The Common House Martin (Delichon urbicum), is a migratory passerine bird of the swallow family which breeds in Europe, north Africa and temperate Asia; and winters in sub-Saharan Africa and tropical Asia. It feeds on insects which are caught in flight, and it migrates to climates where flying insects are plentiful. It has a blue head and upperparts, white rump and pure white underparts, and is found in both open country and near human habitation.
Both the scientific and colloquial name of the bird are related to its use of man-made structures. It builds a closed cup nest from mud pellets under eaves or similar locations on buildings usually in colonies, but sometimes fouling below nests can be a problem.
It is hunted by the Hobby (Falco subbuteo), and like other birds is affected by internal parasites and external fleas and mites, but its large range and population mean that it is not threatened globally.
Distribution and habitatEdit
The preferred habitat of the Common 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 metres (7,200 ft) altitude. 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 swallows, since they provide insect food and also roosting sites. This species does not normally use the reed-bed roosts favoured by migrating Swallows.
It uses similar open habitats on the wintering grounds, but the Common House Martin is less conspicuous than wintering Swallows, tending to fly higher and be more nomadic. In the tropical parts of its wintering range, like East Africa and Thailand, it appears to be mainly found in the higher areas.
The Common 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 generally travel in daylight, although some birds may move at night. 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.
The Common House Martin returns to the breeding grounds a few days after the first Swallows; 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.
The adult Common House Martin of the western nominate race is 13 centimetres (5.1 in) long, with a wing span of 26–29 centimetres (10.2–11.4 in) and a weight averaging 18.3 grammes (0.65 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.
The white rump and underparts of the Common House Martin, very noticeable in flight, prevent confusion with other widespread Palaeoarctic swallows such as the Swallow (Hirundo rustica) & Sand Martin (Riparia riparia). The Common 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 Swallow.
The Common 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.
The Common House Martin was originally a cliff and cave nester, and some cliff-nesting colonies still exist, with the nests built below an overhanging rock. It now largely uses human structures such as bridges and houses. Unlike the Swallow, it uses the outside of inhabited buildings, rather than the inside of barns or stables. The nests are built at the junction of a vertical surface and an overhang, such as on house eaves, so that they may be strengthened by attachment to both planes.
Breeding birds return to Europe between April and May, and nest building starts between late March in North Africa and mid-June in Lapland. The nest is a neat closed convex cup fixed below a suitable ledge, with a narrow opening at the top. It is constructed by both sexes with mud pellets collected in their beaks, and lined with grasses, hair or other soft materials. The mud, added in successive layers, is collected from ponds, streams or puddles. House Sparrows frequently attempt take over the nest during construction, with the House Martins rebuilding elsewhere if they are successful. The entrance at the top of the cup is so small that the sparrows cannot take over the nest once it is complete.
The Common House Martin tends to breed colonially, and nests may be built in contact with each other. A colony size of less than 10 nests is typical, but there are records of colonies with thousands of nests. Four or five white eggs are usually laid, which average 1.9 x 1.33 centimetres (0.75 x 0.52 in) in size, and weigh 1.7 grammes (0.06 oz). The female does most of the incubation, which normally lasts 14–16 days. The newly hatched chicks are altricial, and after a further 22–32 days, depending on weather, the chicks leave the nest. The fledged young stay with, and are fed by, the parents for about a week after leaving the nest. Occasionally, first-year birds from the first brood will assist in feeding the second brood.
There are normally two broods each year, the nest being reused for the second brood, and repaired and used again in subsequent years. Hatching success is 90%, and fledging survival 60–80%. Average mortality for the adult is 40–70%. Third broods are not uncommon, though late nestlings are often left to starve. Although individuals aged 10 and 14 years have been recorded, most survive less than five years. For weeks after leaving the nest the young congregate in ever-increasing flocks which, as the season advances, may be seen gathering in trees or on housetops, or on the wires with Swallows. By the end of October, most Martins have left their breeding areas in western and central Europe, though late birds in November and December are not uncommon, and further south migration finishes later anyway.
Once established, pairs remain together to breed for life; however, extra-pair copulations are common, making this species genetically polygamous, despite being socially monogamous. A Scottish study showed that 15% of nestlings were not related to their putative fathers, and 32% of broods contained at least one extra-pair chick. Extra-pair males, usually from nests where laying had already taken place, were often seen to enter other nests. The paired male initially ensured that his female spent little time alone at the nest, and accompanied her on flights, but the mate-guarding slackened after egg laying began, so the youngest nestling was the most likely to have a different father.
The Common House Martin is similar in habits to other aerial insectivores, including other swallows and martins and the unrelated swifts, and catches insects in flight. In the breeding areas, flies and aphids make up much of the diet, and in Europe, the House Martin takes a larger proportion of aphids and small flies than the Swallow. As with that species, Hymenoptera, especially flying ants, are important food items in the wintering area.
This species hunts at an average height of 21 metres (70 ft) during the breeding season, but lower in wet conditions. The hunting grounds are typically within 450 metres (1,500 ft) of the nest, with a preference for open ground or water, the latter especially in poor weather, but the martins will also follow the plough or large animals to catch disturbed insects. On the wintering grounds, hunting takes place at a greater height of over 50 metres (165 ft).