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- For the butterfly, see Chliaria kina.
Parus caeruleus Linnaeus, 1758
The Blue Tit (Cyanistes caeruleus or Parus caeruleus) is a small passerine bird in the tit family Paridae. The bird is easily recognisable by its blue and yellow plumage, but various authorities dispute their scientific classification.
Blue tits, usually resident and non-migratory birds, are widespread and a common resident breeder throughout temperate and subarctic Europe and western Asia in deciduous or mixed woodlands with a high proportion of oak. They usually nest in tree holes, although they easily adapt to nest boxes where necessary. The main rival for nests and search for food is the much larger Great Tit.
The blue tit prefers insects and spiders for their diet. Outside the breeding season, they also eat seeds and other vegetable-based foods. Blue tits are famed for their skill, as they can cling to the outermost branches and hang upside down when looking for food.
Most authorities retain Cyanistes as a subgenus of Parus, but the British Ornithologists' Union treats Cyanistes as a distinct genus. This is supported by mtDNA cytochrome b sequence analysis which suggests that Cyanistes is not only distinct, but not close to other tits.
The systematics of the Blue Tit complex are disputed. There are currently at least nine recognised subspecies:
- C. c. caeruleus (Linnaeus, 1758), the nominate subspecies, occurring in Continental Europe to northern Spain, Sicily, northern Turkey and northern Urals
- C. c. obscurus (Pražák, 1894), Ireland, Britain and Channel Islands
- C. c. ogilastrae (Hartert, 1905), Portugal, southern Spain, Corsica and Sardinia
- C. c. balearicus (von Jordans, 1913), Majorca Island (Balearic Islands)
- C. c. calamensis (Parrot, 1908), southern Greece, Pelopónnisos, Cyclades, Crete and Rhodes
- C. c. orientalis (Zarudny & Loudon, 1905), southern European Russia (Volga River to central and southern Urals)
- C. c. satunini (Zarudny, 1908), Crimean Peninsula, Caucasus, Transcaucasia and northwestern Iran to eastern Turkey
- C. c. raddei (Zarudny, 1908), northern Iran
- C. c. persicus (Blanford, 1873), Zagros Mountains
The two traditional subspecies found in the Canary Islands (teneriffae) and northwestern Africa from northern Morocco to northern Libya (ultramarinus) are distinctive. The Canary Islands subspecies has a black cap, and the African form has a blue back. Research is underway to split these populations into distinct species, with a peculiar "leapfrog" distribution:
- Afrocanarian Blue Tit/Ultramarine Tit, Parus ultramarinus Bonaparte, 1841 (La Palma, Hierro, Fuerteventura, Lanzarote, NW Africa);
- Canary Islands Blue Tit, Parus teneriffae Lesson, 1831.(Tenerife, La Gomera, Gran Canaria)
The former would contain three or four subspecies (palmensis, ombriosus and ultramarinus/degener), the latter the nominate P. t. teneriffae and P. t. hedwigae of Gran Canaria.
Research published in 2007 found that Blue Tits on the eastern Canary Islands of Fuerteventura and Lanzarote are indistinguishable from those in North Africa and so the subspsecies degener should be regarded as a synonym of ultramarinus.
Pleske's Tit (Cyanistes pleskei) is a common hybrid between this species and the Azure Tit in western Russia. The cap is usually darker than the Azure Tit, and the tail is paler than the Blue Tit.
A typical Blue Tit has an azure blue crown and dark blue line passing through the eye, and encircling the white cheeks to the chin, giving the bird a very distinctive appearance. The forehead and a bar on the wing are white. The nape, wings and tail are blue and the back is yellowish green. The underparts is mostly sulphur-yellow with a dark line down the abdomen - the yellowness is indicative of the number of yellowy-green caterpillars eaten, due to high levels of carotene pigments in the diet. The bill is black, the legs bluish grey, and the irides dark brown. The sexes are similar, but under ultraviolet light, males have a brighter blue crown.  Young Blue Tits are noticeably more yellow.
Distribution and habitat 
There are currently around 20–44 million pairs in Europe.
The Blue Tit and the related hybrids are considered native species in areas of the European continent with a mainly temperate or Mediterranean climate, and in parts of the Middle East and North Africa. These areas include the United Kingdom and most of the European Economic Area (except Malta, where they are considered vagrant, and Iceland, where they are absent), plus: Albania, Algeria, Armenia, Azerbaijan, Belarus, Bosnia and Herzegovina, Croatia, Georgia, Iran, Iraq, Jordan, Kazakhstan, Lebanon, Libya, Macedonia (former Yugoslav Republic), Moldova, Montenegro, Morocco, Russia, Serbia, Switzerland, Syria, Tunisia, Turkey and Ukraine.
Behaviour and ecology 
Blue and Great Tits form mixed winter flocks, and the former are perhaps the better gymnasts in the slender twigs. A Blue Tit will often ascend a trunk in short jerky hops, imitating a Treecreeper. As a rule the bird roosts in ivy or evergreens, but in harsh winters will nest wherever there is a suitable small hole, be it in a tree or nesting box. Blue tits are very agile and can hang from almost anywhere.
This is a common and popular European garden bird, due to its perky acrobatic performances when feeding on nuts or suet. It swings beneath the holder, calling "tee, tee, tee" or a scolding "churr".
The Blue Tit will nest in any suitable hole in a tree, wall, or stump, or an artificial nest box, often competing with House Sparrows or Great Tits for the site. Few birds more readily accept the shelter of a nesting box; the same hole is returned to year after year, and when one pair dies another takes possession. It is estimated by the RSPB that there are 3,535,000 breeding pairs in the UK.
The bird is a close sitter, hissing and biting at an intruding finger. In the South West of England such behaviour has earned the Blue Tit the colloquial nickname "Little Billy Biter".[by whom?] When protecting its eggs it raises its crest, but this is a sign of excitement rather than anger, for it is also elevated during nuptial display. The nesting material is usually moss, wool, hair and feathers, and the eggs are laid in April or May. The number in the clutch is often very large, but seven or eight are normal, and bigger clutches are usually laid by two or even more hens. It is not unusual for a single bird to feed the chicks in the nest at a rate of one feed every ninety (90) seconds during the height of the breeding season. In winter they form flocks with other tit species.
The Blue Tit is a valuable destroyer of pests, though it has not an entirely clean sheet as a beneficial species. It is fond of young buds of various trees, and may pull them to bits in the hope of finding insects. No species, however, destroys more coccids and aphids, the worst foes of many plants. It takes leaf miner grubs and green tortrix moths (Tortricidae). Seeds are eaten, as with all this family.
Blue Tits use songs and calls throughout the year. Songs are mostly used in late winter and spring to defend the territory or to attract mates. Calls are used for multiple reasons. Communication with other Blue Tits is the most important motivation for the use of calls. They inform one another on their location in trees by means of contact-calls. They use alarm-calls to warn others (including birds of other species such as the Great Tit, the European Robin or the Treecreeper) about the presence of predators in the neighbourhood. Scolding for example is used when a ground predator (e.g. Fox, Cat or Dog), a low flying predator or a perched Owl are noticed. Sometimes this is followed by mobbing behaviour in which birds gather together in flocks to counter a predator. The alarm-whistle warns other birds about the proximity of a Eurasian Sparrowhawk, a Northern Goshawk, a Common Buzzard or other flying predators that form a potential danger in the air. A series of high-pitched 'zeedling' notes are given by both partners before and during copulation. The begging-call is used by juveniles to beg for food from parents.
Blue Tits are able to culturally transmit learning to other Tit species. An example of this, dating from the 1920s, is the ability to open milk bottles with foil tops, to get at the cream underneath. Such behaviour has been suppressed recently by the gradual change of human dietary habits (low-fat or skimmed milk instead of full-fat), and the way of getting them (from a supermarket, instead of the milkman).
Predators and natural threats 
The small size of the blue tit makes it vulnerable to prey by larger birds such as Jays who catch the vulnerable fledglings when leaving the nest. The most important predator is probably the sparrowhawk, closely followed by the domestic cat. Nests may be robbed by mammals such as weasels and red squirrels and grey squirrels in the UK.
The successful breeding of chicks is dependent on sufficient supply of green caterpillars as well as satisfactory weather. Breeding seasons may be affected badly if the weather is cold and wet between May and July, particularly if this coincides with the emergence of the caterpillars on which the nestlings are fed.
Parasites and lifespan 
Blue Tits are known to be host to feather mites, and rarely lice and flat flies. In Europe the only feather mite species known to live on the Blue Tit host is Proctophyllodes stylifer. P. stylifer however seems to be of no concern to the bird as, until now, it is only known to feed on dead feather tissue. P. stylifer lives all its developmental stages, i.e. egg, larva, protonymph, tritonymph and adult, within the plumage of the same host. The usual sites where P. stylifer is encountered are the remiges and the rectrices of the bird where they can be found tandemly positioned between the barbs of the rachis.
The Blue Tit has an average life expectancy of one-and-a-half to three years. The longest recorded lifespans by country for the species are: 11 years 7 months in the Czech Republic, and 9 years 9 months 2 days in the United Kingdom.
Status and conservation 
The Blue Tit is classified as a Least Concern species on the IUCN Red List (version 3.1), and as a Green Status species, since 1996, by the Royal Society for the Protection of Birds in the United Kingdom.
Relationship with humans 
The Blue Tit has appeared in many stamps and ornaments. For example, the 2010 Birds of Britain series is the most recent appearance of the bird on a British stamp.
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- Hinde, RA (1952). The behaviour of the Great Tit (Parus Major) and some other related species. Behaviour (Suppl.) II: 1-201.
- Sasvári, Lajos (August 1979). "Observational learning in great, blue and marsh tits". Animal Behaviour 27 (3): 767–771. doi:10.1016/0003-3472(79)90012-5.
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- Stephens, Kate (2010), Birds of Britain I - A Presentation Pack, Royal Mail
Further reading 
- "393 - Blue Tit". Laboratorio Virtual Ibercaja. 9 May 2011. Retrieved 31 March 2013.
|Wikimedia Commons has media related to: Cyanistes caeruleus|
- The Royal Society for the Protection of Birds (Blue Tit)
- Blue Tit videos, photos & sounds on the Internet Bird Collection.