The Song Thrush breeds in forests, gardens and parks, and is partially migratory with many birds wintering in southern Europe, North Africa and the Middle East. Although it is not threatened globally, there have been serious population declines in parts of Europe, possibly due to changes in farming practices.
The Song Thrush builds a neat mud-lined cup nest in a bush or tree and lays four or five dark-spotted blue eggs. It is omnivorous and has the habit of using a favourite stone as an "anvil" on which to smash snails. Like other perching birds (passerines), it is affected by external and internal parasites and is vulnerable to predation by cats and birds of prey.
The Song Thrush (as represented by the nominate subspecies T. p. philomelos) is 20 to 23.5 centimetres (8 to 9.25 in) in length and weighs 50–107 grammes (1.8 to 3.8 oz). The sexes are similar, with plain brown backs and neatly black-spotted cream or yellow-buff underparts, becoming paler on the belly. The underwing is warm yellow, the bill is yellowish and the legs and feet are pink. The upperparts of this species become colder in tone from west to east across the breeding range from Sweden to Siberia. The juvenile resembles the adult, but has buff or orange streaks on the back and wing coverts.
The Song Thrush has a short, sharp tsip call, replaced on migration by a thin high seep, similar to the Redwing's call but shorter. The alarm call is a chook-chook becoming shorter and more strident with increasing danger. The male's song, given from trees, rooftops or other elevated perches, is a loud clear run of musical phrases, repeated two to four times, filip filip filip codidio codidio quitquiquit tittit tittit tereret tereret tereret, and interspersed with grating notes and mimicry. It is given mainly from February to June by the Outer Hebridean race, but from November to July by the more widespread subspecies. For its weight, this species has one of the loudest bird calls.
Distribution and habitatEdit
The Song Thrush breeds in most of Europe (although not in the greater part of Iberia, lowland Italy or southern Greece), and across the Ukraine and Russia almost to Lake Baikal. It reaches to 75oN in Norway, but only to about 60oN in Siberia. Birds from Scandinavia, Eastern Europe and Russia winter around the Mediterranean, North Africa and the Middle East, but only some of the birds in the milder west of the breeding range leave their breeding areas.
BehaviourEditThis is a monogamous territorial species, and in areas where it is fully migratory, the male re-establishes its breeding territory and starts singing as soon as he returns. In the milder areas where some birds stay year round, the resident male remains in his breeding territory, singing intermittently, but the female may establish a separate individual wintering range until pair formation begins in the early spring.
During migration, the Song Thrush travels mainly at night with a strong and direct flight action. It flies in loose flocks which cross the sea on a broad front rather than concentrating at short crossings (as occurs in the migration of large soaring birds), and calls frequently to maintain contact. Migration may start as early as late August in the most easterly and northerly parts of the range, but the majority of birds, with shorter distances to cover, head south from September to mid-December. However, hard weather may force further movement. Return migration varies between mid-February around the Mediterranean to May in northern Sweden and central Siberia. Vagrants have been recorded in Greenland, various Atlantic islands, and West Africa.
Breeding and survivalEdit
The female Song Thrush builds a neat cup-shaped nest lined with mud and dry grass in a bush, tree or creeper, or, in the case of the Hebridean subspecies, on the ground. She lays four or five bright glossy blue eggs which are lightly spotted with black or purple; they are typically 2.7 x 2.0 centimetres (0.79 x 1.06 in) in size and weigh 6.0 grammes (0.21 oz), of which 6% is shell. The female incubates the eggs alone for 10–17 days, and after hatching a similar time elapses until the young fledge. Two or three broods in a year is normal, although only one may be raised in the north of the range. On average, 54.6% of British juveniles survive the first year of life, and the adult annual survival rate is 62.2%. The typical lifespan is three years, but the maximum recorded age is 10 years 8 months.
The Song Thrush is occasionally a host of parasitic cuckoos, such as the Common Cuckoo, but this is very rare because the thrush recognizes the cuckoo's non-mimetic eggs. However, the Song Thrush does not demonstrate the same aggression toward the adult Cuckoo that is shown by the Blackbird. The introduced birds in New Zealand, where the cuckoo does not occur, have, over the past 130 years, retained the ability to recognise and reject non-mimetic eggs.
Adult birds may be killed by cats, Little Owls and Sparrowhawks, and eggs and nestlings are taken by Magpies, Jays, and, where present, Grey Squirrels. As with other passerine birds, parasites are common, and include endoparasites, such as the nematode Splendidofilaria (Avifilaria) mavis whose specific name mavis derives from this thrush. A Russian study of blood parasites showed that all the Fieldfares, Redwings and Song Thrushes sampled carried haematozoans, particularly Haemoproteus and Trypanosoma. Ixodes ticks are also common, and can carry pathogens, including tick-borne encephalitis in forested areas of central and eastern Europe and Russia, and, more widely, Borrelia bacteria. Some species of Borrelia cause Lyme disease, and ground-feeding birds like the Song Thrush may act as a reservoir for the disease.
The Song Thrush is omnivorous, eating a wide range of invertebrates, especially earthworms and snails, as well as soft fruit and berries. Like its relative, the Blackbird, the Song Thrush finds animal prey by sight, has a run-and-stop hunting technique on open ground, and will rummage through leaf-litter seeking potential food items.
Snails are especially important when drought or hard weather makes it difficult to find other food. The thrush often uses a favourite stone as an "anvil" on which to smash the snail before extracting the soft body and invariably wiping it on the ground before consumption. Young birds initially flick objects and attempt to play with them until they learn to use anvils as tools to smash snails. The nestlings are mainly fed on animal food such as worms, slugs, snails and insect larvae.
The Grove Snail (Cepaea nemoralis) is regularly eaten by the Song Thrush, and its polymorphic shell patterns have been suggested as evolutionary responses to reduce predation; however, Song Thrushes may not be the only selective force involved.