# UKBirds

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## Blackbird

### Turdus merula

The Common Blackbird (Turdus merula) is a species of true thrush. It is also called Eurasian Blackbird (especially in North America, to distinguish it from the unrelated New World blackbirds), or simply Blackbird, where this does not lead to confusion with a similar-looking local species. It breeds in Europe, Asia, and North Africa, and has been introduced to Australia and New Zealand. It has a number of subspecies across its large range; a few of the Asian subspecies are sometimes considered to be full species. Depending on latitude, the Common Blackbird may be resident, partially migratory or fully migratory.
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 rich melodious song; the adult female and juvenile have mainly dark 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 and conspicuous species has given rise to a number of literary and cultural references, frequently related to its song.
The Common Blackbird of the nominate subspecies T. m. merula is 23.5 to 29 centimetres (9.25 to 11.4 in) in length, has a long tail, and weighs 80-125 grammes (2.8 to 4.4 oz). The adult male has glossy black plumage, blackish-brown legs, a yellow eye-ring and an orange-yellow bill. The bill darkens somewhat in winter. The adult female is sooty-brown with a dull yellowish-brownish bill, a brownish-white throat and some weak mottling on the breast. The juvenile is similar to the female, but has pale spots on the upperparts, and the very young juvenile also has a speckled breast. Young birds vary in the shade of brown, with darker birds presumably males. The first year male resembles the adult male, but has a dark bill and weaker eye ring, and its folded wing is brown, rather than black like the body plumage.
The Common 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 Common 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 Common Blackbird occurs up to 1000 metres (3300 ft) in Europe, 2300 metres (7590 ft) in North Africa, and at 900-1820 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 Common Blackbird has an extensive range, estimated at 10 million square kilometres (3.8 million square miles), and a large population, including an estimated 79 to 160 million individuals in Europe alone. The species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e., declining more than 30% in ten years or three generations), and is therefore evaluated as Least Concern. In the western Palaearctic, populations are generally stable or increasing, but there have been local declines, especially on farmland, which may be due to agricultural policies that encouraged farmers to remove hedgerows (which provide nesting places), and to drain damp grassland and increase the use of pesticides, both of which could have reduced the availability of invertebrate food.
The Common 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 Common 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 1,500 metres (4,921 ft), 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 male Common Blackbird defends its breeding territory, chasing away other males or utilising a "bow and run" threat display. This consists of a short run, the head first being raised and then bowed with the tail dipped simultaneously. If a fight between male Blackbirds does occur, it is usually short and the intruder is soon chased away. The female Blackbird is also aggressive in the spring when it competes with other females for a good nesting territory, and although fights are less frequent, they tend to be more violent.
The bill's appearance is important in the interactions of the Common 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.
The male Common Blackbird attracts the female with a courtship display which consists of oblique runs combined with head-bowing movements, an open beak, and a "strangled" low song. The female remains motionless until she raises her head and tail to permit copulation. This species is monogamous, and the established pair will usually stay together as long as they both survive. Pair separation rates of up to 20% have been noted following poor breeding. Although socially monogamous, there have been studies showing as much as 17% extra pair paternity.
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. Sometimes the birds will nest in sheds or outbuildings where a ledge or cavity is used. The cup-shaped nest is made with grasses, leaves and other vegetation, bound together with mud. It is built by the female alone. 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 nest is often ill-concealed compared with those of other species, and many breeding attempts fail due to predation. 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 Common Blackbird's range.
Montane subspecies, such as T. merula maximus have a shorter breeding season, smaller clutches (2-4 eggs, averaging 2.86), but larger eggs than nominate 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).
A Common Blackbird has an average life expectancy of 2.4 years, and, based on data from bird ringing, the oldest recorded age is 21 years and 10 months.
The first-year male Common 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 Common Blackbird is omnivorous, eating a wide range of insects, earthworms, seeds and berries. It feeds mainly on the ground, running and hopping with a start-stop-start progress. It pulls earthworms from the soil, usually finding them by sight, but sometimes by hearing, and roots through leaf litter for other invertebrates. Small vertebrates such as frogs, tadpoles and lizards are occasionally hunted. This species will also perch in bushes to take berries and collect caterpillars and other active insects. Animal prey predominates, and is particularly important during the breeding season, with windfall apples and berries taken more in the autumn and winter. The nature of the fruit taken depends on what is locally available, and frequently includes exotics in gardens. In northern India, banyan and mulberry fruits are frequently eaten, with Erythrina and Trema species featuring further south.
Near human habitation the main predator of the Common Blackbird is the domestic cat, with newly-fledged young especially vulnerable. Foxes and predatory birds, such as the Sparrowhawk and other accipiters, also take this species when the opportunity arises. However, 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 an 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 Common 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 Common Blackbirds were found to have intestinal parasites, most frequently Isospora and Capillaria species. and more than 80% had haematozoan parasites (Leucocytozoon, Plasmodium, Haemoproteus and Trypanosoma species).
Common 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 run down after migration.
The Common Blackbird is one of a number of species which has unihemispheric slow-wave sleep. One hemisphere of the brain is effectively asleep, while a low-voltage EEG, characteristic of wakefulness, is present in the other. The benefit of this is that the bird can rest in areas of high predation or during long migratory flights, but still retain a degree of alertness.