Western jackdaw
Western jackdaw | |
---|---|
Coloeus monedula | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Passeriformes |
Family: | Corvidae |
Genus: | Coloeus |
Species: | C. monedula
|
Binomial name | |
Coloeus monedula | |
Jackdaw range
summer-only range
winter visitor only
| |
Synonyms | |
The western jackdaw (Coloeus monedula), also known as the Eurasian jackdaw, the European jackdaw, or simply the jackdaw, is a
Measuring 34–39 centimetres (13–15 in) in length, the western jackdaw is a black-plumaged bird with a grey
Systematics
Etymology
The western jackdaw was one of the many species originally described by
The original
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.[10] Formerly, western jackdaws were simply called "daws".[7] The metallic chyak call may be the origin of the jack part of the common name,[11] but this is not supported by the Oxford English Dictionary.[12] 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.
Names in English dialects are numerous. Scottish and north English dialects have included ka or kae since the 14th century. The
An archaic collective noun for a group of jackdaws is a "clattering".[17] Another name for a flock is a "train".[18]
Taxonomy
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.
Subspecies
There are four recognized subspecies of the western jackdaw.
- The Nordic jackdaw (C. m. monedula) (Linnaeus, 1758), the nominate subspecies, is found in eastern Europe. Its range extends across Scandinavia, from southern Finland south to Esbjerg and Haderslev in Denmark, through eastern Germany and Poland, and south across eastern central Europe to the Carpathian Mountains and northwestern Romania, Vojvodina in northern Serbia, and Slovenia.[28] It breeds in south-eastern Norway, southern Sweden, and northern and eastern Denmark, with occasional wintering in England and France. It has been recorded as a rare vagrant to Spain.[29] It has a pale nape and sides of the neck, a dark throat, and a light grey partial collar of variable extent.[26]
- The Western Eurasian jackdaw (C. m. spermologus) (Vieillot, 1817) occurs in western, central and southern Europe and North Africa, from the British Isles, the Netherlands and the Rhineland in the north, through western Switzerland into Italy in the southeast, and the Iberian peninsula and Morocco in the south.[28] It winters in the Canary Islands and Corsica. The name "spermologus" comes from the Greek σπερμολόγος, a picker of seeds.[30] It is darker in colour than the other subspecies and lacks the whitish border at the base of the grey nape.[26]
- The Eastern Eurasian jackdaw (C. m. soemmerringii) (Johann Fischer von Waldheim described this taxon as Corvus soemmerringii in 1811, noting its differences from populations in western Europe.[31] Its subspecific name was given in honour of the German anatomist Samuel Thomas von Sömmerring. It is distinguished by the nape and the sides of the neck being paler, creating a contrasting black crown and lighter grey part collar.[26]
- The Algerian jackdaw (C. m. cirtensis) (Rothschild and Hartert, 1912) is found in Morocco and Algeria in Northwest Africa. It was also formerly found in Tunisia.[28] The name "cirtensis" refers to the ancient city of Cirta in Numidia. The plumage is duller and more uniformly dark grey than the other subspecies, with the paler nape less distinct.[26]
Description
The western jackdaw measures 34–39 centimetres (13–15 in) in length and weighs around 240 grams (8.5 oz).[32][33] 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,[34] 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,[32] the length of which is about 75% of the length of the rest of the head.[34] There are rictal bristles covering around 40% of the maxilla and 25% of the lower mandible.[34] 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.[32] The sexes look alike,[13][35] though the head and neck plumage of male birds fades more with age and wear, particularly just before moulting.[36] Western jackdaws undergo a complete moult from June to September in the western parts of their range, and a month later in the east.[28] The purplish sheen of the cap is most prominent just after moulting.[36]
Immature birds have duller and less demarcated plumage.[37] 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.[36]
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.[34]
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.[37] 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.[38] 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.[37]
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.[37] 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.[39] 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.[40]
Vocalisations
Western jackdaws are voluble birds. The main call, frequently given in flight, is a metallic and squeaky chyak-chyak or kak-kak.
Distribution and 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.[26] However, it is regionally extinct in Malta and Tunisia.[1] 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.[45] 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.[46] The UK population was estimated at 2.5 million individuals in 1998, up from 780,000 in 1970.[47]
Most populations are resident, but the northern and eastern populations are more migratory,
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.[26] 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).[37] 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.[53] 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.[54]
Behaviour
Generally wary of people in the forest or countryside, western jackdaws are much tamer in urban areas.[55]
Highly gregarious, western jackdaws are generally seen in flocks of varying sizes, though males and females pair-bond for life and pairs stay together within flocks.[56] Flocks increase in size in autumn and birds congregate at dusk for communal roosting,[13] with up to several thousand individuals gathering at one site. At Uppsala, Sweden, 40,000 birds have been recorded at a single winter roost with mated pairs often settling together for the night.[55] Western jackdaws frequently congregate with hooded crows[35] or rooks,[37] the latter particularly when migrating or roosting.[57] They have been recorded foraging with the common starling (Sturnus vulgaris), Northern lapwing (Vanellus vanellus), and common gull (Larus canus) in northwestern England.[57] Flocks are targets of coordinated hunting by pairs of lanner falcons (Falco biarmicus), although larger groups are more able to elude the predators.[58] Western jackdaws sometimes mob and drive off larger birds such as European magpies, common ravens, or Egyptian vultures (Neophron percnopterus); one gives an alarm call which alerts its conspecifics to gather and attack as a group.[43] Occasionally, a sick or injured western jackdaw is mobbed until it is killed.[59]
In his book
Social displays
Social hierarchy in western jackdaw flocks is determined by supplanting, fighting, and
Western jackdaws entreat their partners to preen them by showing their nape and ruffling their head feathers. Birds mainly preen each other's head and neck. Known as allopreening, this behaviour is almost always done between birds of a mated pair.[62]
Breeding
Western jackdaws become sexually mature in their second year. Genetic analysis of pairs and offspring shows no evidence of extra-pair copulation[56] and there is little evidence for couple separation even after multiple instances of reproductive failure.[63] Some pairs do separate in the first few months, but almost all pairings of over six months' duration are lifelong, ending only when a partner dies.[57] Widowed or separated birds fare badly, often being ousted from nests or territories and unable to rear broods alone.[57]
Western jackdaws usually breed in colonies with pairs collaborating to find a nest site, which they then defend from other pairs and predators during most of the year.[63] They nest in cavities in trees or cliffs, in ruined or occupied buildings and in chimneys, the common feature being a sheltered site for the nest. The availability of suitable sites influences their presence in a locale.[37] They may also use church steeples for nesting, a fact reported in verse by 18th century English poet William Cowper:
A great frequenter of the church,
Where, bishoplike, he finds a perch,
And dormitory too.[64]
Nest platforms can attain a great size. A mated pair usually constructs a nest by improving a crevice by dropping sticks into it; it is then built on top of the platform formed.[59] This behaviour has led to the blocking of chimneys and even resulted in nests crashing down into fireplaces, sometimes with birds still on them.[65]
In his The Natural History of Selborne, Gilbert White notes that western jackdaws used to nest in crevices beneath the lintels of Stonehenge, and describes an example of the bird using a rabbit burrow for nesting.[18] The species has been recorded outcompeting the tawny owl (Strix aluco) for nest sites in the Netherlands.[66] They can take over old nest sites of the black woodpecker (Dryocopus martius)[67] and stock dove (Columba oenas).[62] Breeding colonies may also edge out those of the red-billed chough, but in turn be ousted by larger corvids such as the carrion crow, rook or magpie.[62]
Nests are lined with hair, wool, dead grass and many other materials.
Western jackdaws hatch asynchronously and incubation begins before clutch completion, which often leads to the death of the last-hatched young. If the supply of food is low, parental investment in the brood is kept to a minimum as little energy is wasted on feeding a chick that is unlikely to survive.[72] Replacement clutches are very rarely laid in the event of clutch failure.[70]
The
Feeding
Foraging takes place mostly on the ground in open areas and to some extent in trees.[26] Landfill sites, bins, streets, and gardens are also visited, more often early in the morning when there are fewer people about.[26] Various feeding methods are employed, such as jumping, pecking, clod-turning and scattering, probing the soil, and occasionally, digging. Flies around cow pats are caught by jumping from the ground or at times by dropping vertically from a few metres onto the cow pat. Earthworms are not usually extracted from the ground by western jackdaws but are eaten from freshly ploughed soil.[76] Jackdaws will ride on the backs of sheep and other mammals, seeking ticks as well as actively gathering wool or hair for nests, and will catch flying ants in flight.[40] Compared with other corvids, the western jackdaw spends more time exploring and turning over objects with its bill; it also has a straighter and less downturned bill and increased binocular vision which are advantageous for this foraging strategy.[77]
The western jackdaw tends to feed on small
Opportunistic and highly adaptable, the western jackdaw varies its diet markedly depending on available food sources.
Western jackdaws practice active food sharing – where the initiative for the transfer lies with the donor – with a number of individuals, regardless of sex or kinship. They also share more of a preferred food than a less preferred food.
Parasites and diseases
Western jackdaws have learned to peck open the foil caps of milk bottles left on the doorsteps after delivery by the milkman. The bacterium
An outbreak of a gastrointestinal illness in Spain which was causing mortalities in humans has been linked to western jackdaws. During a post-mortem on an affected bird, a polyomavirus was isolated from the spleen. The illness appeared to be a co-infection of this with Salmonella and the virus has been provisionally named the crow polyomavirus (CPyV).[91] Segmented filamentous bacteria have been isolated from the small intestine of a western jackdaw, although their pathogenicity or role is unknown.[92]
Pest control
The western jackdaw has been hunted as vermin, though not as heavily culled as other species of corvid.
The western jackdaw is one of a very small number of birds that it is legal to use as a decoy or to trap in a cage in the United Kingdom. The other pest species that can be controlled by trapping are the crow, jay, magpie and rook. An authorised person must comply with the requirements of the Wildlife and Countryside Act 1981 and does not need to show that the birds were a nuisance before trapping them.[96] As of 2003 the western jackdaw was listed as a potential species for targeted hunting in the European Union Birds Directive, and hunting has been encouraged by German hunting associations.[95] Permission to shoot western jackdaws in spring and summer exists in Cyprus as they are thought (incorrectly) to prey on gamebirds.[80]
Cultural depictions and folklore
An ancient Greek and Roman adage runs "The swans will sing when the jackdaws are silent", meaning that educated or wise people will speak only after the foolish have become quiet.
In some cultures, a jackdaw on the roof is said to predict a new arrival; alternatively, a jackdaw settling on the roof of a house or flying down a chimney is an omen of death, and coming across one is considered a bad omen.
The jackdaw was considered sacred in Welsh folklore as it nested in church steeples – it was shunned by the Devil because of its choice of residence.[103] Nineteenth century belief in the Fens held that seeing a jackdaw on the way to a wedding was a good omen for a bride.[104]
The jackdaw is featured on the Ukrainian town of Halych's ancient coat of arms, the town's name allegedly being derived from the East Slavic word for the bird.[105] In The Book of Laughter and Forgetting (1979), Milan Kundera notes that Franz Kafka's father Hermann had a sign in front of his shop with a jackdaw painted next to his name, since "kavka" means jackdaw in Czech.[106]
In the video game Assassin's Creed IV: Black Flag, the main character's ship is named the Jackdaw.[citation needed]
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Coat of arms of the Principality of Halych
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Coat of arms of Halych Land
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Flag of Halych land at the Battle of Grunwald 1410
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Coat of arms of Ivano-Frankivsk Oblast
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{{cite book}}
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Works cited
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