The Eurasian blue tit (Cyanistes caeruleus), is certainly a bird that lives up to its name, adding a splash of color to the bird feeders of many a garden bird table. Formerly a denizen of deep dark woodland, it is a species that has adapted well to life from suburban gardens to urban parks and a wide variety of man-made habitats.
Growing up as a child of suburbia in the UK the blue tit was one of the first species that sparked an interest in birds, with its agile bird-table habits, rather gaudy bright azure blue, sulphur yellow and white plumage and its’ loud high-pitched ‘sisisudu’ calls this irascible little bird is hard not to notice.
Their mischievous and inquisitive nature has led to an amazing adaptability to a variety of food sources and habitats and their ever-amusing antics to a place in the hearts of those who enjoy feeding their garden birds across much of Europe.
Being a relatively common bird that readily takes to artificial nest boxes, the blue tit is perhaps one of the most well-studied birds in the world, with numerous scientific papers written about their breeding biology, ecology and population trends.
Quick facts
- Lifespan – 3 years on average
- Weight – 10-12 grams (0.35-0.42oz)
- Length – 10.5 -12cm (4.2-4.7 inches)
- Wingspan – 17-18cm (6.7-7.1 inches)
- Family – Paridae (Tits)
The Cyanistes family was elevated from a subgenus to a genus, after research into the mitochondrial DNA revealed they were an early offshoot of the family and consisted of three species that includes the blue tit, the closely related African blue tit (Cyanistes teneriffae) and Azure Tit (Cyanistes cyanus).
There are at least nine subspecies across the range with lots of interbreeding forming intergrades between the subspecies where their ranges overlap and also some interbreeding between the closely related Azure Tit to form a hybrid known as Pleske’s Tit.
The latin name first given by Carl Linnaeus was Parus caeruleus, with Parus being Tit and caeruleus dark blue in classical latin. However, the latin name was recently changed to Cyanistes caeruleus in 2005. Rather confusingly the new name literally translates as ‘dark blue dark blue’ withthe name coming from classical Greek ‘kuanos’ that means dark blue and the latin ‘caeruleus’ also meaning dark or azure blue.
The name of ‘titmose’ originates from the 14th century and is the Old English name for the bird. Both parts of the name come from Old Norse, ‘tit’ meaning small creature and ‘mase’ meaning small bird. The former spelling, “titmose”, gradually changed to ‘titmouse’ by the 16th century perhaps due to the similarity of ‘mose’ to mouse and their small size and quick scurrying movements. The name Tit is a further shortening of the name Titmouse.
Once commonly known colloquially as Tomtit, a shortening of the name Tom Titmouse, that name, was also used to describe other small bird species such as the Winter Wren (Troglodytes troglodytes), but has fallen out of common use. However, one species of Robin (Petroica macrocephala) in New Zealand, still bears the name given to it by early white settlers.
Gilbert White, one of the first well-known writers on natural history writing in the Natural History of Selbourne in the late 18th Century, also described the blue titmouse as the nun, perhaps in reference to the blue and white colours in the plumage. Another name given to the blue tit in Norfolk in the 18th Century was the ‘pickcheese’ as some had learned the habit of entering dairies to eat the cheese they could presumably smell.
In the United Kingdom another nickname for the blue tit that has fallen out of use is ‘Billy-biter’. A term coined by young lads in the South-West of England hoping to take eggs from a nest in the days when egg-collecting was still acceptable. This is due to their habit of biting fingers while hissing at an intruding finger into a nest, as the blue tit tends to sit tight and vociferously defend its eggs or chicks, rather than flee the nest.
Widely distributed across Europe (except northern Scandinavia and Iceland), parts of Asia Minor and the Middle East in areas with suitable habitat. There are estimated to be between 19 and 42 million pairs across their range. The population is stable and increasing and is considered as Least Concern by the IUCN.
Although largely resident, with no more than 1.2% of the population moving more than 20km (9 miles), some post-breeding dispersal movement may occur to find new territories, or during hard weather in search of food. Large-scale movements tend to be on the Eurasian landmass, usually from northern populations moving to the south-west.
There have been several ringing recoveries in the UK from mainland Europe, including two birds from Norway indicating some birds make it across the North Sea some years. However, with more provision of food in Scandinavian gardens and generally warmer winters these hard-weather movements are becoming less frequent.
This largely sedentary species breeds in a wide variety of natural and semi-natural habitats, including deciduous and mixed woodland, as well as parks and gardens even in quite large towns and cities. They are especially prevalent in deciduous oak woodland.
Outside of the breeding season this species can be found in a wide variety of habitats, foraging in woodland, parks, hedgerows, gardens, reedbeds and even ditches in search of both insect and non-insect food.
The blue tit diet is mainly insect-based from spring through to autumn, though relies less on insects and more on seeds and other sources in the winter. They feed on the caterpillars of a wide variety of moth species, as well as leaf miner grubs, coccids and aphids, many of which are a bane to farmers and gardeners.
Blue Tits will also less favorably feed on the buds of some tree species in the spring, as well as seeds, especially beech mast in the autumn and winter.
As well as natural food sources, they are well-adapted to utilizing a wide variety of food sources provided by people such as coconut, peanuts, various seeds, suet, fat balls, fallen or rotting fruit, the cream from bottles of milk and even rotting flesh.
During the autumn and winter blue tits form mixed species feeding flocks with other species such as Long-tailed Tit (Aegithalos caudatus, Great Tit (Parus major), Goldcrest (Regulus regulus), Eurasian Treecreeper ( Certhia familiaris) and warblers such as Chiffchaff (Phylloscopus collybita). They actively search together for insect prey in the autumn and early winter and blue tits will also visit bird feeders alongside Great Tit and Long-tailed Tit among other species to feed on peanuts, fat and seeds. They are quite aggressive and will drive away each other or other species from bird feeders when food is scarce.
They are incredibly agile and will often ascend a trunk in short jerky hops, rather like a Treecreeper and are able to hang upside down from twigs to glean insects or feeders picking away for other foodstuffs.
They can become very tame at bird feeders and are fearless, only moving away from the feeders at the close approach of people. They will feed on the ground or even close to houses, searching windows for insects and spiders in the window frames or putty and have been known to enter houses.
Although traditionally blue tits roost in ivy or evergreens, they are increasingly being found to roost communally in nest boxes and will seek shelter inside man-made structures with a small entrance hole.
The blue tit usually begins courtship from late winter, singing and establishing pairs and territories on warm late winter days. Males will display to females with their crown raised, the bright blue attracting the females to a potential mate.
Studies have shown that although largely faithful to one mate, they may ‘divorce their partners’ if their partner turns up late to the annual breeding season and can mate outside the pair. However, the vast majority stay together long-term and this is thought to be beneficial because it means they can focus on breeding and parenting rather than having to look for new mates.
They begin nesting in late April and will nest in any suitable hole in a tree, wall, or stump. Few species take more readily though to artificial nest boxes and have even been found to nest in other man-made structures such as lamp-posts and mail boxes, often competing with other species such as the Great Tits for such sites.
Blue tits are very site faithful and will return to the same nesting site, and if one pair dies out, the site is usually quickly taken over by a new pair. They line the nest with various grasses, moss, animal hair, wool and feathers.
The female usually has a single brood, but will relay eggs if the first set of eggs are lost to predators or poor weather. The female lays between 7 and 13 eggs, but can lay up to 19 eggs individually and sometimes more than one female can lay in a nest. The size of the egg is dependant mainly on the size of individual females, but can also be affected by habitat with smaller eggs found at higher altitudes.
During the incubation period of 13-15 days, the female blue tits perform most of the incubation, however the male feeds the female during this time.
Once all eggs are hatched both parents feed the young and female nest attendance and male feeding rate is higher in the morning, declining throughout the day. It usually takes around three weeks for chicks to fledge and the chicks will quadruple in size during that period.
Breeding success is dependent not only on food availability, but also on the efficiency of the parents to feed their young, and at the height of the breeding season the chicks can be fed at a rate of one feed every 90 seconds. In years with abundant food productivity is very high, but in poor years they may have very little success.
During the incubation period and on fledging there are various predators that can take eggs or nestlings, including corvid species such as Jay as they leave the nest, to Great Spotted Woodpecker that have been known to drill out nest holes to access fledglings. Several mammals such as Stoat, Weasel, Red Squirrel and even the introduced Grey Squirrel in the United Kingdom will take chicks if they can gain access to the nest.
The major threat to young blue tits post-fledging is starvation, with studies showing some 21% of young birds found dead within 30 days. If they can find enough food on fledging, then the major threats to their survival other than food shortage or weather are domestic cats and birds of prey especially the Eurasian Sparrowhawk.
In one study between 18-27% of young blue tit fatalities appeared to be attributable to predation by Sparrowhawks. However, a pair of blue tits only needs to raise one chick per pair to keep the population stable and replace adult fatalities.
Studies have shown that Sparrowhawk predation doesn’t adversely affect the blue tit population overall, and it either remains stable or increases even with increased numbers of Sparrowhawks breeding.
It is still unclear what the impact of domestic cat predation is on blue tit populations, but some 42% of blue tit ringing recoveries come from birds found dead that were killed by cats. Very few studies have been conducted on the impact of domestic cats, but it is likely that at least locally in areas with high densities of cats that fledging birds such as young blue tits may suffer slightly higher than average mortalities, although clearly not negatively impacting on the population as a whole.
Blue tits are not hunted by man for food or sport, and due to their largely resident status, they do not face the threat of hunters, lime traps and nets that other long-distance small bird migrants face.
Males tend to be brighter in plumage than females, especially on the crown, which can be seen under ultraviolet light. However, in some subspecies the females are as bright as the males and cannot always safely be identified as male or female on plumage alone.
It is believed that brightness of the plumage increases with each molt. The yellowish-green pigmentation is supposedly due to high levels of carotene pigments in the diet from the yellowy-green caterpillars eaten.
There are also clinal differences between subspecies, with northerly subspecies tending to be darker than the southerly races.
The adult blue tit is unmistakable, a small compact bird with short wings, medium-length square tail and striking head pattern of azure-blue crown, white forehead and broad white supercilium above a dark blue eye-stripe, dark blue bib and a thin dark blue line encircling the large white cheeks from the chin to the nape. The mantle and rump are moss-green, but wings and tail ultramarine blue except for a single short white wing-bar. The underparts are mostly sulphur-yellow with a dark line down the abdomen.
The bill is black, the legs bluish grey, and the irides dark brown.
As adult, but juveniles have a duller plumage overall, with yellow cheeks, a yellowish wingbar and no dark bib or line encircling the cheek. Over the course of the first autumn the juvenile gradually attains adult plumage.
A very vocal species. The song is mainly heard between January and June, but blue tits sing and use calls throughout the year. The song, consists of a series of sharp drawn-out notes followed by a lower-pitched trill of ‘siiuuh siiuh si-suurrr’ and two short repeated phrases of ‘si-surrr, si-si-surrr’ are mostly used in late winter and spring to defend the territory or to attract mates. The song is often given with raised crown feathers to attract a mate.
The blue tit has various calls it uses for communication, with the ‘sisidu’ and ‘sisisi’ contact calls used to indicate their location to others, and the harsher scolding ‘ki ki kur,’ or ker’r’r’r’r’ ek-ekek’ alarm-calls are used to warn other blue tits and bird species within feeding flocks or in woodland or gardens of the presence of ground or aerial predators. These same alarm calls are also used when groups of small birds, mob day-roosting predators such as Tawny Owl.
A series of high-pitched ‘zeedling’ notes are given by both partners before and during copulation and the loud begging-call of juveniles are used to get both parents to regurgitate food.
Blue tits are one of the few species closely associated with people and can be found in close proximity to humans and human habitation and this association goes back a long way. Even in the 18th century blue tits were recorded as being a great frequenter of houses. Gilbert White recorded the species as being a vast admirer of suet and as such haunt butcher’s shops. As previously mentioned, some blue tits in 18th Century England learnt to enter dairies and eat cheese.
This close association with man perhaps most famously dates back to the 1920s, when the ability to open the foil tops of milk delivered to the doorstep, to get at the cream underneath was first noted. This behavior was perhaps as a response to milk being delivered in this way on a large scale and less food being left out in gardens between the wars and was continued into the 1980’s. From the 1990’s onwards shopping and dietary habits changed with less people having milk delivered to the doorstep and more semi-skimmed and skimmed milk being consumed.
Other forms of learned behavior, which perhaps derived from the instinct to strip bark from trees in search of insects, also developed into a tendency to attack man-made materials on and in houses, such as the straws from thatch on a roof, putty from window frames, even the stucco and wallpaper inside houses. They were even recorded as entering houses and tearing at paper cartons, magazines and even lampshades perhaps in a fearless search for food.
Gilbert White also recorded a young boy who wanted to catch these beautiful little birds using their love of fat to capture them by baiting a snap mousetrap with tallow or suet. This rather threatening habit, later turned to people feeding birds from the later 19th Century onwards for pleasure and blue tits quickly adapted to exploiting the suet, coconuts and other foodstuffs people put out.
As well as artificial feeding, the blue tit has also learnt to use nest-boxes put up by man, not only for nesting, but also increasingly as a roosting place during the winter months as alternative to natural sites.
Although largely of benefit to humans in terms of eating large numbers of pest insect species, and so therefore not persecuted much by man, they will pull apart the young buds of certain tree species in the search for insect prey and will eat ripe fruit on trees such as apples and pears.
The longest-lived blue tit was recorded in the Czech Republic and it was 11 years old, nearly four times the average lifespan of the species.
They are so common in gardens in the United Kingdom that they appear in 98% of all gardens surveyed.
Sean Minns is a British birder and ornithologist with nearly 40 years in the field. He enjoys learning about the behaviour of birds first-hand, especially seabirds, is interested in the conservation of them and their habitats worldwide and has travelled to over 40 countries observing, studying and photographing them any chance he gets.