The male of the nominate subspecies, which is found throughout most of Europe, is all black except for a yellow eye-ring and bill and has a wide range of vocalisations; the adult female and juvenile have mainly brown plumage. This species breeds in woods and gardens, building a neat, mud-lined, cup-shaped nest. It is omnivorous, eating a wide range of insects, earthworms, berries, and fruits.
Both sexes are territorial on the breeding grounds, with distinctive threat displays, but are more gregarious during migration and in wintering areas. Pairs will stay in their territory throughout the year where the climate is sufficiently temperate. This common species has given rise to a number of literary and cultural references, frequently related to its melodious song.
It may not immediately be clear why the name "Blackbird", first recorded in 1486, was applied to this species, but not to one of the various other common black British birds, such as the Carrion Crow, Raven, Rook or Jackdaw. However, in Old English, and in modern English up to about the 18th century, "bird" was used only for smaller or young birds, and larger ones such as crows were called "fowl". At that time, the Blackbird was therefore the only widespread and conspicuous "black bird" in the British Isles. Until about the 17th century, another usual name for the species was ouzel, ousel or wosel (from Old English osle). Another variant occurs in Act 3 of Shakespeare's A Midsummer Night's Dream, where Bottom refers to "The Woosell cocke, so blacke of hew, With Orenge-tawny bill". The ouzel usage survived later in poetry, and still occurs as the name of the closely related Ring Ouzel (Turdus torquatus), and in Water Ouzel, an alternative name for the unrelated but superficially similar White-throated Dipper (Cinclus cinclus).
Two related Asian Turdus thrushes, the White-collared Blackbird (T. albocinctus) and the Grey-winged Blackbird (T. boulboul), are also named blackbirds, and the Somali Thrush (T. (olivaceus) ludoviciae) is alternatively known as the Somali Blackbird.
The icterid family of the New World is sometimes called the blackbird family because of some species' superficial resemblance to the Old World thrushes, especially this species, but they are not evolutionarily close, being closer to the New World warblers and tanagers. The term is often limited to smaller species with mostly or entirely black plumage, at least in the breeding male, notably the cowbirds, the grackles, and especially around 20 species with "blackbird" in the name, such as the Red-winged Blackbird and the Melodious Blackbird.
The taxonomy, especially of the Asian subspecies, is complex. The subspecies from most of the Indian subcontinent, simillimus, nigropileus, bourdilloni, spencei, and kinnissi, are small, only 19–20 centimetres (7.5–8 in) long, and have broad eye-rings. They also differ in proportions, wing formula, egg colour and voice from the other subspecies of the Blackbird. They are therefore sometimes considered a separate species, the Indian Blackbird (T. simillimus). The Himalayan subspecies maximus is strikingly different from the simillimus group, being relatively large at 23–28 centimetres (9–11 in) length. It differs from all other subspecies of the Blackbird by its complete lack of eye-ring and reduced song. It is therefore sometimes considered a full species, the Tibetan Blackbird (T. maximus). The remaining Asian subspecies, the relatively large intermedius and mandarinus, and the smaller sowerbyi, also differ in structure and voice, and may represent a third species, the Chinese Blackbird (T. mandarinus). Alternatively, it has been suggested that they should be considered subspecies of T. maximus, but they differ in structure, voice and the appearance of the eye-ring.
The Blackbird breeds in temperate Eurasia, North Africa, the Canary Islands, and South Asia. It has been introduced to Australia and New Zealand. Populations are sedentary in the south and west of the range, although northern birds migrate south as far as northern Africa and tropical Asia in winter. Urban males are more likely to overwinter in cooler climes than rural males, an adaptation made feasible by the warmer microclimate and relatively abundant food that allow the birds to establish territories and start reproducing earlier in the year.
Common over most of its range in woodland, the Blackbird has a preference for deciduous trees with dense undergrowth. However, gardens provide the best breeding habitat with up to 7.3 pairs per hectare (nearly three pairs per acre), with woodland typically holding about a tenth of that density, and open and very built-up habitats even less. They are often replaced by the related Ring Ouzel in areas of higher altitude.
The Blackbird occurs up to 1000 metres (3300 ft) in Europe, 2300 metres (7590 ft) in North Africa, and at 900–820 metres (3000–6000 ft) in peninsular India and Sri Lanka, but the large Himalayan subspecies range much higher, with T. m. maximus breeding at 3200–4800 metres (10560–16000 ft) and remaining above 2100 metres (6930 ft) even in winter.
This widespread species has occurred as a vagrant in many locations in Eurasia outside its normal range, but records from North America are normally considered to involve escapees, including, for example, the 1971 bird in Quebec. However, a 1994 record from Bonavista, Newfoundland has been accepted as a genuine wild bird, and the species is therefore on the North American list.
The Blackbird was introduced to Australia at Melbourne in the 1850s, but has expanded from its initial foothold in Melbourne and Adelaide to occur throughout south-eastern Australia, including Tasmania and the Bass Strait islands. The introduced population in Australia is considered a pest because it damages a variety of soft fruits in orchards, parks and gardens including berries, cherries, stone fruit and grapes. It is thought to spread weeds, such as blackberry, and may compete with native birds for food and nesting sites.
The introduced Blackbird is, together with the native Silvereye (Zosterops lateralis), the most widely distributed avian seed disperser in New Zealand. Introduced there along with the Song Thrush (Turdus philomelos) in 1862, it has spread throughout the country up to an elevation of , as well as outlying islands such as the Campbell and Kermadecs. It eats a wide range of native and exotic fruit, and makes a major contribution to the development of communities of naturalised woody weeds. These communities provide fruit more suited to non-endemic native birds and naturalised birds, than to endemic birds.
The bill’s appearance is important in the interactions of the Blackbird. The territory-holding male responds more aggressively towards models with orange bills than to those with yellow bills, and reacts least to the brown bill colour typical of the first-year male. The female is, however, relatively indifferent to bill colour, but responds instead to shinier bills.
As long as winter food is available, both the male and female will remain in the territory throughout the year, although occupying different areas. Migrants are more gregarious, travelling in small flocks and feeding in loose groups in the wintering grounds. The flight of migrating birds comprises bursts of rapid wing beats interspersed with level or diving movement, and differs from both the normal fast agile flight of this species and the more dipping action of larger thrushes.
Nominate T. merula may commence breeding in March, but eastern and Indian races are a month or more later, and the introduced New Zealand birds start nesting in August. The breeding pair prospect for a suitable nest site in a creeper or bush, favouring evergreen or thorny species such as ivy, holly, hawthorn, honeysuckle or pyracantha, and the female builds a neat cup-shaped nest from grasses and similar vegetation, which she then lines with mud or muddy leaves. She lays three to five (usually four) bluish-green eggs marked with reddish-brown blotches, heaviest at the larger end; the eggs of nominate T. merula are 2.9 x 2.1 centimetres (1.14 x 0.93 in) in size and weigh 7.2 grammes (0.25 oz), of which 6% is shell. Eggs of birds of the southern Indian races are paler than those from the northern subcontinent and Europe.
The female incubates for 12–14 days before the altricial chicks are hatched naked and blind. Fledging takes another 10–19 (average 13.6) days, with both parents feeding the young and removing faecal sacs. The young are fed by the parents for up to three weeks after leaving the nest, and will follow the adults begging for food. If the female starts another nest, the male alone will feed the fledged young. Second broods are common, with the female reusing the same nest if the brood was successful, and three broods may be raised in the south of the Blackbird's range.
Montane subspecies, such as T. maximus have a shorter breeding season, smaller clutches (2–4 eggs, averaging 2.86), but larger eggs than merula. They produce just one brood per year, and have a slightly shorter incubation period of 12–13 days, but a longer nestling period (16–18 days).
The first-year male Blackbird of the nominate race may start singing as early as late January in fine weather in order to establish a territory, followed in late March by the adult male. The male's song is a varied and melodious low-pitched fluted warble, given from trees, rooftops or other elevated perches mainly in the period from March to June, sometimes into the beginning of July. It has a number of other calls, including an aggressive seee, a pook-pook-pook alarm for terrestrial predators like cats, and various chink and chook, chook vocalisations. The territorial male invariably gives chink-chink calls in the evening in an (usually unsuccessful) attempt to deter other Blackbirds from roosting in its territory overnight. Like other passerine birds, it has a thin high seee alarm call for threats from birds of prey since the sound is rapidly attenuated in vegetation, making the source difficult to locate.
At least two subspecies, T. m. merula and T. m. nigropileus, will mimic other species of birds, cats, humans or alarms, but this is usually quiet and hard to detect. The large mountain races, especially T. m. maximus, have comparatively poor songs, with a limited repertoire compared with the western, peninsular Indian and Sri Lankan taxa.
The main predator of the Blackbird is the domestic cat, but foxes and predatory birds, such as the Sparrowhawk and other accipiters, also take this species when the opportunity arises. In contrast, there is little direct evidence to show that either predation of the adult Blackbirds or loss of the eggs and chicks to corvids, such as the European Magpie or Eurasian Jay, have a direct impact on population numbers.
This species is occasionally a host of parasitic cuckoos, such as the Common Cuckoo (Cuculus canorus), but this is minimal because the Blackbird recognizes the adult of the parasitic species and its non-mimetic eggs. The introduced merula Blackbird in New Zealand, where the cuckoo does not occur, has, over the past 130 years, lost the ability to recognize the adult Common Cuckoo but still rejects non-mimetic eggs.
As with other passerine birds, parasites are common. 88% of blackbirds were found to have intestinal parasites, most frequently Isospora and Capillaria species. and more than 80% had haematozoan parasites. Blackbirds spend much of their time looking for food on the ground where they can become infested with ticks, which are external parasites that most commonly attach to the head of a Blackbird. In France, 74% of rural Blackbirds were found to be infested with Ixodes ticks, whereas, only 2% of Blackbirds living in urban habitats were infested. This is partly because it is more difficult for ticks to find another host on lawns and gardens in urban areas than in uncultivated rural areas, and partly because ticks are likely to be commoner in rural areas, where a variety of tick hosts, such as foxes, deer and boar, are more numerous. Although, ixodid ticks can transmit pathogenic viruses and bacteria, and are known to transmit Borrelia bacteria to birds, there is no evidence that this affects the fitness of Blackbirds except when they are exhausted and rundown after migration.
The Blackbird was seen as a sacred though destructive bird in Classical Greek folklore, and was said to die if it consumed pomegranate. Like many other small birds, it has in the past been trapped in rural areas at its night roosts as an easily available addition to the diet, and in medieval times the conceit of placing live birds under a pie crust just before serving may have been the origin of the familiar nursery rhyme:
Sing a song of sixpence,
A pocket full of rye;
Four and twenty blackbirds baked in a pie!
When the pie was opened the birds began to sing,
Oh wasn't that a dainty dish to set before the king?
The Blackbird's melodious, distinctive song is the theme of the poem Adelstrop by Edward Thomas;
And for that minute a blackbird sangThe song is also recalled in the Beatles track Blackbird:
Close by, and round him, mistier,
Farther and farther, all the birds
Of Oxfordshire and Gloucestershire.
Blackbird singing in the dead of night,
Take these broken wings and learn to fly
All your life,
You were only waiting for this moment to arise.
The Blackbird, unlike many black creatures, is not normally seen as a symbol of bad luck, but R. S. Thomas wrote that there is "a suggestion of dark Places about it", and it symbolised resignation in the 17th century tragic play The Duchess of Malfi; an alternate connotation is vigilance, the bird's clear cry warning of danger.