Volume 1: Ostrich to Ducks |year=1992 |publisher=Lynx Edicions |location=Barcelona |isbn=84-87334-10-5]
Carolus Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use. [la icon cite book |last=Linnaeus |first=Carolus |authorlink=Carolus Linnaeus |title=Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata |publisher=Holmiae. (Laurentii Salvii) |year=1758 |pages=824 |url=] Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda.[cite journal |last=Livezey |first=Bradley C. |coauthors=Richard L. Zusi |month=January |year=2007 |title=Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion |journal=Zoological Journal of the Linnean Society |volume=149 |issue=1 |pages=1–95 |doi=10.1111/j.1096-3642.2006.00293.x] Aves and a sister group, the clade Crocodilia, together are the sole living members of the reptile clade Archosauria. Phylogenetically, Aves is commonly defined as all descendants of the most recent common ancestor of modern birds and "Archaeopteryx lithographica". [] "Archaeopteryx", from the Kimmeridgian stage of the Late Jurassic (some 155–150 million years ago), is the earliest known bird under this definition. Others, including Jacques Gauthier and adherents of the Phylocode system, have defined Aves to include only the modern bird groups, excluding most groups known only from fossils, and assigning them, instead, to the Avialae [cite book |last=Gauthier |first=Jacques|editor=Kevin Padian |title=The Origin of Birds and the Evolution of Flight|Series= Memoirs of the California Academy of Science 8|year=1986|pages=1–55|chapter=Saurischian Monophyly and the origin of birds|isbn=0-940228-14-9] in part to avoid the uncertainties about the placement of "Archaeopteryx" in relation to animals traditionally thought of as theropod dinosaurs. ]All modern birds lie within the subclass Neornithes, which has two subdivisions: the Paleognathae, containing mostly flightless birds like ostriches, and the wildly diverse Neognathae, containing all other birds.
Dinosaurs and the origin of birds
Fossil evidence and intensive biological analyses have demonstrated beyond any reasonable doubt that birds are theropod
dinosaurs. More specifically, they are members of Maniraptora, a group of theropods which includes dromaeosaurs and oviraptorids, among others. [cite book |last=Paul |first=Gregory S. |authorlink=Gregory S. Paul |chapter=Looking for the True Bird Ancestor |year=2002 |title=Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds |location=Baltimore
publisher=John Hopkins University Press |isbn=0-8018-6763-0
pages=171–224] As scientists discover more non-avian theropods that are closely related to birds, the previously clear distinction between non-birds and birds has become blurred. Recent discoveries in the Liaoning Province of northeast China, which demonstrate that many small theropod dinosaurs had feathers, contribute to this ambiguity. [cite book |last=Norell |first=Mark |coauthors=Mick Ellison |year=2005 |title=Unearthing the Dragon: The Great Feathered Dinosaur Discovery |location=New York
publisher=Pi Press |isbn=0-13-186266-9|pages=]
The consensus view in contemporary paleontology is that the birds, Aves, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and troodontids. Together, these three form a group called Paraves. The basal dromaeosaur "Microraptor" has features which may have enabled it to glide or fly. The most basal deinonychosaurs are very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal, and/or may have been able to glide.[cite journal |last=Turner |first=Alan H. |coauthors=Pol, Diego; Clarke, Julia A.; Erickson, Gregory M.; and Norell, Mark |year=2007 |title=A basal dromaeosaurid and size evolution preceding avian flight |url=http://www.sciencemag.org/cgi/reprint/317/5843/1378.pdf |format=pdf |journal=Science|volume=317 |pages=1378–1381 |doi=10.1126/science.1144066 |pmid=17823350 ] ][cite journal|author=Xing, X., Zhou, Z., Wang, X., Kuang, X., Zhang, F., and Du, X.|year=2003|title=Four-winged dinosaurs from China|journal=Nature|volume=421|issue=6921|pages=335–340|doi=10.1038/nature01342] ]The Late Jurassic "Archaeopteryx" is well-known as one of the first transitional fossils to be found and it provided support for the theory of evolution in the late 19th century. "Archaeopteryx" has clearly reptilian characters: teeth, clawed fingers, and a long, lizard-like tail, but it has finely preserved wings with flight feathers identical to those of modern birds. It is not considered a direct ancestor of modern birds, but is the oldest and most primitive member of Aves or Avialae, and it is probably closely related to the real ancestor. It has even been suggested that "Archaeopteryx" was a dinosaur that was no more closely related to birds than were other dinosaur groups,[cite journal|author=Thulborn, R.A.|year=1984|title=The avian relationships of "Archaeopteryx", and the origin of birds|journal=Zoological Journal of the Linnean Society|volume=82|pages=119–158|doi=10.1111/j.1096-3642.1984.tb00539.x] and that "Avimimus" was more likely to be the ancestor of all birds than "Archaeopteryx".][cite journal|author=Kurzanov, S.M.|year=1987|title=Avimimidae and the problem of the origin of birds|journal=Transactions of the joint Soviet - Mongolian Paleontological Expedition|volume=31|pages=31–94] ]Alternative theories and controversies
There have been many controversies in the study of the origin of birds. Early disagreements included whether birds evolved from dinosaurs or more primitive archosaurs. Within the dinosaur camp there were disagreements as to whether ornithischian or theropod dinosaurs were the more likely ancestors.[Heilmann, Gerhard. "The origin of birds" (1927) "Dover Publications", New York.] Although ornithischian (bird-hipped) dinosaurs share the hip structure of modern birds, birds are thought to have originated from the saurischian (lizard-hipped) dinosaurs, and therefore evolved their hip structure independently. [cite journal |last=Rasskin-Gutman |first=Diego |coauthors=Angela D. Buscalioni |month=March |year=2001 |title=Theoretical morphology of the Archosaur (Reptilia: Diapsida) pelvic girdle |journal=Paleobiology |volume=27 |issue=1 |pages=59–78|doi=10.1666/0094-8373(2001) |doi_brokendate=2008-06-28] In fact, a bird-like hip structure evolved a third time among a peculiar group of theropods known as the Therizinosauridae.]Scientists Larry Martin and Alan Feduccia believe that birds are not dinosaurs, but that birds evolved from early archosaurs like "Longisquama". The majority of their publications argued that the similarities between birds and maniraptoran dinosaurs were convergent, and that the two were unrelated. In the late 1990s the evidence that birds were maniraptorans became almost indisputable, so Martin and Feduccia adopted a modified version of a hypothesis by dinosaur artist Gregory S. Paul; where maniraptorans are secondarily flightless birds but, [cite book |author=Paul, Gregory S. |title=Dinosaurs of the air: the evolution and loss of flight in dinosaurs and birds |publisher=Johns Hopkins University Press |location=Baltimore |year=2002 |pages=224-258 |isbn=0-8018-6763-0 |oclc= |doi=] in their version, birds evolved directly from Longisquama. Thus birds are still not dinosaurs, but neither are most of the known species that are currently classified as theropod dinosaurs. Maniraptorans are, instead, flightless, archosaurian, birds. [cite journal |last=Feduccia |first=Alan |coauthors=Theagarten Lingham-Soliar, J. Richard Hinchliffe |month=November |year=2005|title=Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence
journal=Journal of Morphology |volume=266 |issue=2 |pages=125–66
doi=10.1002/jmor.10382 |pmid=16217748] This theory is contested by most paleontologists. [cite journal |last=Prum |first=Richard O. |month=April |year=2003 |title=Are Current Critiques Of The Theropod Origin Of Birds Science? Rebuttal To Feduccia 2002
journal=The Auk |volume=120 |issue=2 |pages=550–61
url=http://links.jstor.org/sici?sici=0004-8038(200304)120:2%3C550:ACCOTT%3E2.0.CO;2-0 |doi=10.1642/0004-8038(2003)120 [0550:ACCOTT] 2.0.CO;2] The features cited as evidence of flightlessness are interpreted by mainstream paleontologists as exaptations, or "pre-adaptations", that maniraptorans inherited from their common ancestor with birds.
"Protoavis texensis" was described in 1991 as a bird older than Archaeopteryx. Critics have indicated that the fossil is poorly preserved, extensively reconstructed, and may be a chimera (made up of fossilized bones from several different kinds of animals). The braincase is most likely that of a very early coelurosaur [cite journal |last=Zhou |first=Zhonghe |month=October |year=2004 |title=The origin and early evolution of birds: discoveries, disputes, and perspectives from fossil evidence
journal=Die Naturwissenschaften |volume=91 |issue=10 |pages=455–71 |doi=10.1007/s00114-004-0570-4]
Early evolution of birds
clade|style=font-size:75%
label1=Aves
1=clade
1="Archaeopteryx"
label2= Pygostylia
2=clade
1=Confuciusornithidae
label2= Ornithothoraces
2=clade
1=Enantiornithes
label2= Ornithurae
2=clade
1=Hesperornithiformes
2=Neornithes
Basal bird phylogeny simplified after Chiappe, 2007[cite book |last=Chiappe |first=Luis M. |year=2007 |title=Glorified Dinosaurs: The Origin and Early Evolution of Birds |location=Sydney |publisher=University of New South Wales Press |isbn=978-0-86840-413-4] ]
Birds diversified into a wide variety of forms during the Cretaceous Period.
The first large, diverse lineage of short-tailed birds to evolve were the Enantiornithes, or "opposite birds", so named because the construction of their shoulder bones was in reverse to that of modern birds. Enantiornithes occupied a wide array of ecological niches, from sand-probing shorebirds and fish-eaters to tree-dwelling forms and seed-eaters.
Radiation of modern birds
Containing all modern birds, the subclass Neornithes is, due to the discovery of "Vegavis", now known to have evolved into some basic lineages by the end of the Cretaceous [cite journal |last=Clarke |first=Julia A. |coauthors=Claudia P. Tambussi, Jorge I. Noriega, Gregory M. Erickson and Richard A. Ketcham |month=January |year=2005 |title=Definitive fossil evidence for the extant avian radiation in the Cretaceous |journal=Nature |volume=433 |issue= |pages=305–308 |doi=10.1038/nature03150 |pmid=15662422 |url=http://www.digimorph.org/specimens/Vegavis_iaai/nature03150.pdf [http://www.nature.com/nature/journal/v433/n7023/suppinfo/nature03150.html Supporting information] ] and is split into two superorders, the Paleognathae and Neognathae. The paleognaths include the tinamous of Central and South America and the ratites. The basal divergence from the remaining Neognathes was that of the Galloanserae, the superorder containing the Anseriformes (ducks, geese, swans and screamers) and the Galliformes (the pheasants, grouse, and their allies, together with the mound builders and the guans and their allies). The dates for the splits are much debated by scientists. It is agreed that the Neornithes evolved in the Cretaceous, and that the split between the Galloanseri from other Neognathes occurred before the K–T extinction event, but there are different opinions about whether the radiation of the remaining Neognathes occurred before or after the extinction of the other dinosaurs.[cite journal |last=Ericson |first=Per G.P. |coauthors=Cajsa L. Anderson, Tom Britton "et al." |month=December |year=2006 |title=Diversification of Neoaves: Integration of molecular sequence data and fossils |journal=Biology Letters |volume=2 |issue=4 |pages=543–547 |doi=10.1098/rsbl.2006.0523 |pmid=17148284 |url=http://www.senckenberg.de/files/content/forschung/abteilung/terrzool/ornithologie/neoaves.pdf] This disagreement is in part caused by a divergence in the evidence; molecular dating suggests a Cretaceous radiation, while fossil evidence supports a Tertiary radiation. Attempts to reconcile the molecular and fossil evidence have proved controversial.]The classification of birds is a contentious issue. Sibley and Ahlquist's "Phylogeny and Classification of Birds" (1990) is a landmark work on the classification of birds, [cite book |last=Sibley |first=Charles |coauthors=Jon Edward Ahlquist |year=1990 |title=Phylogeny and classification of birds |location=New Haven |publisher=Yale University Press |isbn=0-300-04085-7|pages=] although it is frequently debated and constantly revised. Most evidence seems to suggest that the assignment of orders is accurate, [cite book |last=Mayr |first=Ernst |coauthors=Short, Lester L.|title=Species Taxa of North American Birds/A Contribution to Comparative Systematics|year=1970 |publisher=Nuttal Orinthological Club|location=Cambridge |oclc=517185] but scientists disagree about the relationships between the orders themselves; evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem, but no strong consensus has emerged. More recently, new fossil and molecular evidence is providing an increasingly clear picture of the evolution of modern bird orders.
Modern bird orders
clade
label1=Neornithes
1=clade
label1=Paleognathae
1=clade
1=Struthioniformes
2=Tinamiformes
label2= Neognathae
2=clade
1=Other birds
label1=
label2=Galloanserae
2=clade
1=Anseriformes
2=Galliformes
Basal divergences of modern birds based on Sibley-Ahlquist taxonomy
This is a list of the taxonomic orders in the subclass Neornithes, or modern birds. This list uses the traditional classification (the so-called Clements order), revised by the Sibley-Monroe classification. The list of birds gives a more detailed summary of the orders, including families.
Subclass Neornithes
Paleognathae:
* Struthioniformes—ostriches, emus, kiwis, and allies
* Tinamiformes—tinamous
Neognathae:
* Anseriformes—waterfowl
* Galliformes—fowl
* Charadriiformes—gulls, button-quails, plovers and allies
* Gaviiformes—loons
* Podicipediformes—grebes
* Procellariiformes—albatrosses, petrels, and allies
* Sphenisciformes—penguins
* Pelecaniformes—pelicans and allies
* Phaethontiformes—tropicbirds
* Ciconiiformes—storks and allies
* Cathartiformes—New World vultures
* Phoenicopteriformes—flamingos
* Falconiformes—falcons, eagles, hawks and allies
* Gruiformes—cranes and allies
* Pteroclidiformes—sandgrouse
* Columbiformes—doves and pigeons
* Psittaciformes—parrots and allies
* Cuculiformes—cuckoos and turacos
* Opisthocomiformes—hoatzin
* Strigiformes—owls
* Caprimulgiformes—nightjars and allies
* Apodiformes—swifts and hummingbirds
* Coraciiformes—kingfishers and allies
* Piciformes—woodpeckers and allies
* Trogoniformes—trogons
* Coliiformes—mousebirds
* Passeriformes—passerines
The radically different Sibley-Monroe classification (Sibley-Ahlquist taxonomy), based on molecular data, found widespread adoption in a few aspects, as recent molecular, fossil, and anatomical evidence supported the Galloanserae for example.
Distribution
Birds live and breed in most terrestrial habitats and on all seven continents, reaching their southern extreme in the Snow Petrel's breeding colonies up to convert|440|km|mi|-1 inland in Antarctica. [cite book |last=Brooke |first=Michael |year=2004 |title=Albatrosses And Petrels Across The World |location=Oxford |publisher=Oxford University Press|isbn=0-19-850125-0|pages=] The highest bird diversity occurs in tropical regions. It was earlier thought that this high diversity was the result of higher speciation rates in the tropics, however recent studies found higher speciation rates in the high latitudes that were offset by greater extinction rates than in the tropics. [cite journal |last=Weir |first=Jason T. |coauthors=Dolph Schluter |month=March |year=2007 |title=The Latitudinal Gradient in Recent Speciation and Extinction Rates of Birds and Mammals |journal=Science |volume=315 |issue=5818 |pages=1574–76 |doi=10.1126/science.1135590 |pmid=17363673] Several families of birds have adapted to life both on the world's oceans and in them, with some seabird species coming ashore only to breed[cite book |last=Schreiber |first=Elizabeth Anne |coauthors=Joanna Burger |year=2001 |title=Biology of Marine Birds |location=Boca Raton |publisher=CRC Press |isbn=0-8493-9882-7|pages=] and some penguins have been recorded diving up to convert|300|m|ft|-1. [cite journal |last=Sato |first=Katsufumi |coauthors=Y. Naito, A. Kato "et al." |month=May |year=2002 |title=Buoyancy and maximal diving depth in penguins: do they control inhaling air volume? |journal=Journal of Experimental Biology |volume=205 |issue=9 |pages=1189–1197 |pmid=11948196 |url=http://jeb.biologists.org/cgi/content/full/205/9/1189] ]Many bird species have established breeding populations in areas to which they have been introduced by humans. Some of these introductions have been deliberate; the Ring-necked Pheasant, for example, has been introduced around the world as a game bird. [cite book |last=Hill |first=David |coauthors=Peter Robertson |year=1988 |title=The pheasant: Ecology, Management, and Conservation |location=Oxford |publisher=BSP Professional |isbn=0-632-02011-3|pages=] Others have been accidental, such as the establishment of wild Monk Parakeets in several North American cities after their escape from captivity. [cite web|last=Spreyer |first=Mark F.|coauthors=Enrique H. Bucher|year=1998|title=Monk Parakeet (Myiopsitta monachus)|work=The Birds of North America|publisher=Cornell Lab of Ornithology|url=http://bna.birds.cornell.edu/bna/species/322 |doi=10.2173/bna.322] Some species, including Cattle Egret, [cite journal |last=Arendt |first=Wayne J. |year=1988 |title=Range Expansion of the Cattle Egret, ("Bubulcus ibis") in the Greater Caribbean Basin |journal=Colonial Waterbirds |volume=11 |issue=2 |pages=252–62 |doi=10.2307/1521007] Yellow-headed Caracara [cite book |last=Bierregaard |first=R.O. |year=1994 |chapter=Yellow-headed Caracara |editor=Josep del Hoyo, Andrew Elliott & Jordi Sargatal (eds.) |title=Handbook of the Birds of the World. Volume 2; New World Vultures to Guineafowl |location=Barcelona |publisher=Lynx Edicions |isbn=84-87334-15-6|pages=] and Galah, [cite book |last=Juniper |first=Tony |coauthors=Mike Parr |year=1998 |title=Parrots: A Guide to the Parrots of the World |location=London |publisher=Christopher Helm |isbn=0-7136-6933-0|pages=] have spread naturally far beyond their original ranges as agricultural practices created suitable new habitat.
Anatomy and physiology
Compared with other vertebrates, birds have a body plan that shows many unusual adaptations, mostly to facilitate flight.
The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the respiratory system. [cite web |last=Ehrlich |first=Paul R. |coauthors=David S. Dobkin, and Darryl Wheye |title=Adaptations for Flight |url=http://www.stanford.edu/group/stanfordbirds/text/essays/Adaptations.html |year=1988 |work=Birds of Stanford |publisher=Stanford University |accessdate=2007-12-13 Based on The Birder's Handbook (Paul Ehrlich, David Dobkin, and Darryl Wheye. 1988. Simon and Schuster, New York.)] The skull bones are fused and do not show cranial sutures.[cite book |last=Gill |first=Frank |year=1995 |title=Ornithology |publisher=WH Freeman and Co |location=New York |isbn=0-7167-2415-4 |pages=] The orbits are large and separated by a bony septum. The spine has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior thoracic vertebrae and absent in the later vertebrae. [cite news |title=The Avian Skeleton |url=http://www.paulnoll.com/Oregon/Birds/Avian-Skeleton.html |work=paulnoll.com |accessdate=2007-12-13] The last few are fused with the pelvis to form the synsacrum.]Like the reptiles, birds are primarily uricotelic, that is, their kidneys extract nitrogenous wastes from their bloodstream and excrete it as uric acid instead of urea or ammonia via the ureters into the intestine. Birds do not have a urinary bladder or external urethral opening and uric acid is excreted along with feces as a semisolid waste. [cite web |last=Ehrlich |first=Paul R. |coauthors=David S. Dobkin, and Darryl Wheye |title=Drinking |url=http://www.stanford.edu/group/stanfordbirds/text/essays/Drinking.html |year=1988 |work=Birds of Stanford |publisher=Standford University |accessdate=2007-12-13] [cite journal |last=Tsahar |first=Ella|coauthors=Carlos Martínez del Rio, Ido Izhaki and Zeev Arad |title=Can birds be ammonotelic? Nitrogen balance and excretion in two frugivores |journal=Journal of Experimental Biology |volume=208 |issue=6 |pages=1025–34 |year=2005 |pmid=15767304 |doi=10.1242/jeb.01495 ] However, birds such as hummingbirds can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia. [cite journal |last=Preest |first=Marion R. |coauthors=Carol A. Beuchat |month=April |year=1997 |title=Ammonia excretion by hummingbirds |journal=Nature |volume=386 |issue= |pages=561–62 |doi=10.1038/386561a0] They also excrete creatine, rather than creatinine like mammals.[cite book |last=Attenborough |first=David |authorlink=David Attenborough |year=1998 |title=The Life of Birds |location=Princeton |publisher=Princeton University Press |isbn=0-691-01633-X|pages=] Some migratory birds have adapted to use protein from many parts of their bodies, including protein from the intestines, as additional energy during migration.][cite journal |last=Battley |first=Phil F. |coauthors=Theunis Piersma, Maurine W. Dietz "et als." |month=January |year=2000 |title=Empirical evidence for differential organ reductions during trans-oceanic bird flight |journal=Proceedings of the Royal Society B |volume=267 |issue=1439 |pages=191–5 |doi=10.1098/rspb.2000.0986 |pmid=10687826 (Erratum in "Proceedings of the Royal Society B" 267(1461):2567.)] ]Birds have one of the most complex respiratory systems of all animal groups.[cite book |last=Suthers |first=Roderick A. |coauthors=Sue Anne Zollinger |chapter=Producing song: the vocal apparatus |editor=H. Philip Zeigler & Peter Marler (eds.) |year=2004 |title=Behavioral Neurobiology of Birdsong |series=Annals of the New York Academy of Sciences 1016 |location=New York |publisher=New York Academy of Sciences |isbn=1-57331-473-0 |pages=109-129 |doi=10.1196/annals.1298.041 PMID 15313772] The bird's heart has four chambers and the right aortic arch gives rise to systemic circulation (unlike in the mammals where the left arch is involved).]The nervous system is large relative to the bird's size.[cite web |last=Ehrlich |first=Paul R. |coauthors=David S. Dobkin, and Darryl Wheye |title=The Avian Sense of Smell |url=http://www.stanford.edu/group/stanfordbirds/text/essays/Avian_Sense.html |year=1988 |work=Birds of Stanford |publisher=Standford University |accessdate=2007-12-13] and tubenoses. [cite journal |last=Lequette |first=Benoit |coauthors=Christophe Verheyden, Pierre Jouventin |month=August |year=1989 |title=Olfaction in Subantarctic seabirds: Its phylogenetic and ecological significance |journal=The Condor |volume=91 |issue=3 |pages=732–35 |doi=10.2307/1368131 |url=http://elibrary.unm.edu/sora/Condor/files/issues/v091n03/p0732-p0735.pdf] The avian visual system is usually highly developed. Water birds have special flexible lenses, allowing accommodation for vision in air and water.]A few species are able to use chemical defenses against predators; some Procellariiformes can eject an unpleasant oil against an aggressor, [cite journal |last=Warham |first=John |year=1977 |title=The Incidence, Function and ecological significance of petrel stomach oils |journal=Proceedings of the New Zealand Ecological Society |volume=24 |pages=84–93 |url=http://www.newzealandecology.org/nzje/free_issues/ProNZES24_84.pdf |doi=10.2307/1365556|format=PDF] and some species of pitohuis from New Guinea secrete a powerful neurotoxin in their skin and feathers. [cite journal |last=Dumbacher |first=J.P. |coauthors=B.M. Beehler, T.F. Spande "et als." |month=October |year=1992 |title=omobatrachotoxin in the genus "Pitohui": chemical defense in birds? |journal=Science |volume=258 |issue=5083 |pages=799–801 |doi=10.1126/science.1439786 |pmid=1439786]
Chromosomes
Birds have two sexes: male and female. Birds' sex is determined by Z and W sex chromosomes, rather than the X and Y chromosomes seen in mammals. Males carry two Z chromosomes (ZZ), and females carry a W chromosome and a Z chromosome (WZ).
Feathers, plumage, and scales
Feathers are a feature unique to birds. They facilitate flight, provide insulation that aids in thermoregulation, and are used in display, camouflage, and signaling.
Plumage is regularly moulted; the standard plumage of a bird that has moulted after breeding is known as the "non-breeding" plumage, or – in the Humphrey-Parkes terminology – "basic" plumage; breeding plumages or variations of the basic plumage are known under the Humphrey-Parkes system as "alternate" plumages. [cite journal |last=Humphrey |first=Philip S. |coauthors=Kenneth C. Parkes |year=1959 |title=An approach to the study of molts and plumages |journal=The Auk |volume=76 |pages=1–31 |url=http://elibrary.unm.edu/sora/Auk/v076n01/p0001-p0031.pdf |doi=10.2307/3677029|format=PDF] Moulting is annual in most species, although some may have two moults a year, and large birds of prey may moult only once every few years. Moulting patterns vary across species. In passerines, flight feathers are replaced one at a time with the innermost primary being the first. When the fifth of sixth primary is replaced, the outermost tertiaries begin to drop. After the innermost tertiaries are moulted, the secondaries starting from the innermost begin to drop and this proceeds to the outer feathers (centrifugal moult). The greater primary coverts are moulted in synchrony with the primary that they overlap.[cite book|author=Pettingill Jr. OS|year=1970|title=Ornithology in Laboratory and Field.|isbn=808716093|publisher=Burgess Publishing Co.] A small number of species, such as ducks and geese, lose all of their flight feathers at once, temporarily becoming flightless.][de Beer SJ, Lockwood GM, Raijmakers JHFS, Raijmakers JMH, Scott WA, Oschadleus HD, Underhill LG (2001). [http://web.uct.ac.za/depts/stats/adu/ringmanual.htm SAFRING Bird Ringing Manual.] SAFRING.] As a general rule, the tail feathers are moulted and replaced starting with the innermost pair.][ Centripetal moults of tail feathers are however seen in the Phasianidae. [cite journal |last=Gargallo|first=Gabriel|year=1994|month= |title=Flight Feather Moult in the Red-Necked Nightjar "Caprimulgus ruficollis" |journal=Journal of Avian Biology |volume=25|issue=2|pages=119–24 |doi=10.2307/3677029] The centrifugal moult is modified in the tail feathers of woodpeckers and treecreepers, in that it begins with the second innermost pair of feathers and finishes with the central pair of feathers so that the bird maintains a functional climbing tail.][ [cite journal |last=Mayr |first=Ernst |coauthors=Margaret Mayr |year=1954|title=The tail molt of small owls |journal=The Auk |volume=71 |issue=2 |pages=172–78 |url=http://elibrary.unm.edu/sora/Auk/v071n02/p0172-p0178.pdf|doi=10.1086/515854|doi_brokendate=2008-06-28|format=PDF] The general pattern seen in passerines is that the primaries are replaced outward, secondaries inward, and the tail from center outward. [cite web|first=Robert B.|last=Payne|title=Birds of the World, Biology 532|url=http://www.ummz.umich.edu/birds/resources/families_otw.html|publiher=Bird Division, University of Michigan Museum of Zoology|accessdate=2007-10-20] Before nesting, the females of most bird species gain a bare brood patch by losing feathers close to the belly. The skin there is well supplied with blood vessels and helps the bird in incubation. [cite journal |last=Turner |first=J. Scott |year=1997 |title=On the thermal capacity of a bird's egg warmed by a brood patch |journal=Physiological Zoology |volume=70 |issue=4 |pages=470–80 |doi=10.1086/515854 |pmid=9237308 |doi_brokendate=2008-06-28] Feathers require maintenance and birds preen or groom them daily, spending an average of around 9% of their daily time on this. [cite journal |last=Walther |first=Bruno A. |coauthors=Dale H. Clayton |year=2005 |title=Elaborate ornaments are costly to maintain: evidence for high maintenance handicaps |journal=Behavioural Ecology |volume=16 |issue=1 |pages=89–95 |doi=10.1093/beheco/arh135] The bill is used to brush away foreign particles and to apply waxy secretions from the uropygial gland; these secretions protect the feathers' flexibility and act as an antimicrobial agent, inhibiting the growth of feather-degrading bacteria. [cite journal |last=Shawkey |first=Matthew D. |coauthors=Shawkey, Shreekumar R. Pillai, Geoffrey E. Hill |year=2003 |title=Chemical warfare? Effects of uropygial oil on feather-degrading bacteria |journal=Journal of Avian Biology |volume=34 |issue=4 |pages=345–49 |doi=10.1111/j.0908-8857.2003.03193.x] This may be supplemented with the secretions of formic acid from ants, which birds receive through a behaviour known as anting, to remove feather parasites. [cite journal |last=Ehrlich |first=Paul R. |coauthors=David S. Dobkin, Darryl Wheye |year=1986 |title=The Adaptive Significance of Anting |journal=The Auk |volume=103 |issue=4 |pages=835 |url=http://elibrary.unm.edu/sora/Auk/v103n04/p0835-p0835.pdf] ]The scales of birds are composed of the same keratin as beaks, claws, and spurs. They are found mainly on the toes and metatarsus, but may be found further up on the ankle in some birds. Most bird scales do not overlap significantly, except in the cases of kingfishers and woodpeckers.The scales of birds are thought to be homologous to those of reptiles and mammals [cite book |last=Lucas |first=Alfred M. |year=1972 |title=Avian Anatomy - integument |location=East Lansing, Michigan, USA |publisher=USDA Avian Anatomy Project, Michigan State University |pages=67, 344, 394-601] .
Flight
Most birds can fly, which distinguishes them from almost all other vertebrates. Flight is the primary means of locomotion for most bird species and is used for breeding, feeding, and predator avoidance and escape. Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles (the pectoralis—accounting for 15% of the total mass of the bird—and the supracoracoideus), and a modified forelimb (wing) that serves as an aerofoil.
<109::AID-JMOR2>3.0.CO;2-0 |doi_brokendate=2008-06-28]
Behaviour
Most birds are diurnal, but some birds, such as many species of owls and nightjars, are nocturnal or crepuscular (active during twilight hours), and many coastal waders feed when the tides are appropriate, by day or night. [cite journal |last=Robert |first=Michel |coauthors=Raymond McNeil, Alain Leduc |month=January |year=1989 |title=Conditions and significance of night feeding in shorebirds and other water birds in a tropical lagoon |journal=The Auk |volume=106 |issue=1 |pages=94–101 |url=http://elibrary.unm.edu/sora/Auk/v106n01/p0094-p0101.pdf]
Diet and feeding
Birds' diets are varied and often include nectar, fruit, plants, seeds, carrion, and various small animals, including other birds.
Birds that employ many strategies to obtain food or feed on a variety of food items are called generalists, while others that concentrate time and effort on specific food items or have a single strategy to obtain food are considered specialists.
doi_brokendate=2008-06-28]
Migration
Many bird species migrate to take advantage of global differences of seasonal temperatures, therefore optimising availability of food sources and breeding habitat. These migrations vary among the different groups. Many landbirds, shorebirds, and waterbirds undertake annual long distance migrations, usually triggered by the length of daylight as well as weather conditions. These birds are characterised by a breeding season spent in the temperate or arctic/antarctic regions and a non-breeding season in the tropical regions or opposite hemisphere. Before migration, birds substantially increase body fats and reserves and reduce the size of some of their organs.[cite journal |last=Klaassen |first=Marc |coauthors= |month= |year=1996 |title=Metabolic constraints on long-distance migration in birds |journal=Journal of Experimental Biology |volume=199 |issue=1 |pages=57–64 |pmid=9317335 |url=http://jeb.biologists.org/cgi/reprint/199/1/57 ] ][cite book |last=Gill |first=Frank |year=1995 |title=Ornithology |edition=2nd edition |location=New York |publisher=W.H. Freeman |isbn=0-7167-2415-4|pages=] although the Bar-tailed Godwit is capable of non-stop flights of up to convert|10200|km|mi|-2|abbr=on. [cite news |title=Long-distance Godwit sets new record |url=http://www.birdlife.org/news/news/2007/04/bar-tailed_godwit_journey.html |date=05-04-2007 |publisher=BirdLife International |accessdate=2007-12-13] Seabirds also undertake long migrations, the longest annual migration being those of Sooty Shearwaters, which nest in New Zealand and Chile and spend the northern summer feeding in the North Pacific off Japan, Alaska and California, an annual round trip of convert|64000|km|mi|-2|abbr=on. [cite journal |last=Shaffer |first=Scott A. |coauthors=Yann Tremblay, Henri Weimerskirch "et als" |year=2006 |title=Migratory shearwaters integrate oceanic resources across the Pacific Ocean in an endless summer |journal=Proceedings of the National Academy of Sciences |volume=103 |issue=34 |pages=12799–802 |doi=10.1073/pnas.0603715103 |pmid= 16908846] Other seabirds disperse after breeding, travelling widely but having no set migration route. Albatrosses nesting in the Southern Ocean often undertake circumpolar trips between breeding seasons. [cite journal |last=Croxall |first=John P. |coauthors=Janet R. D. Silk, Richard A. Phillips "et als." |year=2005 |title=Global Circumnavigations: Tracking year-round ranges of nonbreeding Albatrosses |journal=Science |volume=307 |issue=5707 |pages=249–50 |doi=10.1126/science.1106042 |pmid=15653503] Some bird species undertake shorter migrations, travelling only as far as is required to avoid bad weather or obtain food. species such as the boreal finches are one such group and can commonly be found at a location in one year and absent the next. This type of migration is normally associated with food availability. [cite journal |last=Wilson |first=W. Herbert, Jr. |year=1999 |title=Bird feeding and irruptions of northern finches:are migrations short stopped? |journal=North America Bird Bander |volume=24 |issue=4|pages=113–21 |url=http://elibrary.unm.edu/sora/NABB/v024n04/p0113-p0121.pdf] Species may also travel shorter distances over part of their range, with individuals from higher latitudes travelling into the existing range of conspecifics; others undertake partial migrations, where only a fraction of the population, usually females and subdominant males, migrates. [cite journal |last=Nilsson |first=Anna L. K. |coauthors=Thomas Alerstam, and Jan-Åke Nilsson |year=2006 |title=Do partial and regular migrants differ in their responses to weather? |journal=The Auk |volume=123 |issue=2 |pages=537–47 |url=http://findarticles.com/p/articles/mi_qa3793/is_200604/ai_n16410121|doi=10.1642/0004-8038(2006)123 [537:DPARMD] 2.0.CO;2] Partial migration can form a large percentage of the migration behaviour of birds in some regions; in Australia, surveys found that 44% of non-passerine birds and 32% of passerines were partially migratory. [cite journal |last=Chan |first=Ken |year=2001 |title=Partial migration in Australian landbirds: a review |journal=Emu |volume=101 |issue=4 |pages=281–92 |doi=10.1071/MU00034] Altitudinal migration is a form of short distance migration in which birds spend the breeding season at higher altitudes elevations and move to lower ones during suboptimal conditions. It is most often triggered by temperature changes and usually occurs when the normal territories also become inhospitable due to lack of food. [cite journal |last=Rabenold |first=Kerry N. |coauthors=Patricia Parker Rabenold |year=1985 |title=Variation in Altitudinal Migration, Winter Segregation, and Site Tenacity in two subspecies of Dark-eyed Juncos in the southern Appalachians |journal=The Auk|volume=102 |issue=4 |pages=805–19 |url=http://elibrary.unm.edu/sora/Auk/v102n04/p0805-p0819.pdf] Some species may also be nomadic, holding no fixed territory and moving according to weather and food availability. Parrots as a family are overwhelmingly neither migratory nor sedentary but considered to either be dispersive, irruptive, nomadic or undertake small and irregular migrations. [cite book |last=Collar |first=Nigel J. |year=1997|chapter=Family Psittacidae (Parrots)|title=Handbook of the Birds of the World, Volume 4: Sandgrouse to Cuckoos |editor=Josep del Hoyo, Andrew Elliott & Jordi Sargatal (eds.) |location=Barcelona |publisher=Lynx Edicions |isbn=84-87334-22-9|pages=] ]The ability of birds to return to precise locations across vast distances has been known for some time; in an experiment conducted in the 1950s a Manx Shearwater released in Boston returned to its colony in Skomer, Wales within 13 days, a distance of convert|5150|km|mi|-2|abbr=on. [cite journal |last=Matthews |first=G. V. T. |year=1953 |title=Navigation in the Manx Shearwater |journal=Journal of Experimental Biology |volume=30 |issue=2 |pages=370–96 |url=http://jeb.biologists.org/cgi/reprint/30/3/370] Birds navigate during migration using a variety of methods. For diurnal migrants, the sun is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an internal clock.
Communication
Birds communicate using primarily visual and auditory signals. Signals can be interspecific (between species) and intraspecific (within species).
Birds sometimes use plumage to assess and assert social dominance, [cite journal |last=Möller |first=Anders Pape |year=1988 |title=Badge size in the house sparrow "Passer domesticus"|journal=Behavioral Ecology and Sociobiology |volume=22 |issue=5 |pages=373–78 |doi=10.1007/BF00295107 |doi_brokendate= 2008-06-28] to display breeding condition in sexually selected species, or to make threatening displays, as in the Sunbittern's mimicry of a large predator to ward off hawks and protect young chicks. [cite journal |last=Thomas |first=Betsy Trent |coauthors=Stuart D. Strahl |month= |year=1990 |title=Nesting Behavior of Sunbitterns ("Eurypyga helias") in Venezuela |journal=The Condor |volume=92 |issue=3 |pages=576–81 |doi=10.2307/1368675 |url=http://elibrary.unm.edu/sora/Condor/files/issues/v092n03/p0576-p0581.pdf] Variation in plumage also allows for the identification of birds, particularly between species. Visual communication among birds may also involve ritualised displays, which have developed from non-signalling actions such as preening, the adjustments of feather position, pecking, or other behaviour. These displays may signal aggression or submission or may contribute to the formation of pair-bonds.
[
House Wren, a common North American songbird]
Bird calls and songs, which are produced in the syrinx, are the major means by which birds communicate with sound. This communication can be very complex; some species can operate the two sides of the syrinx independently, allowing the simultaneous production of two different songs.[cite journal |last=Miskelly |first=C. M. |coauthors= |month=July |year=1987 |title=The identity of the hakawai |journal=Notornis |volume=34 |issue=2 |pages=95–116 |url=http://www.notornis.org.nz/free_issues/Notornis_34-1987/Notornis_34_2.pdf] woodpeckers drum territorially,][ and Palm Cockatoos use tools to drum. [cite journal |last=Murphy |first=Stephen |coauthors=Sarah Legge and Robert Heinsohn |year=2003 |title=The breeding biology of palm cockatoos ("Probosciger aterrimus"): a case of a slow life history |journal=Journal of Zoology |volume=261 |issue=4 |pages=327–39 |doi=10.1017/S0952836903004175] ]Flocking and other associations
While some birds are essentially territorial or live in small family groups, other birds may form large flocks. The principal benefits of flocking are safety in numbers and increased foraging efficiency.
Birds sometimes also form associations with non-avian species. Plunge-diving seabirds associate with dolphins and tuna, which push shoaling fish towards the surface.[cite journal |last=Au |first=David W. K. |coauthors=Robert L. Pitman |month=August |year=1986 |title=Seabird interactions with Dolphins and Tuna in the Eastern Tropical Pacific |journal=The Condor |volume=88 |issue=3 |pages=304–17 |url=http://elibrary.unm.edu/sora/Condor/files/issues/v088n03/p0304-p0317.pdf |doi=10.2307/1368877|format=PDF] Hornbills have a mutualistic relationship with Dwarf Mongooses, in which they forage together and warn each other of nearby birds of prey and other predators. [cite journal |last=Anne |first=O. |coauthors=E. Rasa |month=June |year=1983 |title=Dwarf mongoose and hornbill mutualism in the Taru desert, Kenya |journal=Behavioral Ecology and Sociobiology |volume=12 |issue=3 |pages=181–90 |doi=10.1007/BF00290770] ]Resting and roosting
The high metabolic rates of birds during the active part of the day is supplemented by rest at other times. Sleeping birds often use a type of sleep known as vigilant sleep, where periods of rest are interspersed with quick eye-opening 'peeks', allowing them to be sensitive to disturbances and enable rapid escape from threats. [cite journal |last=Gauthier-Clerc |first=Michael |coauthors=Alain Tamisier, Frank Cezilly |month=May |year=2000 |title=Sleep-Vigilance Trade-off in Gadwall during the Winter Period |journal=The Condor |volume=102 |issue=2 |pages=307–13 |url=http://elibrary.unm.edu/sora/Condor/files/issues/v102n02/p0307-p0313.pdf |doi=10.1650/0010-5422(2000)102 [0307:SVTOIG] 2.0.CO;2|format=PDF] Swifts have been widely believed to be able to sleep while flying; however, this has not been confirmed by experimental evidence. However, there may be certain kinds of sleep which are possible even when in flight. [cite journal|last=Rattenborg|first=Niels C. |year=2006 |title=Do birds sleep in flight? |journal=Die Naturwissenschaften |volume=93 |issue=9 |pages=413–25 |doi=10.1007/s00114-006-0120-3] Some birds have also demonstrated the capacity to fall into slow-wave sleep one hemisphere of the brain at a time. The birds tend to exercise this ability depending upon its position relative to the outside of the flock. This may allow the eye opposite the sleeping hemisphere to remain vigilant for predators by viewing the outer margins of the flock. This adaptation is also known from marine mammals. [cite journal |last=Milius |first=S. |year=1999 |title=Half-asleep birds choose which half dozes |journal=Science News Online |volume=155 |issue= |pages=86 |url=http://findarticles.com/p/articles/mi_m1200/is_6_155/ai_53965042 |doi=10.2307/4011301] Communal roosting is common because it lowers the loss of body heat and decreases the risks associated with predators. [cite journal |last=Beauchamp |first=Guy |year=1999 |title=The evolution of communal roosting in birds: origin and secondary losses |journal=Behavioural Ecology |volume=10 |issue=6 |pages=675–87 |url=http://beheco.oxfordjournals.org/cgi/content/full/10/6/675 |doi=10.1093/beheco/10.6.675 ] Roosting sites are often chosen with regard to thermoregulation and safety. [cite journal |last=Buttemer |first=William A.|year=1985 |title=Energy relations of winter roost-site utilization by American goldfinches ("Carduelis tristis") |journal=Oecologia |volume=68 |issue=1 |pages=126–32 |url=http://deepblue.lib.umich.edu/dspace/bitstream/2027.42/47760/1/442_2004_Article_BF00379484.pdf |doi=10.1007/BF00379484 |format=|format=PDFdead link|date=August 2008ndash [http://scholar.google.co.uk/scholar?hl=en&lr=&q=author%3AButtemer+intitle%3AEnergy+relations+of+winter+roost-site+utilization+by+American+goldfinches+%28%27%27Carduelis+tristis%27%27%29&as_publication=%5B%5BOecologia%5D%5D&as_ylo=1985&as_yhi=1985&btnG=Search Scholar search] ]
Many sleeping birds bend their heads over their backs and tuck their bills in their back feathers, although others place their beaks among their breast feathers. Many birds rest on one leg, while some may pull up their legs into their feathers, especially in cold weather. Perching birds have a tendon locking mechanism that helps them hold on to the perch when they are asleep. Many ground birds, such as quails and pheasants, roost in trees. A few parrots of the genus "Loriculus" roost hanging upside down. [cite journal |last=Buckley |first=F. G. |coauthors=P. A. Buckley |year=1968 |title=Upside-down Resting by Young Green-Rumped Parrotlets ("Forpus passerinus") |journal=The Condor |volume=70 |issue=1 |pages=89 |doi=10.2307/1366517] Some hummingbirds go into a nightly state of torpor accompanied with a reduction of their metabolic rates. [cite journal |last=Carpenter |first=F. Lynn |year=1974 |title=Torpor in an Andean Hummingbird: Its Ecological Significance |journal=Science |volume=183 |issue=4124 |pages=545–47 |doi=10.1126/science.183.4124.545 |pmid=17773043] This physiological adaptation shows nearly a hundred other species, including owlet-nightjars, nightjars, and woodswallows. One species, the Common Poorwill, even enters a state of hibernation. [cite journal |last=McKechnie |first=Andrew E. |coauthors=Robert A. M. Ashdown, Murray B. Christian and R. Mark Brigham |year=2007 |title=Torpor in an African caprimulgid, the freckled nightjar "Caprimulgus tristigma" |journal=Journal of Avian Biology |volume=38 |issue=3 |pages=261–66 |doi=10.1111/j.2007.0908-8857.04116.x] Birds do not have sweat glands, but they may cool themselves by moving to shade, standing in water, panting, increasing their surface area, fluttering their throat or by using special behaviours like urohydrosis to cool themselves.
Breeding
ocial systems
Ninety-five percent of bird species are socially monogamous. These species pair for at least the length of the breeding season or—in some cases—for several years or until the death of one mate. [cite journal|last=Freed|first=Leonard A.|year=1987|title=The Long-Term Pair Bond of Tropical House Wrens: Advantage or Constraint?|journal=The American Naturalist|volume=130|issue=4|pages=507–25|doi=10.1086/284728] Monogamy allows for biparental care, which is especially important for species in which females require males' assistance for successful brood-rearing. [cite journal|last=Gowaty|first=Patricia A.|title=Male Parental Care and Apparent Monogamy among Eastern Bluebirds("Sialia sialis")|journal=The American Naturalist|volume=121|issue=2|pages=149–60|year=1983|doi=10.1086/284047] Among many socially monogamous species, extra-pair copulation (infidelity) is common. [cite journal|last=Westneat|first=David F.|coauthors=Ian R. K. Stewart|year=2003|title=Extra-pair paternity in birds: Causes, correlates, and conflict|url=http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.ecolsys.34.011802.132439 |doi=10.1146/annurev.ecolsys.34.011802.132439 |journal=Annual Review of Ecology, Evolution, and Systematics|volume=34|pages=365–96] Such behaviour typically occurs between dominant males and females paired with subordinate males, but may also be the result of forced copulation in ducks and other anatids. [cite journal|last=Gowaty|first=Patricia A.|coauthors=Nancy Buschhaus|year=1998|url=http://findarticles.com/p/articles/mi_qa3746/is_199802/ai_n8791262|title=Ultimate causation of aggressive and forced copulation in birds: Female resistance, the CODE hypothesis, and social monogamy|journal=American Zoologist|volume=38|issue=1|pages=207–25|doi=10.1093/icb/38.1.207] For females, possible benefits of extra-pair copulation include getting better genes for her offspring and insuring against the possibility of infertility in her mate. [cite journal|last=Sheldon|first=B|year=1994|title=Male Phenotype, Fertility, and the Pursuit of Extra-Pair Copulations by Female Birds|journal=Proceedings: Biological Sciences|volume=257|issue=1348|pages=25–30|doi=10.1098/rspb.1994.0089] Males of species that engage in extra-pair copulations will closely guard their mates to ensure the parentage of the offspring that they raise. [cite journal|last=Wei|first=G|coauthors=Z Yin, F Lei|year=2005|title=Copulations and mate guarding of the Chinese Egret |doi=10.1675/1524-4695(2005)28 [527:CAMGOT] 2.0.CO;2 |journal=Waterbirds|volume=28|issue=4|pages=527–30]
Other mating systems, including polygyny, polyandry, polygamy, polygynandry, and promiscuity, also occur.
Breeding usually involves some form of courtship display, typically performed by the male. [cite book|last=Short|first=Lester L.|year=1993|title=Birds of the World and their Behavior|publisher=Henry Holt and Co|location=New York|isbn=0-8050-1952-9] Most displays are rather simple and involve some type of song. Some displays, however, are quite elaborate. Depending on the species, these may include wing or tail drumming, dancing, aerial flights, or communal lekking. Females are generally the ones that drive partner selection, [cite book|last=Burton|first=R|year=1985|title=Bird Behavior|publisher=Alfred A. Knopf, Inc.|isbn=0-394-53857-5] although in the polyandrous phalaropes, this is reversed: plainer males choose brightly coloured females. [cite journal|last=Schamel|first=D|coauthors=DM Tracy, DB Lank, DF Westneat|year=2004|title=Mate guarding, copulation strategies and paternity in the sex-role reversed, socially polyandrous red-necked phalarope "Phalaropus lobatus"|journal=Behaviour Ecology and Sociobiology|volume=57|issue=2|pages=110–18|url=http://www.springerlink.com/index/8BE48GKGYF2Q40LT.pdf|doi=10.1007/s00265-004-0825-2|format=PDF] Courtship feeding, billing and allopreening are commonly performed between partners, generally after the birds have paired and mated.Territories, nesting and incubation
Many birds actively defend a territory from others of the same species during the breeding season; maintenance of territories protects the food source for their chicks. Species that are unable to defend feeding territories, such as seabirds and swifts, often breed in colonies instead; this is thought to offer protection from predators. Colonial breeders defend small nesting sites, and competition between and within species for nesting sites can be intense. [Kokko H, Harris M, Wanless S (2004). "Competition for breeding sites and site-dependent population regulation in a highly colonial seabird, the common guillemot "Uria aalge"." "Journal of Animal Ecology" 73 (2): 367–76. DOI|10.1111/j.0021-8790.2004.00813.x]
All birds lay amniotic eggs with hard shells made mostly of calcium carbonate.
Bird eggs are usually laid in a nest. Most species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows.[Hansell M (2000). "Bird Nests and Construction Behaviour". University of Cambridge Press ISBN 0-521-46038-7] Some bird nests, however, are extremely primitive; albatross nests are no more than a scrape on the ground. Most birds build nests in sheltered, hidden areas to avoid predation, but large or colonial birds—which are more capable of defence—may build more open nests. During nest construction, some species seek out plant matter from plants with parasite-reducing toxins to improve chick survival, [Lafuma L, Lambrechts M, Raymond M (2001). "Aromatic plants in bird nests as a protection against blood-sucking flying insects?" "Behavioural Processes" 56 (2) 113–20. DOI|10.1016/S0376-6357(01)00191-7] and feathers are often used for nest insulation.]Incubation, which optimises temperature for chick development, usually begins after the last egg has been laid.
Parental care and fledging
At the time of their hatching, chicks range in development from helpless to independent, depending on their species. Helpless chicks are termed "altricial", and tend to be born small, blind, immobile and naked; chicks that are mobile and feathered upon hatching are termed "precocial". Altricial chicks need help thermoregulating and must be brooded for longer than precocial chicks. Chicks at neither of these extremes can be semi-precocial or semi-altricial.
The length and nature of parental care varies widely amongst different orders and species. At one extreme, parental care in megapodes ends at hatching; the newly-hatched chick digs itself out of the nest mound without parental assistance and can fend for itself immediately. [Elliot A (1994). "Family Megapodiidae (Megapodes)" in "Handbook of the Birds of the World. Volume 2; New World Vultures to Guineafowl" (eds del Hoyo J, Elliott A, Sargatal J) Lynx Edicions:Barcelona. ISBN 84-873337-15-6 ] At the other extreme, many seabirds have extended periods of parental care, the longest being that of the Great Frigatebird, whose chicks take up to six months to fledge and are fed by the parents for up to an additional 14 months. [Metz VG, Schreiber EA (2002). "Great Frigatebird ("Fregata minor")" In "The Birds of North America, No 681", (Poole, A. & Gill, F., eds) The Birds of North America Inc: Philadelphia ] In some species, both parents care for nestlings and fledglings; in others, such care is the responsibility of only one sex. In some species, other members of the same species—usually close relatives of the breeding pair, such as offspring from previous broods—will help with the raising of the young. [Ekman J (2006). "Family living amongst birds." "Journal of Avian Biology" 37 (4): 289–98. DOI|10.1111/j.2006.0908-8857.03666.x] Such alloparenting is particularly common among the Corvida, which includes such birds as the true crows, Australian Magpie and Fairy-wrens, [cite book |author=Cockburn A|editor=Floyd R, Sheppard A, de Barro P|title=Frontiers in Population Ecology|year=1996|publisher=CSIRO|location=Melbourne|isbn= |pages=21–42|chapter=Why do so many Australian birds cooperate? Social evolution in the Corvida] but has been observed in species as different as the Rifleman and Red Kite. Among most groups of animals, male parental care is rare. In birds, however, it is quite common—more so than in any other vertebrate class.
The point at which chicks fledge varies dramatically. The chicks of the "Synthliboramphus" murrelets, like the Ancient Murrelet, leave the nest the night after they hatch, following their parents out to sea, where they are raised away from terrestrial predators. [Gaston AJ (1994). Ancient Murrelet ("Synthliboramphus antiquus"). In "The Birds of North America, No. 132" (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington, D.C.: The American Ornithologists' Union.] Some other species, such as ducks, move their chicks away from the nest at an early age. In most species, chicks leave the nest just before, or soon after, they are able to fly. The amount of parental care after fledging varies; albatross chicks leave the nest on their own and receive no further help, while other species continue some supplementary feeding after fledging. [Schaefer HC, Eshiamwata GW, Munyekenye FB, Bohning-Gaese K (2004). "Life-history of two African "Sylvia" warblers: low annual fecundity and long post-fledging care." "Ibis" 146 (3): 427–37. DOI|10.1111/j.1474-919X.2004.00276.x] Chicks may also follow their parents during their first migration. [ Alonso JC, Bautista LM, Alonso JA (2004). "Family-based territoriality vs flocking in wintering common cranes "Grus grus"." "Journal of Avian Biology" 35 (5): 434–44. DOI|10.1111/j.0908-8857.2004.03290.x]
Brood parasites
Brood parasitism, in which an egg-layer leaves her eggs with another individual's brood, is more common among birds than any other type of organism.[Davies N (2000). "Cuckoos, Cowbirds and other Cheats". T. & A. D. Poyser: London ISBN 0-85661-135-2] After a parasitic bird lays her eggs in another bird's nest, they are often accepted and raised by the host at the expense of the host's own brood. Brood parasites may be either "obligate brood parasites", which must lay their eggs in the nests of other species because they are incapable of raising their own young, or "non-obligate brood parasites", which sometimes lay eggs in the nests of conspecifics to increase their reproductive output even though they could have raised their own young. [Sorenson M (1997). "Effects of intra- and interspecific brood parasitism on a precocial host, the canvasback, "Aythya valisineria"." "Behavioral Ecology" 8 (2) 153–61. [http://beheco.oxfordjournals.org/cgi/reprint/8/2/153.pdf PDF] ] One hundred bird species, including honeyguides, icterids, estrildid finches and ducks, are obligate parasites, though the most famous are the cuckoos.]Ecology
[
South Polar Skua (left) is a generalist predator, taking the eggs of other birds, fish, carrion and other animals. This skua is attempting to push an Adelie Penguin (right) off its nest] Birds occupy a wide range of ecological positions.
Some nectar-feeding birds are important pollinators, and many frugivores play a key role in seed dispersal.[Clout M, Hay J (1989). "The importance of birds as browsers, pollinators and seed dispersers in New Zealand forests." "New Zealand Journal of Ecology" 12 27–33 [http://www.newzealandecology.org/nzje/free_issues/NZJEcol12_s_27.pdf PDF] ] Plants and pollinating birds often coevolve, [Stiles F (1981). "Geographical Aspects of Bird–Flower Coevolution, with Particular Reference to Central America." "Annals of the Missouri Botanical Garden" 68 (2) 323–51. DOI|10.2307/2398801] and in some cases a flower's primary pollinator is the only species capable of reaching its nectar. [Temeles E, Linhart Y, Masonjones M, Masonjones H (2002). "The Role of Flower Width in Hummingbird Bill Length–Flower Length Relationships." "Biotropica" 34 (1): 68–80. [http://www.amherst.edu/~ejtemeles/Temeles%20et%20al%202002%20biotropica.pdf PDF] ] ]Birds are often important to island ecology. Birds have frequently reached islands that mammals have not; on those islands, birds may fulfill ecological roles typically played by larger animals. For example, in New Zealand the moas were important browsers, as are the Kereru and Kokako today.
Avian ecology field methods are used for researching avian ecology.
Relationship with humans
Since birds are highly visible and common animals, humans have had a relationship with them since the dawn of man. [citation|last=Bonney|first=Rick | last2 = Rohrbaugh, Jr.| first2 = Ronald|title=Handbook of Bird Biology| place= Princeton, NJ|publisher=Princeton University Press|year=2004| edition = Second|isbn=0-938-02762-X] Sometimes, these relationships are mutualistic, like the cooperative honey-gathering among honeyguides and African peoples such as the Borana. [Dean W, Siegfried R, MacDonald I (1990). "The Fallacy, Fact, and Fate of Guiding Behavior in the Greater Honeyguide." "Conservation Biology" 4 (1) 99–101. [http://www.blackwell-synergy.com/doi/abs/10.1111/j.1523-1739.1990.tb00272.x PDF] ] Other times, they may be commensal, as when species such as the House Sparrow [Singer R, Yom-Tov Y (1988). "The Breeding Biology of the House Sparrow "Passer domesticus" in Israel." "Ornis Scandinavica" 19 139–44. DOI|10.2307/3676463] have benefited from human activities. Several bird species have become commercially significant agricultural pests, [Dolbeer R (1990). "Ornithology and integrated pest management: Red-winged blackbirds "Agleaius phoeniceus" and corn." "Ibis" 132 (2): 309–22.] and some pose an aviation hazard. [Dolbeer R, Belant J, Sillings J (1993). "Shooting Gulls Reduces Strikes with Aircraft at John F. Kennedy International Airport." "Wildlife Society Bulletin " 21: 442–50. ] Human activities can also be detrimental, and have threatened numerous bird species with extinction.
Birds can act as vectors for spreading diseases such as psittacosis, salmonellosis, campylobacteriosis, mycobacteriosis (avian tuberculosis), avian influenza (bird flu), giardiasis, and cryptosporidiosis over long distances. Some of these are zoonotic diseases that can also be transmitted to humans. [Reed KD, Meece JK, Henkel JS, Shukla SK (2003). [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1069015 "Birds, Migration and Emerging Zoonoses: West Nile Virus, Lyme Disease, Influenza A and Enteropathogens."] Clin Med Res. 1 (1):5–12. PMID 15931279 ]
Economic importance
Domesticated birds raised for meat and eggs, called poultry, are the largest source of animal protein eaten by humans; in 2003, 76 million tons of poultry and 61 million tons of eggs were produced worldwide. [ [http://www.earth-policy.org/Books/Out/Ote3_3.htm Shifting protein sources: Chapter 3: Moving Up the Food Chain Efficiently.] Earth Policy Institute. Retrieved on December 18, 2007.] Chickens account for much of human poultry consumption, though turkeys, ducks, and geese are also relatively common. Many species of birds are also hunted for meat. Bird hunting is primarily a recreational activity except in extremely undeveloped areas. The most important birds hunted in North and South America are waterfowl; other widely hunted birds include pheasants, wild turkeys, quail, doves, partridge, grouse, snipe, and woodcock. [Simeone A, Navarro X (2002). [http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2002000200012&lng=es&nrm=iso&tlng=en "Human exploitation of seabirds in coastal southern Chile during the mid-Holocene."] "Rev. chil. hist. nat" 75 (2): 423–31 ] Muttonbirding is also popular in Australia and New Zealand. [Hamilton S (2000). "How precise and accurate are data obtained using. an infra-red scope on burrow-nesting sooty shearwaters "Puffinus griseus"?" "Marine Ornithology" 28 (1): 1–6 [http://www.marineornithology.org/PDF/28_1/28_1_1.pdf PDF] ] Though some hunting, such as that of muttonbirds, may be sustainable, hunting has led to the extinction or endangerment of dozens of species. [ Keane A, Brooke MD, Mcgowan PJK (2005). "Correlates of extinction risk and hunting pressure in gamebirds (Galliformes)." "Biological Conservation" 126 (2): 216–33. DOI|10.1016/j.biocon.2005.05.011]
Other commercially valuable products from birds include feathers (especially the down of geese and ducks), which are used as insulation in clothing and bedding, and seabird feces (guano), which is a valuable source of phosphorus and nitrogen. The War of the Pacific, sometimes called the Guano War, was fought in part over the control of guano deposits. [ [http://www.zum.de/whkmla/military/19cen/guanowar.html The Guano War of 1865-1866.] World History at KMLA. Retrieved on December 18, 2007.]
Birds have been domesticated by humans both as pets and for practical purposes. Colourful birds, such as parrots and mynas, are bred in captivity or kept as pets, a practice that has led to the illegal trafficking of some endangered species. [Cooney R, Jepson P (2006). "The international wild bird trade: what's wrong with blanket bans?" "Oryx" 40 (1): 18–23. [http://journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=409231 PDF] ] Falcons and cormorants have long been used for hunting and fishing, respectively. Messenger pigeons, used since at least 1 AD, remained important as recently as World War II. Today, such activities are more common either as hobbies, for entertainment and tourism, [Manzi M (2002). [http://findarticles.com/p/articles/mi_go1895/is_200210/ai_n8674873 "Cormorant fishing in Southwestern China: a Traditional Fishery under Siege. (Geographical Field Note)."] "Geographic Review" 92 (4): 597–603.] or for sports such as pigeon racing.
Amateur bird enthusiasts (called birdwatchers, twitchers or, more commonly, birders) number in the millions. [Pullis La Rouche, G. (2006). Birding in the United States: a demographic and economic analysis. "Waterbirds around the world." Eds. G.C. Boere, C.A. Galbraith & D.A. Stroud. The Stationery Office, Edinburgh, UK. pp. 841–46. [http://www.jncc.gov.uk/PDF/pub07_waterbirds_part6.2.5.pdf PDF] ] Many homeowners erect bird feeders near their homes to attract various species. Bird feeding has grown into a multimillion dollar industry; for example, an estimated 75% of households in Britain provide food for birds at some point during the winter. [Chamberlain DE, Vickery JA, Glue DE, Robinson RA, Conway GJ, Woodburn RJW, Cannon AR (2005). "Annual and seasonal trends in the use of garden feeders by birds in winter." "Ibis" 147 (3): 563–75. [http://www.blackwell-synergy.com/doi/pdf/10.1111/j.1474-919x.2005.00430.x PDF] ]
Religion, folklore and culture
Birds play prominent and diverse roles in folklore, religion, and popular culture. In religion, birds may serve as either messengers or priests and leaders for a deity, such as in the Cult of Makemake, in which the Tangata manu of Easter Island served as chiefs, [Routledge S, Routledge K (1917). "The Bird Cult of Easter Island." "Folklore" 28 (4): 337–55.] or as attendants, as in the case of Hugin and Munin, two Common Ravens who whispered news into the ears of the Norse god Odin. [Chappell J (2006). [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1326277 "Living with the Trickster: Crows, Ravens, and Human Culture."] "PLoS Biol" 4 (1):e14. DOI|10.1371/journal.pbio.0040014] They may also serve as religious symbols, as when Jonah (Hebrew: יוֹנָה, dove) embodied the fright, passivity, mourning, and beauty traditionally associated with doves. [Hauser A (1985). "Jonah: In Pursuit of the Dove." "Journal of Biblical Literature" 104 (1): 21–37. DOI|10.2307/3260591] Birds have themselves been deified, as in the case of the Common Peacock, which is perceived as Mother Earth by the Dravidians of India. [Nair P (1974). "The Peacock Cult in Asia." "Asian Folklore Studies" 33 (2): 93–170. DOI|10.2307/1177550] Some birds have also been perceived as monsters, including the mythological Roc and the Māori's legendary "Pouākai", a giant bird capable of snatching humans. [Tennyson A, Martinson P (2006). "Extinct Birds of New Zealand" Te Papa Press, Wellington ISBN 978-0-909010-21-8]
Birds have been featured in culture and art since prehistoric times, when they were represented in early cave paintings. [Meighan C (1966). "Prehistoric Rock Paintings in Baja California." "American Antiquity" 31 (3): 372–92. DOI|10.2307/2694739] Birds were later used in religious or symbolic art and design, such as the magnificent Peacock Throne of the Mughal and Persian emperors. [Clarke CP (1908). "A Pedestal of the Platform of the Peacock Throne." "The Metropolitan Museum of Art Bulletin" 3 (10): 182–83. DOI|10.2307/3252550] With the advent of scientific interest in birds, many paintings of birds were commissioned for books. Among the most famous of these bird artists was John James Audubon, whose paintings of North American birds were a great commercial success in Europe and who later lent his name to the National Audubon Society. [Boime A (1999). "John James Audubon, a birdwatcher's fanciful flights." "Art History" 22 (5) 728–55. DOI|10.1111/1467-8365.00184] Birds are also important figures in poetry; for example, Homer incorporated Nightingales into his "Odyssey", and Catullus used a sparrow as an erotic symbol in his Catullus 2. [Chandler A (1934). "The Nightingale in Greek and Latin Poetry." "The Classical Journal" 30 (2): 78–84. ] The relationship between an albatross and a sailor is the central theme of Samuel Taylor Coleridge's The Rime of the Ancient Mariner, which led to the use of the term as a metaphor for a 'burden'. [Lasky E (1992). "A Modern Day Albatross: The Valdez and Some of Life's Other Spills." "The English Journal", 81 (3): 44–46. DOI|10.2307/820195] Other English metaphors derive from birds; vulture funds and vulture investors, for instance, take their name from the scavenging vulture. [Carson A (1998). "Vulture Investors, Predators of the 90s: An Ethical Examination." "Journal of Business Ethics" 17 (5): 543–55. [http://www.springerlink.com/index/W676R8803NL06L38.pdf PDF] ]
Perceptions of various bird species often vary across cultures. Owls are associated with bad luck, witchcraft, and death in parts of Africa, [Enriquez PL, Mikkola H (1997). "Comparative study of general public owl knowledge in Costa Rica, Central America and Malawi, Africa." Pp. 160–66 In: J.R. Duncan, D.H. Johnson, T.H. Nicholls, (Eds). "Biology and conservation of owls of the Northern Hemisphere. General Technical Report NC-190", USDA Forest Service, St. Paul, Minnesota. 635 pp.] but are regarded as wise across much of Europe. [Lewis DP (2005). [http://www.owlpages.com/articles.php?section=Owl+Mythology&title=Myth+and+Culture Owls in Mythology and Culture.] The Owl Pages. Retrieved on September 15, 2007.] Hoopoes were considered sacred in Ancient Egypt and symbols of virtue in Persia, but were thought of as thieves across much of Europe and harbingers of war in Scandinavia. [Dupree N (1974). "An Interpretation of the Role of the Hoopoe in Afghan Folklore and Magic." "Folklore" 85 (3): 173–93.]
Conservation
Though human activities have allowed the expansion of a few species, such as the Barn Swallow and European Starling, they have caused population decreases or extinction in many other species. Over a hundred bird species have gone extinct in historical times, [Fuller E (2000). "Extinct Birds" (2nd ed.). Oxford University Press, Oxford, New York. ISBN 0-19-850837-9] although the most dramatic human-caused avian extinctions, eradicating an estimated 750–1800 species, occurred during the human colonisation of Melanesian, Polynesian, and Micronesian islands. [Steadman D (2006). "Extinction and Biogeography in Tropical Pacific Birds", University of Chicago Press. ISBN 978-0-226-77142-7] Many bird populations are declining worldwide, with 1,221 species listed as threatened by Birdlife International and the IUCN in 2007. [Birdlife International (2007). [http://www.birdlife.org/news/news/2007/05/2007_red_list_update.html 1,221 and counting: More birds than ever face extinction.] Retrieved on 3 June 2007.] The most commonly cited human threat to birds is habitat loss. [Norris K, Pain D (eds) (2002). "Conserving Bird Biodiversity: General Principles and their Application" Cambridge University Press. ISBN 978-0521789493] Other threats include overhunting, accidental mortality due to structural collisions or long-line fishing bycatch, [Brothers NP (1991). "Albatross mortality and associated bait loss in the Japanese longline fishery in the southern ocean." "Biological Conservation" 55: 255–68.] pollution (including oil spills and pesticide use), [Wurster D, Wurster C, Strickland W (1965). "Bird Mortality Following DDT Spray for Dutch Elm Disease." "Ecology" 46 (4): 488–99. DOI|10.1126/science.148.3666.90] competition and predation from nonnative invasive species, [Blackburn T, Cassey P, Duncan R, Evans K, Gaston K (2004). "Avian Extinction and Mammalian Introductions on Oceanic Islands." "Science" 305: 1955–58. DOI|10.1126/science.1101617] and climate change. Governments and conservation groups work to protect birds, either by passing laws that preserve and restore bird habitat or by establishing captive populations for reintroductions. Such projects have produced some successes; one study estimated that conservation efforts saved 16 species of bird that would otherwise have gone extinct between 1994 and 2004, including the California Condor and Norfolk Island Green Parrot. [Butchart S, Stattersfield A, Collar N (2006). "How many bird extinctions have we prevented?" "Oryx" 40 (3): 266–79 [http://www.birdlife.org/news/news/2006/08/butchart_et_al_2006.pdf PDF] ]
References
External links
* [http://www.bsc-eoc.org/avibase/avibase.jsp?lang=EN&pg=home Avibase] – The World Bird Database
* [http://www.birdlife.org/ Birdlife International] – Dedicated to bird conservation worldwide; has a database with about 250,000 records on endangered bird species.
* [http://people.eku.edu/ritchisong/birdbiogeography1.htm Bird biogeography]
* [http://www.audubon.org/bird/index.html Birds and Science] from the National Audubon Society
* [http://www.birds.cornell.edu/ Cornell Lab of Ornithology]
* [http://www.stanford.edu/group/stanfordbirds/text/essays/completed_essays.html Essays on bird biology]
* [http://www.i-o-c.org/IOComm/index.htm International Ornithological Committee]
* [http://www.mrnussbaum.com/birdsindex.htm North American Birds for Kids]
* [http://www.ornithology.com/ Ornithology]
* [http://elibrary.unm.edu/sora/index.php Sora] Searchable online research archive; Archives of the following ornithological journals The Auk, Condor, Journal of Field Ornithology, North American Bird Bander, Studies in Avian Biology, Pacific Coast Avifauna, and the Wilson Bulletin.
* [http://www.hbw.com/ibc/ The Internet Bird Collection] – A free library of videos of the world's birds
* [http://www.birdpop.org/ The Institute for Bird Populations, California]
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