thumb|235px|Eurasian blue tit on the ground, April.
The Eurasian blue tit (Cyanistes caeruleus) is a small passerine bird in the tit family, Paridae. It is easily recognised by its blue and yellow plumage and small size.
The Eurasian blue tit is a widespread and common resident breeder throughout temperate and subarctic Europe and parts of western Asia. It inhabits deciduous or mixed woodlands, often with a high proportion of oak, and it is usually non-migratory. They typically nest in tree holes but readily adapt to using nest boxes when necessary. Their main rivals for nests and in the search for food are the larger, somewhat more common great tits (Parus major).
The Eurasian blue tit's diet consists mainly of insects and spiders. Outside of the breeding season, they also eat seeds and other plant-based foods. These birds are known for their acrobatic abilities; they can grip the outermost branches of trees and shrubs and hang upside down while searching for food.
Taxonomy
The Eurasian blue tit was first described by Carl Linnaeus in 1758 in the 10th edition of his Systema Naturae under the binomial name Parus caeruleus. Two centuries earlier, before the introduction of the binomial nomenclature, the same Latin name had been used by the Swiss naturalist Conrad Gesner when he described and illustrated the blue tit in his Historiae animalium of 1555. The genus Cyanistes now contains three species, the Eurasian blue tit, the African blue tit, and the azure tit.
- C. c. obscurus – <small>(Pražák, 1894)</small>: found in Ireland, Britain and Channel Islands
Description
The Eurasian blue tit is usually long with a wingspan of for both sexes, and weighs about .
Blue tits can also see in ultraviolet light, which is one of the ways they can distinguish between male, female and juvenile birds. The cap of a male is a more intense shade of blue than that of a female or chick.
Distribution and habitat
thumb|Blue tit displaying aggression during [[Bird ringing|ringing]]
thumb|Blue tit recovering from a window strike, Czech Republic
There are currently around 20 to 44 million pairs in Europe.
Behaviour and ecology
Eurasian blue tits and great tits form mixed winter flocks, and the former are perhaps better at balancing on slender twigs. A Eurasian blue tit often ascends a tree trunk in short, jerky hops, reminiscent of a treecreeper. The bird usually roosts in ivy or evergreens, but in harsh winters it will roost wherever it can find a suitable small hole, whether in a tree or a nesting box. They are very agile and can hang from almost anywhere.
It is a common and popular European garden bird, due to its perky acrobatic performances when visiting bird feeders. It swings beneath the feeder, calling "tee, tee, tee" or a scolding "churr".
Breeding
<gallery>
File:Cyanistes caeruleus -Norfolk, England -adult feeding chick-8.jpg|Feeding the young at a nest box in England
File:Blue Tit Nest 06-05-12 (7003304998).jpg|Eggs in a nest in England
File:20120606 182000 Side w.jpg|Young inside a nestbox in Nittedal, Norway
File:PimpelMezen Voeren Jongen.webm|Feeding young
</gallery>
The Eurasian blue tit will nest in any suitable hole, whether in a tree, wall, or stump, or in an artificial nest box. They often compete with house sparrows or great tits for these sites. Few birds are more likely to accept the shelter of a nesting box, and the same hole is often used year after year. When one pair dies, another takes its place.
During the incubation period, the female blue tit does all of the incubating, while the male feeds her. During the nestling period, both female nest attendance and male feeding rates are higher in the morning, declining throughout the day. Although blue tits are socially monogamous, they regularly engage in extra-pair copulations with other individuals.
right|thumb|Juvenile in [[Pimlico, London]]
Eggs are long and wide. Egg size appears to depend mostly on the size of individual females and secondarily on habitat, with smaller eggs found at higher altitudes. The clutch's total weight can be 1.5 times as heavy as the female bird.
Eurasian blue tits sit closely on their nests, hissing and biting at any intruding fingers. In the southwest of England, this behaviour has earned the species the colloquial nickname "Little Billy Biter" or "Billy Biter". When protecting its eggs, it raises its crest, but this is a sign of excitement rather than anger, as it is also elevated during the 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 eggs are normal. Clutch size varies with latitude and other geographic parameters. In some locations, larger clutches may be laid by two or even more hens, but single-hen clutches of 14 have been verified in the UK. During the height of the breeding season, it is not unusual for a single bird to feed the chicks in the nest at a rate of one feeding every 90 seconds. In winter, they form flocks with other tit species.
An analysis of ring-recovery data in Britain revealed that the survival rate for juveniles in their first year was 38%, compared to an annual survival of 53% for adults.
Voice
thumb|left|Calls of a blue tit
Eurasian blue tits use songs and calls throughout the year. Songs are mostly performed in late winter and spring to defend the territory or to attract mates. Calls are used for multiple reasons, The information conveyed by begging calls can be masked by anthropogenic noise, and the age-related variation in calls may mean some phases of nestling development are more vulnerable to this disruption than others.
Learned behaviour
An interesting example of culturally transmitted learning in birds is the phenomenon, dating from the 1920s, of blue tits teaching one another to open traditional British milk bottles with foil tops to access the cream underneath. The species is classified as a of least concern in the Red list of the International Union for Conservation of Nature,
References
Sources
External links
- Feathers of Eurasian blue tit (Parus caeruleus)
- Blue tit improving the hollow entrance