Taccola

Identificazione

The western jackdaw measures 34–39 centimetres (13–15 in) in length and weighs around 240 grams (8.5 oz). Most of the plumage is a shiny black, with a purple (in subspecies monedula and spermologus) or blue (in subspecies cirtensis and soemmerringii) sheen on the crown, forehead, and secondaries, and a green-blue sheen on the throat, primaries, and tail. The cheeks, nape and neck are light grey to greyish-silver, and the underparts are slate-grey. The legs are black, as is the short stout bill, the length of which is about 75% of the length of the rest of the head. There are rictal bristles covering around 40% of the maxilla and 25% of the lower mandible. The irises of adults are greyish or silvery white while those of juveniles are light blue, becoming brownish before whitening at around one year of age. The sexes look alike, though the head and neck plumage of male birds fades more with age and wear, particularly just before moulting. Western jackdaws undergo a complete moult from June to September in the western parts of their range, and a month later in the east. The purplish sheen of the cap is most prominent just after moulting.<p>Immature birds have duller and less demarcated plumage. The head is a sooty black, sometimes with a faint greenish sheen and brown feather bases visible; the back and side of the neck are dark grey and the underparts greyish or sooty black. The tail has narrower feathers and a greenish sheen.<p>There is very little geographic variation in size. The main differences are the presence or absence of a whitish partial collar at the base of the nape, the variations in the shade of the nape and the tone of the underparts. Populations in central Asia have slightly larger wings and western populations have a slightly heavier bill. Body colour becomes darker further north, in mountain regions and humid climates, and paler elsewhere. However, individual variation, particularly in juveniles and also during the months before moulting, can often be greater than geographic differences.<p>A skilled flyer, the western jackdaw can manoeuvre tightly as well as tumble and glide. It has characteristic jerky wing beats when flying, though these are not evident when birds are migrating. Wind tunnel experiments show that the preferred gliding speed is between 6 and 11 metres (20 and 36 ft) per second and that the wingspan decreases as the bird flies faster. On the ground, western jackdaws have an upright posture and strut briskly, their short legs giving them a rapid gait. They feed with their heads held down or horizontally.<p>Within its range, the western jackdaw is unmistakable; its short bill and grey nape are distinguishing features. From a distance, it can be confused with a rook (Corvus frugilegus), or when in flight, with a pigeon or chough. Flying western jackdaws are distinguishable from other corvids by their smaller size, faster and deeper wingbeats and proportionately narrower and less fingered wing tips. They also have shorter, thicker necks, much shorter bills and frequently fly in tighter flocks. They can be distinguished from choughs by their uniformly grey underwings and their black beaks and legs. The western jackdaw is very similar in morphology, behaviour, and calls to the Daurian jackdaw, with which its range overlaps in western Asia. Adults are readily distinguished, since the Daurian has a pied plumage, but immature birds are much more similar, both species having dark plumage and dark eyes. The Daurian tends to be darker, with a less contrasting nape than the Western.<p>Western jackdaws are voluble birds. The main call, frequently given in flight, is a metallic and squeaky chyak-chyak or kak-kak. This is a contact or greeting call. A feeding call made by adults to call young, or males when offering food to their mates, has been transcribed as kiaw or kyow. Females in return give a more drawn out version when begging for food from males, written as kyaay, tchaayk or giaaaa. Perched birds often chatter together, and before settling for the night, large roosting flocks make a cackling noise. Western jackdaws also have a hoarse, drawn-out alarm call, arrrrr or kaaaarr, used when warning of predators or when mobbing them. Nestlings begin making a soft cheep at about a week of age. As they grow, their voice becomes louder until their call is a penetrating screech around day 18. After this, the voice deepens and softens. From day 25, the young cease calling and become silent if they hear an unfamiliar noise. The European jackdaw can be trained to imitate human speech.

Tassonomia

The western jackdaw was one of the many species originally described by Carl Linnaeus in his 18th century work Systema Naturae. Owing to its supposed fondness for picking up coins, Linnaeus gave it the binomial name Corvus monedula, choosing the specific name mǒnēdŭla, which is derived from moneta, the Latin stem of the word "money". Jackdaws are sometimes placed in the genus Coloeus, from the Ancient Greek κολοιός (koloios) for jackdaw, though most subsequent works have retained the two jackdaw species in Corvus.<p>The original Old English words ċēo and ċeahhe (pronounced with initial ch) gave modern English "chough"; Chaucer sometimes used this word to refer to the western jackdaw, as did Shakespeare in Hamlet although there has been debate about which species he was referring to. This onomatopoeic name, based on the western jackdaw's call, now refers to corvids of the genus Pyrrhocorax; the red-billed chough (Pyrrhocorax pyrrhocorax), formerly particularly common in Cornwall, became known initially as the "Cornish chough" and then just the "chough", the name transferring from one species to the other.<p>The common name jackdaw first appeared in the 16th century, and is thought to be a compound of the forename Jack, used in animal names to signify a small form (e.g. jack snipe), and the archaic native English word daw. Formerly, western jackdaws were simply called "daws". The metallic chyak call may be the origin of the jack part of the common name, but this is not supported by the Oxford English Dictionary. Daw, first used for the bird in the 15th century, is held by the Oxford English Dictionary to be derived from the postulated Old English dawe, citing the cognates in Old High German tāha, Middle High German tāhe or tāchele, and modern German Dahle or Dohle, and dialectal Tach, Dähi, Däche and Dacha.<p>Names in English dialects are numerous. Scottish and north English dialects have included ka or kae since the 14th century. The Midlands form of this word was co or coo. Caddow is potentially a compound of ka and dow, a variant of daw. Other dialectal or obsolete names include caddesse, cawdaw, caddy, chauk, college-bird, jackerdaw, jacko, ka-wattie, chimney-sweep bird (from their nesting propensities), and sea-crow (from the frequency with which they are found on coasts). It was also frequently known quasi-nominally as Jack.<p>An archaic collective noun for a group of jackdaws is a "clattering". Another name for a flock is a "train".<p>A study in 2000 found that the genetic distance between western jackdaws and the other members of Corvus was greater than that within the rest of the genus. This led Pamela Rasmussen to reinstate the genus name Coloeus, created by Johann Kaup in 1829, in her Birds of South Asia (2005), a treatment also used in a 1982 systematic list in German by Hans Edmund Wolters. A study of corvid phylogeny undertaken in 2007 compared DNA sequences in the mitochondrial control region of several corvids. It found that the western jackdaw, and the closely related Daurian jackdaw (C. dauuricus) of eastern Russia and China, were basal to the core Corvus clade. The names Coloeus monedula and Coloeus dauuricus have since been adopted by the International Ornithological Congress in their official list. The two species of jackdaw have been reported to hybridise in the Altai Mountains, southern Siberia, and Mongolia. Analysis of the mitochondrial DNA of specimens of the two species from their core ranges show them to be genetically distinct.<p>There are four recognized subspecies of the western jackdaw. All European subspecies intergrade where their populations meet. C. m. monedula intergrades into C. m. soemmerringii in a transition zone running from Finland south across the Baltic and eastern Poland to Romania and Croatia.

Nome scientifico

Coloeus monedula

Autorità

(Linnaeus, 1758)

Ordine

Passeriformi

Famiglia

Corvidi

Genere

Coloeus

Areale e habitat

The western jackdaw is found from Northwest Africa through all of Europe, except for the subarctic north, and eastwards through central Asia to the eastern Himalayas and Lake Baikal. To the east, it occurs throughout Turkey, the Caucasus, Iran, Iraq, Afghanistan, Pakistan, and northwestern India. However, it is regionally extinct in Malta and Tunisia. The range is vast, with an estimated global extent between 1 and 10 million square kilometres (0.4–4 million square miles). It has a large global population, with an estimated 15.6 to 45 million individuals in Europe alone. Censuses of bird populations in marginal uplands in Great Britain show that western jackdaws greatly increased in numbers between the 1970s and 2010, although this increase may be related to recovery from previous periods when they were regarded as pests. The UK population was estimated at 2.5 million individuals in 1998, up from 780,000 in 1970.<p>Most populations are resident, but the northern and eastern populations are more migratory, relocating to wintering areas between September and November and returning between February and early May. Their range expands northwards into Russia to Siberia during summer and retracts in winter. They are vagrants to the Faroe Islands, particularly in the winter and spring, and occasionally to Iceland. Elsewhere, western jackdaws congregate over winter in the Ural Valley in northwestern Kazakhstan, the northern Caspian, and the Tian Shan region of western China. They are winter visitors to the Quetta Valley in western Pakistan, and are winter vagrants to Lebanon, where they were first recorded in 1962. In Syria, they are winter vagrants and rare residents with some confirmed breeding taking place. The subspecies soemmerringii occurs in south-central Siberia and extreme northwestern China and is accidental to Hokkaido, Japan. A small number of western jackdaws reached northeastern North America in the 1980s and have been found from Atlantic Canada to Pennsylvania. They have also occurred as vagrants in Gibraltar, Mauritania, and Saint Pierre and Miquelon, and one is reported to have been seen in Egypt.<p>Western jackdaws inhabit wooded steppes, pastures, cultivated land, coastal cliffs, and towns. They thrive when forested areas are cleared and converted to fields and open areas. Habitats with a mix of large trees, buildings, and open ground are preferred; open fields are left to the rook, and more wooded areas to the Eurasian jay (Garrulus glandarius). Along with other corvids such as the rook, common raven (Corvus corax), and hooded crow (C. cornix), some western jackdaws spend the winter in urban parks; populations measured in three urban parks in Warsaw show increases from October to December, possibly due to western jackdaws migrating there from areas further north. The same data from Warsaw, collected from 1977 to 2003, showed that the wintering western jackdaw population had increased four-fold. The cause of the increase is unknown, but a reduction in the number of rooks may have benefited the species locally, or rooks overwintering in Belarus may have caused western jackdaws to relocate to Warsaw.

Migrazione

Migratori completi

Comportamento

Comportamento migratorio: Migratori completi.

Conservazione

Tendenza della popolazione: stabile.

Tendenza della popolazione

stabile