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 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 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. , 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 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. Such behaviour has since been gradually suppressed due to the declining popularity of both full-fat milk and
milk delivery. In addition, the instinct to strip bark from trees in search of insects has developed into a tendency to peel building materials such as
thatch,
wallpaper,
stucco and window
putty.
Predators and natural threats The small size of the Eurasian blue tit makes it vulnerable to predation by larger birds such as
jays, which catch the vulnerable fledglings when they leave the nest. The most important predators are probably the
Eurasian sparrowhawk, closely and the
domestic cat. Nests may also be robbed by mammals such as
weasels and
red squirrels, as well as introduced
grey squirrels in the UK. Successful chick breeding depends on a sufficient supply of green
caterpillars, as well as favourable weather. Breeding seasons may be badly affected if the weather is unseasonably cold and wet between May and July, particularly if this coincides with the emergence of
caterpillars on which the nestlings are fed.
Parasites Eurasian blue tits are known to be host to feather
mites, and occasionally
lice and
flat flies. In Europe, the only feather mite species known to live on blue tits is
Proctophyllodes stylifer. However, this mite does not appear to cause any harm to the bird, as it is only known to feed on dead feather tissue.
P. stylifer lives through 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 in the remiges and the rectrices of the bird where they can be found randomly positioned between the barbs of the rachis. == Status and conservation ==