Bird: Difference between revisions

Birds; Temporal range: Late Jurassic - Recent
	Superb Fairy-wren, Malurus cyaneus, juvenile
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Aves; Linnaeus, 1758
Orders
	Many - see section below.

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Birds are bipedal, warm-blooded, oviparous vertebrate animals characterized primarily by feathers, forelimbs modified as wings, and (in most) hollow bones. All birds reproduce sexually, although parthenogenetic eggs are known to be produced by the domesticated turkey on occasion and are suspected to occur in its wild ancestor.[1]

Birds range in size from the tiny hummingbirds to the huge Ostrich and Emu. Depending on the taxonomic viewpoint, there are about 8,800–10,200 living bird species (and about 120–130 that have become extinct in the span of human history) in the world, making them the most diverse class of terrestrial vertebrates.

Birds feed on a variety of materials, including nectar, plants, seeds, carrion, and various types of small animals including other birds.

Most birds are diurnal, or active during the day, 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.

Common characteristics of birds include beak with no teeth, the laying of hard-shelled eggs, high metabolic rate, a four-chambered heart, and a light but strong skeleton. Most birds are characterized by flight, though the ratites are flightless, and several others, particularly endemic island species, have also lost this ability.

Birds are among the most extensively studied of all animal groups. The scientific study of birds is called ornithology. Hundreds of academic journals and thousands of scientists are devoted to bird research, while amateur enthusiasts (called birdwatchers, twitchers or, more commonly, birders) probably number in the millions.

High-level taxonomy

The first classification of birds was developed by Francis Willughby and John Ray with their volume Ornithologiae written in 1676.^[1] That work, slightly modified, was the basis for today's classification system originally devised by Linneus in 1758.

Birds are categorized as a biological class, Aves. The earliest known species of this class is Archaeopteryx lithographica, from the Late Jurassic period. Modern phylogenies place birds in the dinosaur clade Theropoda. According to the current consensus, Aves and a sister group, the order Crocodilia, together are the sole living members of an unranked "reptile" clade, the Archosauria.

Phylogenetically, Aves is usually defined as all descendants of the most recent common ancestor of modern birds (or of a specific modern bird species like Passer domesticus), and Archaeopteryx.

Modern birds are divided into two superorders, the Paleognathae (mostly flightless birds like ostriches), and the wildly diverse Neognathae, containing all other birds.

Bird orders

This is a list of the taxonomic orders in the subclass Neornithes, or modern birds. The list of birds gives a more detailed summary of these, including families.

SUBCLASS NEORNITHES
Paleognathae:

Struthioniformes, Ostrich, emus, kiwis, and allies
Tinamiformes, tinamous

Neognathae:

Anseriformes, waterfowl
Galliformes, fowl
Gaviiformes, loons
Podicipediformes, grebes
Procellariiformes, albatrosses, petrels, and allies
Sphenisciformes, penguins
Pelecaniformes, pelicans and allies
Ciconiiformes, storks and allies
Phoenicopteriformes, flamingos
Falconiformes, falcons, eagles, hawks and allies
Gruiformes, cranes and allies
Charadriiformes, gulls, button-quail, plovers and allies
Pteroclidiformes, sandgrouse
Columbiformes, doves and pigeons
Psittaciformes, parrots and allies
Cuculiformes, cuckoos, turacos, hoatzin
Strigiformes, owls
Caprimulgiformes, nightjars and allies
Apodiformes, swifts and hummingbirds
Coraciiformes, kingfishers
Piciformes, woodpeckers and allies
Trogoniformes, trogons
Coliiformes, mousebirds
Passeriformes, passerines

Note: This is the traditional classification (the so-called Clements order). A radically different classification based on molecular data has been developed (the so-called Sibley-Monroe classification or Sibley-Ahlquist taxonomy). This has influenced taxonomic thinking considerably, with the Galloanserae proving well-supported by recent molecular, fossil and anatomical evidence.^{[citation needed]} With increasingly good evidence, it has become possible by 2006 to test the major proposals of the Sibley-Ahlquist taxonomy. The results are often nothing short of astounding, see e.g. Charadriiformes or Caprimulgiformes.

Extinct bird orders

A wide variety of extinct bird groups occurred during the Mesozoic era and left no modern descendants. These include the orders Archaeopterygiformes, Confuciusornithiformes, toothed seabirds like the Hesperornithes and Ichthyornithes, and the diverse subclass Enantiornithes ("opposite birds").

For a complete listing of prehistoric bird groups, see Fossil birds and Late Quaternary prehistoric birds.

Evolution

There is significant evidence that birds evolved from theropod dinosaurs, specifically, that birds are members of Maniraptora, a group of theropods which includes dromaeosaurs and oviraptorids, among others.^[2] As more non-avian theropods that are closely related to birds are discovered, the formerly clear distinction between non-birds and birds becomes less so. Recent discoveries in northeast China (Liaoning Province), demonstrating that many small theropod dinosaurs had feathers, contribute to this ambiguity.

The basal bird Archaeopteryx, from the Jurassic, is well-known as one of the first "missing links" to be found in support of evolution in the late 19th century, though it is not considered a direct ancestor of modern birds. Confuciusornis is another early bird; it lived in the Early Cretaceous. Both may be predated by Protoavis texensis, though the fragmentary nature of this fossil leaves it open to considerable doubt if this was a bird ancestor. Other Mesozoic birds include the Enantiornithes, Yanornis, Ichthyornis, Gansus and the Hesperornithiformes, a group of flightless divers resembling grebes and loons.

The recently (2002) discovered dromaeosaur Cryptovolans was capable of powered flight, possessed a sternal keel and had ribs with uncinate processes. In fact, Cryptovolans makes a better "bird" than Archaeopteryx which is missing some of these modern bird features. Because of this, some paleontologists have suggested that dromaeosaurs are actually basal birds whose larger members are secondarily flightless, i.e. that dromaeosaurs evolved from birds and not the other way around. Evidence for this theory is currently inconclusive, but digs continue to unearth fossils (especially in China) of the strange feathered dromaeosaurs. At any rate, it is fairly certain that avian flight existed in the mid-Jurassic and was "tried out" in several lineages and variants by the mid-Cretaceous.

Although ornithischian (bird-hipped) dinosaurs share the same hip structure as birds, birds actually originated from the saurischian (lizard-hipped) dinosaurs (if the dinosaurian origin theory is correct), and thus arrived at their hip structure condition independently. In fact, the bird-like hip structure also developed a third time among a peculiar group of theropods, the Therizinosauridae.

An alternate theory to the dinosaurian origin of birds, espoused by a few scientists (most notably Lary Martin and Alan Feduccia), states that birds (including maniraptoran "dinosaurs") evolved from early archosaurs like Longisquama, a theory which is contested by most other scientists in paleontology, and by experts in feather development and evolution such as R.O. Prum. See the Longisquama article for more on this alternative.

Modern birds are classified in Neornithes, which are now known to have evolved into some basic lineages by the end of the Cretaceous (see Vegavis). The Neornithes are split into the Paleognathae and Neognathae. The paleognaths include the tinamous (found only in Central and South America) and the ratites. The ratites are large flightless birds, and include ostriches, cassowaries, kiwis and emus (though some scientists suspect that the ratites represent an artificial grouping of birds which have independently lost the ability to fly in a number of unrelated lineages). The basal divergence from the remaining Neognathes was that of the Galloanseri, the superorder containing the Anseriformes (ducks, geese and swans), and the Galliformes (the pheasants, grouse, and their allies). See the chart for more information.

The classification of birds is a contentious issue. Sibley & Ahlquist's Phylogeny and Classification of Birds (1990) is a landmark work on the classification of birds (although frequently debated and constantly revised). A preponderance of evidence seems to suggest that the modern bird orders constitute accurate taxa. However, scientists are not in agreement as to the relationships between the orders; 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. See also: Sibley-Ahlquist taxonomy and dinosaur classification.

Bird anatomy

Birds have a body plan that shows so many unusual adaptations (mostly aiding flight) that birds have earned their own unique class in the chordate phylum.

The skeleton consists of bones which are very light. They have large pneumatic cavities which connect with the respiratory system. The skull bones are fused and do not show cranial sutures. 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. The last few are fused with the pelvis to form the synsacrum. The ribs are flattened and the sternum is keeled for the attachment of flight muscles, except in the flightless bird orders. The forelimbs are modified into the wings.

Unlike mammals, birds do not urinate. Their kidneys extract nitrogenous wastes from the bloodstream, but instead of excreting it as urea dissolved in urine, they excrete it in the form of uric acid. They also excrete creatine rather than creatinine as in mammals. Uric acid has a very low solubility in water, so it emerges as a white paste. This material, as well as the output of the intestines, emerges from the bird's cloaca. The cloaca is a multi-purpose hole for birds: their wastes come out of it, they mate by joining cloaca, and females lay eggs out of it. In addition, many species of birds regurgitate pellets.

Birds have one of the most complex lung systems of all organisms. Air enters the bird and immediately 75% of the air bypasses the lungs and flows directly into a posterior air sac which extends from the lungs and connects with air spaces in the bones and fills them with air. When the bird exhales, the air from the posterior air sac is forced into the lungs; thus birds receive a supply of air during both inhalation and exhalation. The gas exchange then takes place in the capillaries. The heart has four chambers and the right aortic arch gives rise to systemic aorta (unlike in the mammals where the left arch is involved). Postcava receives blood from the limbs via the renal portal system. Birds, unlike mammals, have nucleated erythrocytes, i.e. red blood cells which retain a nucleus.

Sound production is achieved using the syrinx, a muscular chamber with several tympanic membranes, situated at the lower end of the trachea where it bifurcates.

The digestive system of the bird is unique and has a crop for storage and a gizzard for grinding food. Most are highly adapted for rapid digestion, an adaptation to flight. Migratory birds have the additional ability to reduce parts of the intestines prior to migration.

The nervous system, relative to the bird's size, is actually quite large. The most developed part of the brain is the one that controls the flight related function while the cerebellum coordinates movement and the cerebrum controls behavior patterns, navigation, mating and nest building. A bird’s eyes are developed for taking off, spotting landmarks, hunting and feeding. Birds with eyes on the sides of their heads have a wide visual field while birds with eyes on the front of their heads like owls have binocular vision and can measure depth.

Most birds have a poor sense of smell except for the kiwis, the vultures and the tubenoses. The visual system is highly developed. Water birds have special flexible lenses, allowing accommodation for vision in air and water. Some species also have dual fovea. The bird retina has a fan shaped blood supply system called the pecten. The avian ear lacks external pinnae but is covered by feathers. The inner ear has a cochlea but it is not spiral as in mammals.

Some birds use chemical defenses against predators. Tubenoses can eject an unpleasant oil against an aggressor, and some species of pitohui, found in New Guinea, secrete a powerful neurotoxin in their skin and feathers.

Feathers and plumage

The characteristic that distinguishes the birds from all other living groups is the covering of feathers. Feathers are epidermal growths attached to the skin that serve a variety of functions to birds, they aid in thermoregulation by insulating birds from cold weather and water; they are essential to bird flight and are also used in display, camouflage and signalling. There are several different types of feather that serve different purposes. Feathers need maintenance, and birds preen or groom their feathers, using their bills to brush away foreign particles. The arrangement and appearance of feathers on the body is known as plumage.

Bird Flight and Migration

Flight in vertebrates is mostly particular to birds, although mammalian bats also fly and about 40 species of birds are flightless. It is the main means of locomotion for most avian species. Flight in birds is used for breeding, feeding, and predator avoidance and escape. Wing shape and size primarily determines the type of flight each species is capable of.

Many bird species migrate to take advantage of global differences of seasonal temperatures to optimize availability of food sources and breeding habitat. There are two primary types of migration. Long distance bird migration is usually triggered by length of daylight. It is characterized by species spending the warmer breeding season in temperate or arctic/antarctic regions, and the colder non breeding season in the tropical regions. Many birds substantially increase body fats and reserves to endure the rigors of these long flights. These reserves are most often entirely used up by the end of the particular birds migration route. Fallouts occur when birds encounter weather fronts with strong headwinds near the end of their migration routes. Nearly emaciated, these birds no longer have the strength to fly through the fronts, and are forced to find terrestrial landing sites. Coastal thickets and oil platforms are usual recovery sites. The other type of migration is short distance migration. It is most often triggered by temperature changes and usually occurs when breeding habitat has become inhospitable due to lack of food availability. Bird species move only as far to find food resources. Attitudinal migration is a form of short distance migration. Attitudinal migrants move from higher elevations to lower ones during suboptimal conditions.

Breeding

Courtship

Breeding usually involve some type of courtship display, most often performed by the male.^[3] Most are rather simple, and usually involve some type of song. Some displays can be quite elaborate, using such varied methods as tail and wing drumming, dancing, aerial flights, and communal leks depending on the species. Females are most often involved with partner selection.^[4] Courtship feeding, billing and preening are commonly performed between partners, most often after birds have been paired and mated.^[5]

Social systems

The three mating systems that predominate among birds are monogamy (seen in approximately 91% of bird species), polygyny (2%) and polyandry (< 1%). Monogamous species of males and females pair for the breeding season. In some cases, the individuals may pair for life.

One reason for the high rate of monogamy among birds is the fact that male birds are just as adept at parental care as females. In most groups of animals, male parental care is rare, but in birds it is quite common; in fact, it is more extensive in birds than in any other vertebrate class. In birds, male care can be seen as important or essential to female fitness. "In one form of monogamy such as with obligate monogamy a female cannot rear a litter without the aid of a male".^[6]

The parental behavior most closely associated with monogamy is male incubation. Interestingly, male incubation is the most confining male parental behavior. It takes time and also may require physiological changes that interfere with continued mating. This extreme loss of mating opportunities leads to a reduction in reproductive success among incubating males. Gowaty (1983) notes that "This information then suggests that sexual selection may be less intense in taxa where males incubate, hypothetically because males allocate more effort to parental care and less to mating".^[7] In other words, in bird species in which male incubation is common, females tend to select mates on the basis of parental behaviors rather than physical appearance.

Territories and breeding sites

Many birds actively defend a territory from others of the same species during the breeding season. Large territories are protected in order to protect the food source for their chicks. Species that are unable to defend feeding territories, such as seabirds and swifts, often breed colonially instead, which is thought to offer protection from predators. Colonial breeders will defend small nesting sites, and competition between and withing species for nesting sites can be intense.

Eggs and nesting

All birds lay amniotic eggs^[8] with hard shells made mostly of calcium carbonate. Non-passerines typically have white eggs, except in some ground-nesting groups such as the Charadriiformes, sandgrouse and nightjars, where camouflage is necessary, and some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs, even if, like the tits they are hole-nesters.

The eggs are usually laid in a nest, with the exception of some cuckoos and cowbirds, which lay their eggs in other species nests. The host species then becomes responsible for raising the brood parasitic species young. Some nests can be extremely primitive, no more than a scrape on the ground. This is especially prevalent in ground nesting species where the newly hatched young are precocial. Most species build more elaborate nests, as more species raise altricial young. Some can be elaborately decorated structures such as those of the oropendolas.

Parental care and fledging

Parental care varies widely amongst different orders and species. At one extreme parental care in megapodes ends at hatching, with the chick being able to care for itself immediately. At the other extreme many seabirds have extended periods of parental care, the longest being Great Frigatebird, the chicks of which taking up to six months to fledge and being fed by the parents for up to 14 months after that.^[9]

In some species the care of young is shared between both parents, in other species it is the responsibility of just one sex. In some species other members of the same species will help the breeding pair in raising the young,. These helpers are usually the chicks of the breeding pair from previous breeding seasons.^[10] Alloparenting is particularly common in the corvids, but has been observed in as different species as the Rifleman, Red Kite and Australian Magpie.

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 calls out to sea, where they are raised away from terrestrial predators.^[11] Some other species, especially ducks, move their chicks away from the nest at an early age. In most species chicks leave the nest soon after, or just before, they are able to fly. Parental care after fledging varies; in albatrosses chicks leave the nest alone and recieve no further help, other species continue some supplementary feeding after fledging. Chicks may also follow their parents during their first migration.

Brood parasites

File:Reed warbler cuckoo pho.jpg

This Reed Warbler is rasing the young of a Common Cuckoo, a brood parasite.

Although some insects and fish engage in brood parasitism, the most brood parasites are birds. Brood parasites are birds which lay their eggs in the nests of other birds. These eggs are often accepted and raised by the host species, often at the cost of their own brood. There are two kinds of brood parasite, obligate brood parasites, which are incapable of raising their own young and must lay their eggs in the nests of other species; and non-obligate brood parasites, which are capable of rasining their own young but lay eggs in nests of conspecifics in order to increase its reproductive output. The most famous obligate brood parasites are the cuckoos, although in total 100 species of cuckoo, honeyguide, icterid, estrildid finch and duck are obligate parasites.^[12] Some brood parasites are adapted to hatching before their hosts and pushing their hosts eggs out of the nest, ensuring that all the food brought to the nest is fed to them.

Diet and Feeding

Birds feed on a variety of materials, including nectar, fruit, plants, seeds, carrion, and various types of small animals including other birds. Various feeding strategies are used by birds. Gleaning for insects, invertebrates, fruit and seeds is used by many species. Sallying from a branch and flycatching for insects is used by many songbirds. Drinking nectar is used primarily by hummingbirds and sunbirds. Probing for invertebrates is used by kiwis and shorebirds. Pursuit diving is used by falcons and accipiters in the air, and by loons, diving ducks and penguins in the water. Plunge diving is used by sulids, kingfishers and terns. Geese and dabbling ducks are primarily grazers. Some species will pirate, or steal food items from other birds. Frigatebirds, gulls, and skuas employ this type of feeding behavior. Finally, some birds are scavengers such as gulls and vultures. Some birds may employ many strategies to obtain food, while others are considered specialists.

Birds and humans

Birds are an important food source for humans. The most commonly eaten species is the domestic chicken and its eggs, although geese, pheasants, turkeys, and ducks are also widely eaten. Fowl grown for human consumption are referred to as poultry.

At one time swans and flamingos were delicacies of the rich and powerful, although these are generally protected now.

Besides meat and eggs, birds provide other items useful to humans, including feathers for bedding and decoration, guano-derived phosphorus and nitrogen used in fertilizer and gunpowder, and the central ingredient of bird's nest soup.

Other birds have long been used by humans to perform tasks. For example, homing pigeons were used to carry messages before the advent of modern instant communications methods (many are still kept for sport). Falcons are still used for hunting, while cormorants are employed by fishermen. Chickens and pigeons are popular as experimental subjects, and are often used in biology and comparative psychology research. As birds are very sensitive to toxins, the Canary was used in coal mines to indicate the presence of poisonous gases, allowing miners sufficient time to escape without injury.

Colorful, particularly tropical, birds (e.g. parrots, and mynas) are often kept as pets although this practice has led to the illegal trafficking of some endangered species; CITES, an international agreement adopted in 1963, has considerably reduced trafficking in the bird species it protects.

Bird diseases that can be contracted by humans include psittacosis, salmonellosis, campylobacteriosis, Newcastle's disease, mycobacteriosis (avian tuberculosis), avian influenza(bird flu), giardiasis, and cryptosporidiosis.

Many homeowners erect bird feeders near their homes to attract various species to their yards. Bird feeding has grown into a multimillion dollar industry.

Birds in popular culture

Birds feature prominently in folklore and popular culture. They generally tend to be portrayed as benign with hidden talents. Examples include Big Bird, Woodstock, Woody Woodpecker, and Donald and Daffy Duck. Sometimes, birds are associated with a darker side, as exemplified by Edgar Allen Poe's poem The Raven, the comic book series The Crow, or the appearance of various nocturnal owl species during frightening moments in television and movies. Most often eagles and hawks appear as regal characters, with the former often used as a national symbol for various countries. The cuckoo clock remains a popular timepiece. The clocks hourly signal is made to imitate the call of Europes Common Cuckoo. Various musical groups have been named after birds such as the Eagles, the Fabulous Thunderbirds and Flock of Seagulls. Feature length movies with birds as the predominant theme include Alfred Hitchcock's The Birds, The Birdman of Alcatraz, Winged Migration, March of the Penguins, and Happy Feet. Professional and school athletic teams have used birds as mascots. Birds have been referenced throughout literature, music and mythology. Many automobiles have been named after birds.

Distribution and conservation

Bird species breed on all 7 continents, with the highest diversity occurring in tropical regions. They are also found on all the worlds oceans.

Humans have had a large impact on many bird species. Human activities have in some cases allowed some species to dramatically expand their natural ranges, in other species ranges have decreased and have even resulted in many extinction. Over a hundred species have gone extinct in historical times, although the most dramatic extinctions occurred in the Pacific Ocean as humans colonised the ilsands of Melanesia, Polynesia and Micronesia, during which an estimated 750-1800 species of bird went extinct.^[13] According to Worldwatch Institute, many bird populations are currently declining worldwide, with 1,200 species facing extinction in the next century.^[14] The biggest cited reason surrounds habitat loss.^[15] Other threats include overhunting, accidental mortality due to structural collisions and as long-line fishing bycatch, pollution, competition and predation by nonnative invasive species,^[16] oil spills and pesticide use and climate change. Governments, along with numerous conservation charities, work to protect birds, either through laws to protect birds, preserving and restoring bird habitat or establishing captive populations for reintroductions.

Some species have come to depend on human activities for food and are widespread to the point of being pests. For example, the common pigeon or Rock Pigeon (Columba livia) thrives in urban areas around the world. Many bird species have been introduced to new locations by humans and have become established. This has either been done deliberately, for example Common Pheasants were widely introduced for sporting reasons; or acidentally, for example escaped pets such as Monk Parakeets establishing in a number of cities.

References

^ Template:Del Hoyo, Josep, et al. ''Handbook of Birds of the World Vol 1''. 1992. Barcelona: Lynx Edicions, ISBN 84-87334-10-5
^ "Early Adaptive Radiation of Birds: Evidence from Fossils from Northeastern China -- Hou et al. 274 (5290): 1164 -- Science". Retrieved 2006-07-21.
^ Short, Lester L., (1993) Birds of the World and their Behavior, Henry Holt and Co., ISBN 0-8050-1952-9
^ Burton, Robert, (1985) Bird Behavior, Alfred A. Knopf, Inc., ISBN 0-394-53857-5
^ Attenborough, David,(1998) The Life of Birds, Princeton University Press, ISBN 0-691-01633-X
^ Gowaty, Patricia Adair (1983). "Male Parental Care and Apparent Monogamy among Eastern Bluebirds (Sialia sialis)". The American Naturalist. 121 (2): 149–160. {{cite journal}}: Unknown parameter |quotes= ignored (help)
^ Ketterson, Ellen D. (1994). "Male Parental Behavior in Birds". Annual Review of Ecology and Systematics. 25: 601–28. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |quotes= ignored (help)
^ "Education - Senior 1". Manitoba Fisheries Sustainable Development. Retrieved 2006-10-09.
^ Metz, V.G. & Schreiber, E.A. (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
^ Ekman J. (2006) "Family living amongst birds" Journal of Avian Biology 37(4): 289-298
^ Gaston, A. J. (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.
^ Davies, N. (2000) Cuckoos, Cowbirds and other Cheats. T &A D Poyser:London ISBN 0-85661-135-2
^ Steadman D, (2006). Extinction and Biogeography in Tropical Pacific Birds, University of Chicago Press. ISBN 978-0-226-77142-7
^ "Worldwatch Paper #165: Winged Messengers: The Decline of Birds". Retrieved 2006-07-21. {{cite web}}: Text "Worldwatch Institute" ignored (help)
^ "Help Migratory Birds Reach Their Destinations". Retrieved 2006-07-21.
^ "Protect Backyard Birds and Wildlife: Keep Pet Cats Indoors". Retrieved 2006-07-21.

External links

Avibase - The World Bird Database
International Ornithological Committee
Birdlife International - Dedicated to bird conservation worldwide; has a database with about 250,000 records on endangered bird species
Birdingonthe.net
Worldtwitch - Rare bird news around the world
The Internet Bird Collection - A free library of videos of the world's birds
Birds Guide - Information and news about birds around the world
Bird Hybrids Database - Search by bird name, use Sibley
Bibliography on birds of Nicaragua - A free library of pdf

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[1] Template:Del Hoyo, Josep, et al. ''Handbook of Birds of the World Vol 1''. 1992. Barcelona: Lynx Edicions, ISBN 84-87334-10-5

[2] "Early Adaptive Radiation of Birds: Evidence from Fossils from Northeastern China -- Hou et al. 274 (5290): 1164 -- Science". Retrieved 2006-07-21.

[3] Short, Lester L., (1993) Birds of the World and their Behavior, Henry Holt and Co., ISBN 0-8050-1952-9

[4] Burton, Robert, (1985) Bird Behavior, Alfred A. Knopf, Inc., ISBN 0-394-53857-5

[5] Attenborough, David,(1998) The Life of Birds, Princeton University Press, ISBN 0-691-01633-X

[6] Gowaty, Patricia Adair (1983). "Male Parental Care and Apparent Monogamy among Eastern Bluebirds (Sialia sialis)". The American Naturalist. 121 (2): 149–160. {{cite journal}}: Unknown parameter |quotes= ignored (help)

[7] Ketterson, Ellen D. (1994). "Male Parental Behavior in Birds". Annual Review of Ecology and Systematics. 25: 601–28. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |quotes= ignored (help)

[8] "Education - Senior 1". Manitoba Fisheries Sustainable Development. Retrieved 2006-10-09.

[9] Metz, V.G. & Schreiber, E.A. (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

[10] Ekman J. (2006) "Family living amongst birds" Journal of Avian Biology 37(4): 289-298

[11] Gaston, A. J. (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.

[12] Davies, N. (2000) Cuckoos, Cowbirds and other Cheats. T &A D Poyser:London ISBN 0-85661-135-2

[13] Steadman D, (2006). Extinction and Biogeography in Tropical Pacific Birds, University of Chicago Press. ISBN 978-0-226-77142-7

[14] "Worldwatch Paper #165: Winged Messengers: The Decline of Birds". Retrieved 2006-07-21. {{cite web}}: Text "Worldwatch Institute" ignored (help)

[15] "Help Migratory Birds Reach Their Destinations". Retrieved 2006-07-21.

[16] "Protect Backyard Birds and Wildlife: Keep Pet Cats Indoors". Retrieved 2006-07-21.

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