Balestruccio

Identificazione

The adult western house martin is 13 cm (5 in) long, with a wingspan of .mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}26–29 cm (10–11+1⁄2 in) and a weight averaging 18.3 g (21⁄32 oz). It is steel-blue above with a white rump, and white underparts, including the underwings; even its short legs have white downy feathering. It has brown eyes and a small black bill, and its toes and exposed parts of the legs are pink. The sexes are similar, but the juvenile bird is sooty black, and some of its wing coverts and quills have white tips and edgings. D. u. lagopodum differs from the nominate race in that its white rump extends much further onto the tail, and the fork of its tail is intermediate in depth between that of D. u. urbicum and that of the Asian house martin.<p>The white rump and underparts of the western house martin, very noticeable in flight, prevent confusion with other widespread Palaeoarctic swallows such as the barn swallow (Hirundo rustica), sand martin (Riparia riparia) or red-rumped swallow (Cecropis daurica). In Africa, confusion with grey-rumped swallow (Pseudhirundo griseopyga) is possible, but that species has a grey rump, off-white underparts and long, deeply forked tail. The western house martin flies with a wing beat averaging 5.3 beats per second, which is faster than the wing beat of 4.4 beats per second for the barn swallow, but the flight speed of 11 m/s (36 ft/s) is typical for hirundines.<p>The western house martin is a noisy species, especially at its breeding colonies. The male's song, given throughout the year, is a soft twitter of melodious chirps. The contact call, also given on the wintering grounds, is a hard chirrrp, and the alarm is a shrill tseep.

Tassonomia

The western house martin was first described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae as Hirundo urbica, but was placed in its current genus, Delichon, by Thomas Horsfield and Frederic Moore in 1854. Delichon is an anagram of the ancient Greek term χελιδών (chelīdōn), meaning "swallow", and the species name urbicum (urbica until 2004, due to a misunderstanding of Latin grammar) means "of the town" in Latin.<p>The genus Delichon is a recent divergence from the barn swallow genus Hirundo, and its three members are similar in appearance with blue upperparts, a contrasting white-rump, and whitish underparts. In the past, the western house martin was sometimes considered to be conspecific with the Asian house martin (D. dasypus), which breeds in the mountains of central and eastern Asia and winters in Southeast Asia, and it also closely resembles the Nepal house martin (D. nipalense), a resident in the mountains of southern Asia. Although the three Delichon martins are similar in appearance, only D. urbicum has a pure white rump and underparts.<p>The western house martin was formerly considered to be conspecific with the Siberian house martin (Delichon lagopodum) that breeds eastwards of the Yenisei to Kolyma and south to northern Mongolia and northern China; it winters in southern China and Southeast Asia. The two species were split based on morphological and vocal differences. Other races, like meridionalis from around the Mediterranean have been described, but the claimed differences from the nominate race are clinal, and therefore probably invalid.

Nome scientifico

Delichon urbicum

Autorità

(Linnaeus, 1758)

Ordine

Passeriformi

Famiglia

Hirundinidae

Genere

Delichon

Areale e habitat

The western house martin breeds across temperate Eurosiberia east to central Mongolia and the Yenisei River, and in Morocco, Tunisia and northern Algeria, and migrates on a broad front to winter in sub-Saharan Africa.<p>The preferred habitat of the western house martin is open country with low vegetation, such as pasture, meadows and farmland, and preferably near water, although it is also found in mountains up to at least 2,200 m (7,200 ft) elevation. It is much more urban than the barn swallow, and will nest even in city centres if the air is clean enough. It is more likely to be found near trees than other Eurasian swallows, since they provide insect food and also roosting sites. This species does not normally use the reed-bed roosts favoured by migrating barn swallows.<p>It uses similar open habitats on the wintering grounds, but the western house martin is less conspicuous than wintering barn swallows, tending to fly higher and be more nomadic. In the tropical parts of its wintering range, like East Africa, it appears to be mainly found in the higher areas.<p>The western house martin is a migrant which moves on a broad front (i.e., European birds are not funnelled through the short sea crossings used by large soaring birds, but cross the Mediterranean and Sahara). While migrating they feed in the air on insects, and they usually travel in daylight. Migration brings its own hazards; in 1974, several hundred thousand birds of this species were found dead or dying in the Swiss Alps and surrounding areas, caught by heavy snowfall and low temperatures. Adult survival on autumn migration depends mainly on temperature, with precipitation another major factor, but for juveniles low temperatures during the breeding season are more critical. It is anticipated that since extreme weather is predicted to become more frequent with climate change, future survival rates will depend more on adverse weather conditions than at present.<p>The western house martin returns to the breeding grounds a few days after the first barn swallows; and like that species, particularly when the weather is poor, it seldom goes straight to the nesting sites, but hunts for food over large fresh water bodies. There are records of migrant house martins staying to breed in Namibia and South Africa instead of returning north. As would be expected for a long-distance migrant, it has occurred as a vagrant eastwards to Alaska and west to Newfoundland, Bermuda and the Azores.

Areale riproduttivo

Paleartico: ampiamente distribuito

Areale non riproduttivo

sw Asia and AF

Migrazione

Migratori completi

Comportamento

Comportamento migratorio: Migratori completi.

Conservazione

Tendenza della popolazione: in diminuzione.

Tendenza della popolazione

in diminuzione