The Eurasian blue tit (Cyanistes caeruleus) is a diminutive and vibrant passerine, a member of the tit family, Paridae. It is distinguished by its striking blue and yellow plumage and compact stature.
This species exhibits an azure-blue crown with a dark blue line passing through the eye and encircling the white cheeks to the chin. The forehead and a wing bar are white, while the nape, wings, and tail are blue. The back is yellowish-green, and the underparts are predominantly sulphur-yellow with a dark abdominal line. Both sexes are similar, but males may exhibit a brighter blue crown under ultraviolet light.
Eurasian blue tits are found in temperate and subarctic Europe and the western Palearctic, favoring deciduous or mixed woodlands rich in oak. They are adaptable and can thrive in tree holes or nest boxes in various environments, including urban areas.
The species is widespread and commonly breeds across Europe, extending into parts of the Middle East. It is a resident bird, with populations found from Ireland and the United Kingdom to Iran and northern Turkey.
Eurasian blue tits are known for their agility and acrobatic feeding habits, often hanging upside down on the outermost branches. They form mixed winter flocks with other tit species and are adept at ascending tree trunks in short hops.
Their vocal repertoire includes songs and calls used for territory defense, mate attraction, and communication. Alarm calls may be used to warn of predators, and a series of high-pitched notes are associated with courtship and copulation.
Nesting occurs in suitable cavities, with a preference for holes in trees or artificial nest boxes. The species is socially monogamous but may engage in extra-pair copulations. Clutch size can be large, with eggs laid in April or May.
The Eurasian blue tit can be confused with the larger great tit, but the latter lacks the blue tit's distinctive blue and yellow coloring and eye line.
Primarily insectivorous, the Eurasian blue tit's diet consists of insects and spiders, with seeds and other plant-based foods consumed outside the breeding season. Caterpillars are particularly important for feeding nestlings.
The Eurasian blue tit is classified as Least Concern by the IUCN, indicating a stable population across its range. It is also considered a Green Status species by the Royal Society for the Protection of Birds in the UK.