Common Blackbird

Appearance

The Common Blackbird of the nominate subspecies ''T. m. merula'' is 23.5 to 29 centimetres in length, has a long tail, and weighs 80–125 grammes. 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.

Naming

The Common Blackbird was described by Linnaeus in the 10th edition his ''Systema Naturae'' in 1758 as ''Turdus merula''. The binomial name derives from two Latin words, ''turdus'', "thrush", and ''merula'', "blackbird", the latter giving rise to its French name, ''merle'', and its Scots name, ''merl''. There are about 65 species of medium to large thrushes in the genus ''Turdus'', characterised by rounded heads, longish pointed wings, and usually melodious songs. The Common Blackbird seems to be closest in evolutionary terms to the Island Thrush of Southeast Asia and islands in the southwest Pacific, which probably diverged from ''merula'' stock fairly recently.

Distribution

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.

Status

The Common Blackbird has an extensive range, estimated at 10 million square kilometres, 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, and is therefore evaluated as Least Concern.

Behavior

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.

Reproduction

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 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 in size and weigh 7.2 grammes, 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 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.

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.

Food

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.

Predators

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.