Eurasian blue tit

Name and taxonomy

Carl Linnaeus described the blue tit in 1758, in the tenth edition of Systema Naturae. He gave it the name Parus caeruleus, and the type locality is Sweden. Parus is the classical Latin word for a tit, and caeruleus means dark blue. Conrad Gesner had already used the same Latin words in his Historiae animalium of 1555. The modern genus Cyanistes takes its name from kuanos, an Ancient Greek word for dark blue.

The English word titmouse goes back to the 14th century. It joins mase, an old name for the bird, with tit, a word for anything small. Spelling drift turned mose into mouse during the 16th century. Nine subspecies are recognised, and they differ only slightly in the shade of the plumage. The differences run in a gradual cline rather than in sharp steps.

Evolution and relatives

The blue tit belongs to Paridae, the family of tits, titmice and chickadees. That family sits within the songbirds, the largest group of perching birds. A 2005 study of mitochondrial DNA showed that Cyanistes split early from the other tits. Before that work the birds were placed in the large genus Parus. Cyanistes now holds three birds: this species, the azure tit, and the African blue tit of the Canaries.

Ornithologists once treated the African bird as part of this species. Where the blue tit meets the azure tit in western Russia, the two interbreed. The hybrid is known as Pleske's tit and is common in that region. A hybrid may look like an azure tit with less white in the tail and a yellow tinge below. Other hybrids look like blue tits with whitish underparts.

Appearance

The blue tit is 10.5 to 12 cm long and spans 17.5 to 20 cm across the wings. It weighs about 11 g, and the two sexes are the same size. The crown is a strong blue, and a dark blue line runs through the eye. That line rings the white cheeks and chin, which gives the face its clean pattern. The forehead is white, and a white bar crosses the wing. Blue covers the nape, the wings and the tail, while the back is a yellowish green.

The underparts are sulphur yellow, with a dark line down the middle of the belly. A stronger yellow shows that the bird has eaten many green caterpillars. The pigment behind the colour comes from carotene in that food. The bill is black and short, the legs are bluish grey, and the eyes are dark brown. A young bird is yellower overall, with softer contrasts and yellow cheeks. It looks much like an adult by September, though some wing markings last into the next spring.

To a human eye the sexes look alike. Under ultraviolet light the crown of a male shines brighter than the crown of a female. Blue tits see ultraviolet light, so the difference is probably plain to them.

Habitat and range

The blue tit is a resident breeder across temperate and subarctic Europe. Its range reaches east into western Asia and south into parts of the Middle East. It is native to Ireland, the United Kingdom and nearly all of the European Union. It also breeds in Turkey, the Caucasus states, Iran, Iraq, Syria, Jordan and Russia. It is absent from Iceland and reaches Malta only as a stray. GBIF holds occurrence records from 72 countries.

The preferred habitat is broadleaved or mixed woodland with a good share of oak. Oaks carry the caterpillars that the chicks need, so the bird probably depends on them. In Britain the species also lives in hedges, parks, gardens and town centres. Most birds stay in one place all year and do not migrate. Since 1980 the northern edge of the range has moved 500 kilometres up through Fennoscandia.

Diet and feeding

The blue tit eats mostly insects and spiders, with other small invertebrates as well. Springtails, grasshoppers, damselflies, earwigs, moths and lacewings all appear on the list. Green caterpillars matter most, because the chicks are raised on them. Outside the breeding season the bird also takes seeds and fruit. It searches inside opening buds, and it strips the bark of hazel to reach hidden insects.

The bird feeds among the thinnest twigs, often hanging upside down. It rarely hovers, and it seldom feeds on the ground. At a bird table it takes bread, cheese, fat and seeds, and it favours sunflower. A large seed is carried to a branch and held under one foot while the bill hammers it open. Garden feeders now supply peanuts, fat balls and sunflower hearts through the winter. That extra food probably helps small birds through the coldest weeks.

Behaviour and social life

In winter blue tits join mixed flocks with great tits and other small birds. A flock moves through the wood together, and it probably finds food faster than one bird could. The blue tit is the better balancer on slender twigs. It climbs a trunk in short jerky hops, in the manner of a treecreeper. It roosts in ivy or an evergreen, and in hard weather it uses any small hole it can find.

The species is a favourite at garden feeders because of its quick acrobatic style. It swings under a feeder while calling a thin tee, tee, tee or a scolding churr. Blue tits also chase each other around a garden through the day. Great tits and house sparrows are the main rivals for both food and holes. The larger great tit probably wins most direct contests.

British blue tits learned to open the foil caps of doorstep milk bottles from the 1920s. The habit spread from bird to bird, which makes it a clear case of learning in a wild animal. It has since faded, because doorstep delivery and full-fat milk both grew rare. The same instinct to strip bark now peels thatch, wallpaper, stucco and window putty.

Communication and senses

Blue tits sing and call all through the year. Song is heard mostly in late winter and spring, to hold a territory or to attract a mate. Contact calls tell other blue tits where each bird is among the branches. Alarm calls warn of a predator, and great tits, robins and treecreepers listen to them too. A scolding call answers a fox, a cat, a dog or a perched owl. Birds often gather and mob the intruder after that call.

A thin whistle warns of a hunter in the air, such as a sparrowhawk or a buzzard. A pair gives high zeedling notes before and during mating. Chicks beg with calls that change as they grow. Early calls are soft and pure, and later ones are lower and more like a hiss. Traffic noise can mask those calls, which may harm chicks at some ages more than others. Ultraviolet vision helps a blue tit tell a male, a female and a young bird apart.

Reproduction and life cycle

A pair will nest in almost any hole, in a tree, a wall, a stump or a box. Nesting starts in late March, and the same hole often serves year after year. When one pair dies, another moves in. The female does nearly all the building, from moss, wool, hair and feathers. Blue tits are socially monogamous, but both sexes mate outside the pair as well.

Laying falls in April or in May, and a clutch holds seven or eight eggs. Single females in Britain have laid verified clutches of 14, and some sources give up to 16. Clutch size changes with latitude and with the local ground. Each egg is 14 to 18 millimetres long and 10.7 to 13.5 mm wide. A whole clutch can weigh 1.5 times as much as the mother. Larger eggs come from larger females, and higher ground yields smaller ones.

The female sits alone for about 15 days while the male brings her food. She sits tight and hisses at a hand that reaches into the box. At the peak of the season a single parent may deliver food every 90 seconds. Both parents work hardest in the morning and slow through the day. Chicks stay in the hole for about three weeks before they fly. Warmer springs have moved laying earlier and made a second brood more likely.

Ringing data from Britain give a first-year survival rate of 38%. Adults that pass their first year survive at 53% a year. A bird that reaches breeding age can expect about 3 more years. The oldest British bird was ringed in Bedfordshire and lived 10 years and 3 months. The record for the species stands at 14.6 years.

Predators and threats

A blue tit is small enough for many hunters to take. The Eurasian sparrowhawk and the domestic cat are probably the two that kill the most. Jays catch fledglings in the days after they leave the hole. Weasels, red squirrels and introduced grey squirrels rob nests in Britain. Feather mites live in the plumage, and lice and flat flies turn up now and then. The only European feather mite known from the species is Proctophyllodes stylifer.

That mite eats dead feather tissue and appears to do the bird no harm. The bigger risk is the weather during the breeding season. A cold wet spell between May and July can ruin a brood. The damage is worst when the bad weather lands on the caterpillar flush. Chicks need a steady supply of green caterpillars to survive. Traffic noise near a nest may also make it harder for parents to hear begging chicks.

Population and conservation

Europe holds about 20 to 44 million pairs of blue tits. The United Kingdom alone holds around 3.4 million pairs. The long-term European trend is upward, with a rise of 30 per cent between 1980 and 2016. The UK population has grown by 21% since 1970. The range limit has also shifted 500 km north in Fennoscandia.

The IUCN lists the species as Least Concern. The Royal Society for the Protection of Birds has placed it on the Green list since 1996. Green is the lowest level of concern in the United Kingdom. Warmer springs may bring gains and risks together for the species. Earlier laying may miss the caterpillar peak if the two dates shift at different rates. Nest boxes in gardens and woods add holes where old trees have gone.

Relationship with humans

Few wild birds live so close to people in Europe. The blue tit visits garden feeders all winter and nests in boxes on house walls. Householders put out peanuts, fat balls, mixed seed and sunflower hearts for it. Conservation groups advise feeding in winter, when natural food runs short. A box with a small hole shuts out larger birds and probably suits this species best.

The bird also causes small nuisances around a house. It pecks at thatch, wallpaper, stucco and putty as it would peel bark. It once opened the milk left on British doorsteps. Nest boxes with cameras appear often on garden wildlife television. Ringing schemes have followed blue tits for decades and supply much of what we know.

In culture and myth

Almost every European language names the bird for its colour. German has Blaumeise, French Mésange bleue, Dutch Pimpelmees and Spanish Herrerillo común. Italian uses Cinciarella and Danish uses Blåmejse. The Latin name repeats the colour twice, in Cyanistes and in caeruleus. Related birds in North America are chickadees, a name copied from their alarm call.

In southwest England the blue tit is the Billy Biter. The name comes from the sitting female, who hisses and bites at a hand in the box. A raised crest looks like anger, but it also appears in courtship. The milk bottle story of the 1920s is likely the most repeated blue tit tale of all. The bird appears on stamps and ornaments, most recently in a 2025 British Garden Wildlife set.