Blue jay
| Blue jay | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Diademed Jay ( Cyanocitta stelleri ) |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Cyanocitta | ||||||||||||
| Strickland , 1845 |
The blue jays ( Cyanocitta ) are a genus of corvids (Corvidae). With the blue jay ( Cyanocitta cristata ) and the diademed jay ( Cyanocitta stelleri ), they include two small representatives of this family with blue plumage, black-banded large plumage and characteristic head of feathers. The distribution of the genus is limited to temperate North America, where the Rocky Mountains separate the two species. Blue jays inhabit deciduous, mixed and coniferous forests and feed mainly on plant seeds - especially acorns - invertebrates and small vertebrates. As omnivores , they also use many other food sources, including human food . Both species breed from spring to early summer. The crested jays build their nests in tree tops or bushes, their clutches usually contain three to six eggs. They are the only American corvid species to use mud when building their nests. Despite their close relatives and some similarities, they sometimes show strong differences in their way of life, for example with regard to migration behavior, sociality or when mating.
The genus Cyanocitta was first described by Hugh Edwin Strickland in 1845 . It belongs to the Neuwelthähern , a group in America endemic Raven bird species with blue plumage, and provides within this line of development one of the derived most genera represent. Are the next with the Schopfhähern used which also North American Scrub Jay ( Aphelocoma ) and the pinyon jay ( Gymnorhinus ). While it has long been assumed that the ancestors of the tiara and blue jay separated during the last ice ages , DNA studies suggest a separation around five million years ago.
features
Build and color
Both species of crested jay are relatively petite corvids with very similar build, but of different sizes. The blue jay is 30–34 cm in length or 100–142 g in body weight, larger and heavier than the 25–34 cm tall and 70–100 g heavy blue jay. There is little overlap in the dimensions of both species. The beak of the crested jay, with its strong shape, curved at the tip, corresponds to the basic building plan of the family. It is colored black and has a small strangler tooth at its end . The nasal bristles are very short and barely cover the nostrils of the beak. The slightly rounded tail is medium to elongated in relation to the rest of the body, while the wings are relatively short. When put on, their tips only reach just beyond the base of the tail. A diagnostic feature of the blue jays is their feather hood. It is less developed in the blue jay than in the diademed jay. Males become slightly larger than females in both species.
The blue, black and white tones of the crested jays' plumage correspond to the typical pattern of the New World jays . The two species show very different drawings: while the blue jay has a variable color with a black tail, blue rump plumage and black to blue head, the blue jay shows a fairly uniform pattern with a blue upper side, white lower side and black face mask. However, both types have black banded tail feathers , arm wings , umbrella feathers and wing covers ; a trait that all other New World crows lack and that is diagnostic of all American corvidae species. The beak and legs of both blue jays are black-gray. There is no difference in color between males and females, and young animals also differ only slightly from adults .
Flight image and locomotion
While the blue jay flies with powerful, deliberate flaps of its wings, the blue jay's cross-country flight is characterized by flat flaps of its wings. The latter overcomes shorter distances with a gradually sloping flight, in which phases of rapid wing beats alternate with gliding phases. On the ground, both species tend to hop rather than stride due to their small size and rather short legs. In the branches, blue jays move very agile from branch to branch.
Vocalizations
Blue jays have a very broad repertoire of calls. This includes croaking, energetic vocalizations as well as guttural or melodic calls such as subsongs . The vocabulary of both types is very different. They only show certain similarities, for example in the taste of female birds. Blue jays and blue jays are considered good imitators and often utter calls that are very similar to those of other birds and mammals. Both species are known to imitate the calls of buzzards ( Buteo spp.) And other birds of prey . The sounds of mammals or mechanical ambient noises are also imitated by blue teasers and tiara. How strongly this behavior in nature is based on conscious, active imitation and what purpose it serves is controversial.
Spreading and migrations
The blue jays are common throughout temperate North America and are separated from each other by the North American Cordilleras . The current distribution pattern is likely a result of the glaciation of large parts of North America during the last glacial period . While the blue jay occurs in the rather flat eastern part of the continent up to the Rocky Mountains , the diademed jay lives parapatric to it in the western mountains and the adjacent temperate and mountainous regions. Blue and tiara jays are only found regionally sympatric in southwest Canada . Both species advance to the northern border of the warm temperate zone in Canada and Alaska . They are missing in the arid deserts, valleys and coastal regions of the western continent. The distribution area becomes more fragmented towards the south. Only the diademed jay ventures into the tropics , but also only inhabits the cooler mountain regions there. Its southern limit of distribution is the lowlands of Nicaragua . In the Pleistocene it was probably isolated in various, ice-free heat islands in the south and west and penetrated into the Rocky Mountains after the glaciers had melted.
Clear differences between the two species of the genus can be seen in the migration behavior. While the blue jay, which is adapted to colder altitudes, is considered a resident bird and only leaves the highest altitudes in winter, the blue jay is the only species among the New World jays that also undertakes broad-based migrations throughout the year . Although some blue jays always stay in the summer breeding areas in winter, a large part of the population moves south, at least in the more northern parts of the range. In more southern latitudes - for example in Florida - the entire breeding population consists of resident birds. While the bird migration of the blue jay is largely constant in terms of time and geography, the blue jay can experience irruptive migratory movements after the end of the breeding season if there is a food shortage due to the increase in population. Many annual birds then leave the breeding areas and migrate to regions outside of it.
habitat
Crested jays are forest dwellers, but like most corvids avoid dense and closed forests. Instead, they are mainly found in gappy forms of vegetation , along the edges of forests, in parkland or urban green spaces. Both species show a great affinity for oak ( Quercus spp.), Where present, but do not necessarily depend on them. Typical habitats of the genus are coniferous and mixed forests , the blue jay also lives in pure deciduous forests . Both species can also be found in anthropogenic habitats, but use them differently. While the blue jay can often be found in cities and has a higher population density there than in forests, it is the other way around with the blue jay. Its settlement density drops significantly in areas of land interspersed with villages or towns, even compared to national parks, for example . While the occurrence of the diademed mower is concentrated at altitudes of 1000 to 3500 m, the blue jay shows no such attachment and occurs continuously from sea beaches to the Appalachian Mountains .
Way of life
nutrition
Blue jays are omnivores , but mainly feed on plant-based food. For both species, studies have shown a distribution of 75–80% plant material and 25–20% animal material in the diet. Acorns are an important food for the blue jays in large parts of their range and, where available, often make up the majority of the vegetable diet. But they can also be replaced with hazelnuts , pine seeds , beechnuts or similar nut fruits . The blue jay tends to use seeds from deciduous trees, while the blue jay tends to use conifer seeds due to its montane habitat . Where there are other sources of food, they are often exploited. Arthropods , small songbirds and mammals, as well as eggs, are not spurned.
Like all New World jays, the crested jays have a modified jaw joint. They belong to the genera in which this characteristic is particularly pronounced. It allows them to hammer pieces of food with their beak open and remove their shell at the same time. Laboratory studies with blue jays indicate that when searching for food, blue jays work with search images in which certain structures that indicate food objects stand out more clearly. The hiding instinct typical of Corvids is very pronounced in the European jays. Excess food is placed in crevices and holes in trees or first hammered into the ground with a beak and then covered over the hole.
Social and territorial behavior
The territorial behavior of blue jays is weak to moderate when compared to families. The blue jay defends a small area around the nest, the blue jay only the nesting site itself. The dominance of its own nesting site is demonstrated primarily by postures and figures. In both species, the breeding pair is the usual social unit in which birds roam. Both blue and tiara jays can come together in larger schools. While a certain cohesion can be seen in swarms of blue jays, larger blue jay groups tend to form spontaneously and randomly and have no momentum of their own. The individual distance between some birds is usually a few meters, but can be reduced to a few centimeters between individuals with a low status (such as this year's birds) or breeding partners.
Reproduction and breeding
As is usual with corvids, crested jays usually form lifelong, monogamous breeding pairs. Separations only occur in rare cases. The courtship behavior is different in both species; While the male initiates mating with the blue jay, it is done by the female with the blue jay. Blue jays build their nests in the treetops or the branches of bushes. The height of the nest varies and can be 1–30 m. The blue jay usually builds at a height of 3–5 m, with the blue jay there is no clear preference. Both sexes participate in nest building, but the actual construction is primarily done by the female. The outside of the nest consists of a shell made of thick, coarsely layered twigs that are woven with softer materials such as leaves, hair, feathers or even paper. On the inside, blue jays apply mud, which is then lined with soft, fine roots. They are the only genus of New World Jay that uses mud to build nests.
The eggs are darkly speckled on a light background and are probably laid every day. It takes around two and a half weeks for the young to hatch and roughly the same time for the young to fled. The female incubates the eggs alone and is fed by the male during this time. Even after the trip out of the nest, the young are still fed by their parents.
Systematics
Taxonomy and research history
The crested jay genus was first described by Hugh Edwin Strickland in 1845 . He separated them from the blue ravens ( Cyanocorax ) in order to take their different morphology and way of life into account. The crested jays, according to Strickland, differ from the blue ravens to the same extent as the genus Garrulus from the ravens and crows ( Corvus ). As a type kind he chose the Blue Jays ( Cyanocitta cristata ). The generic name Cyanocitta is derived from the Greek terms κύανος kyanos for blue and κίττα kitta , a name for the magpie . Strickland also placed those species in the genus that are today attributed to the bush jays ( Aphelocoma ). At times also were beside the Buschhähern cyanolyca ( Cyanolyca ) and the " Cissilopha " -Blauraben considered CYANOCITTA, at the latest John William Hardys revision of 1969 but included the genus only the blue and the Steller. The blue jay was known to European naturalists as early as the 16th century and was first described by Carl von Linné in 1758 . The diademed jay was discovered by Georg Wilhelm Steller during the Second Kamchatka Expedition in 1741 and described by Johann Friedrich Gmelin in 1789 .
External system
|
|||||||||||||||||||||||||||
| Internal systematics of the recent New World jays according to Bonaccorso & Peterson 2007. The closest related genus of the crested jays are the North American bush jays . |
The relationship between the blue jays and other New World hay species has long been considered unclear. Hardy was unable to identify any closer relationship to any of the other groups on the basis of ecology and morphology, Derek Goodwin suspected in 1986 a closer relationship to the Bushmen. In fact, analyzes of various gene sequences by Elisa Bonaccorso and A. Townsend Peterson classified the common jays and the crested jays as sister taxa in 2007 . Together they face the naked jay ( Gymnorhinus cyanocephalus ) as a sister clade. The bootstrap support for this arrangement is low; Another arrangement of the three genera among one another would also be conceivable on the basis of the analyzed sequences. In contrast to all other New World jays, however, the bush and crested jays show a lateral marginal bone on the scleral ring , which suggests a close relationship. The clade formed by the bald-beaked, bush and crested jays probably developed against the late Miocene or early Pliocene in southern North America and settled in the north of the continent in the period that followed. Despite the relatively large distance to other genera, the blue jay hybridizes with some bush jays and blue ravens.
Internal system
Because tiara and blue jays inhabit the west and east of North America, respectively, it has long been assumed that the cold periods of the Pleistocene and the glaciation of the Rocky Mountains were the decisive events for speciation . Because the two species hybridize with each other, a late separation around 100,000 years ago was considered likely. Relatively large differences in the cytochrome b sequences of 10.7–24.8%, however, indicate an earlier separation. In the molecular clock scheme , the ancestors of the two species should have separated around 5 million years ago, i.e. at the beginning of the Pliocene .
swell
literature
- Brian S. Arbogast, Joseph B. Slowinski: Pleistocene Speciation and the Mitochondrial DNA Clock. In: Science 282, 1998. S. 1995a.
- Elisa Bonaccorso, Andrew Townsend Peterson: A Multilocus Phylogeny of New World Jay Genera. In: Molecular Phylogenetics and Evolution 42, 2007. doi : 10.1016 / j.ympev.2006.06.025 , pp. 467-476.
- Theresa M. Burg, Anthony J. Gaston, Kevin Winker, Vicky L. Friesen: Rapid Divergence and Postglacial Colonization in Western North American Steller's Jays (Cyanocitta stelleri). In: Molecular Ecology 14, 2005. doi : 10.1111 / j.1365-294x.2005.02710.x , pp. 3745-3755.
- Johann Friedrich Gmelin: Caroli a Linné systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis… Editio decima tertia, aucta, reformata. Regnum Animale. Georg Emanuel Beer, Leipzig 1788. doi : 10.5962 / bhl.title.545
- Derek Goodwin: Crows of the World. 2nd Edition. The British Museum (Natural History) , London 1986. ISBN 0565009796 .
- John William Hardy: A Taxonomic Revision of the New World Jays. In: The Condor 71, 1969. pp. 360-375. ( Full text ; PDF; 1.5 MB)
- Joseph del Hoyo, Andrew Elliot, David Christie (Eds.): Handbook of the Birds of the World. Volume 14: Bush-shrikes To Old World Sparrows. Lynx Edicions, Barcelona 2009. ISBN 9788496553507 .
- Carl von Linné: Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Lars Salvi, Stockholm 1758. ( full text )
- Steve Madge , Hilary Burn: Crows & Jays. Princeton University Press, Princeton 1994, ISBN 0-691-08883-7 .
- Hugh Edwin Strickland: On Cyanocitta, a Proposed New Genus of Garrulinae, and on C. superciliosa, a New Species of Blue Jay, hitherho Confounded with C. ultramarina, Bonap .. In: The Annals and Magazine of Natural History, Including Zoology, Botany and Geology 15 (98), 1845. pp. 260-261. ( Full text )
- Richard L. Zusi: A Feeding Adaption of the Jaw Articulation in the New World Jays (Corvidae). In: The Auk 104, 1987. pp. 665-680.
Web links
- Erick Greene, William Davison, Vincent R. Muehter: Steller's Jay (Cyanocitta stelleri). In: A. Poole: The Birds of North America Online (343), Cornell Lab of Ornithology, Ithaca 1998. doi : 10.2173 / bna.343 .
- Keith A. Tarvin, Glen E. Woolfenden : Blue Jay (Cyanocitta cristata). In: A. Poole: The Birds of North America Online (469), Cornell Lab of Ornithology, Ithaca 1999. doi : 10.2173 / bna.469 .
Individual evidence
- ↑ Strickland 1845 , p. 261.
- ↑ a b c d e f g h i j k Tarvin & Woolfenden 1999 . Retrieved April 3, 1999.
- ↑ a b c d e f g h i j k l m n Greene et al. 1998 . Retrieved April 3, 2012.
- ↑ Madge & Burn 1994 , pp. 67-70.
- ↑ Burg et al. 2005 , p. 3752.
- ↑ Goodwin 1986 , p. 227.
- ↑ del Hoyo 2009 , p. 569.
- ↑ Goodwin 1986 , p. 228.
- ↑ Zusi 1987 , pp. 669-671.
- ↑ Goodwin 1986 , pp. 227-233.
- ↑ Strickland 1845 , pp. 260-261.
- ↑ Amadon 1944 , p. 6.
- ↑ Hardy 1969 , pp. 370-371.
- ↑ by Linné 1758 , p. 106.
- ↑ Gmelin 1788 , p. 370.
- ↑ Hardy 1969 , p. 370.
- ↑ Goodwin 1986 , p. 222.
- ↑ Bonaccorso & Peterson 2007 , pp. 472-474.
- ↑ del Hoyo 2009 , p. 568.
- ↑ Arbogast & Slowinski 1998 , p. 1995a.
Footnotes directly after a statement confirm this individual statement, footnotes directly after a punctuation mark the entire preceding sentence. Footnotes after a space refer to the entire preceding text.
