Swallow

The swallows and martins are a group of passerine birds in the family Hirundinidae which are characterised by their adaptation to aerial feeding. Swallow is used colloquially in Europe as a synonym for the barn swallow.The entire family contains around 83 species in 19 genera.The swallows have a cosmopolitan distribution across the world and breed on all the continents except Antarctica. It is believed that this family originated in Africa as hole-nesters; Africa still has the greatest diversity of species.They also occur on a number of oceanic islands. A number of European and North American species are long-distance migrants; by contrast, the West and South African swallows are non-migratory.The swallows and martins have an evolutionarily conservative body shape which is similar across the clade but is unlike that of otherpasserines. Swallows have adapted to hunting insects on the wing by developing a slender, streamlined body and long pointed wings, which allow great maneuverability and endurance, as well as frequent periods of gliding. 

Their body shape allows for very efficient flight, which costs 50–75% less for swallows than equivalent passerines of the same size.Their body length ranges from about 10–24 cm (3.9–9.4 in) and their weight from about 10–60 g (0.35–2.12 oz). The wings are long, pointed, and have nine primary feathers. The tail has 12 feathers and may be deeply forked, somewhat indented, or square-ended. A long tail increases maneuverability, and may also function as a sexual adornment, since the tail is frequently longer in males.For the most part swallows are insectivorous, taking flying insects on the wing. Across the whole family a wide range of insects are taken from most insect groups, but the composition of any one prey type in the diet varies by species and with the time of year. Individual species may be selective, they do not scoop up every insect around them, but instead select larger prey items than would be expected by random sampling.

The more primitive species nest in existing cavities, for example in an old woodpecker nest, while other species excavate burrows in soft substrate such as sand banks. Swallows in the genera Hirundo, Ptyonoproggne, Cecropis, Petrochelidon and Delichon build mud nests close to overhead shelter in locations that are protected from both the weather and predators. The mud-nesters are most common in theOld World, particularly Africa, whereas cavity-nesters are the rule in the New World. Mud nesting species in particular are limited in areas of high humidity, which causes the mud nests to crumble. Many cave, bank and cliff dwelling species of swallow nest in large colonies. Mud nests are constructed by both males and females, and amongst the tunnel diggers the excavation duties are shared as well. Inhistorical times, the introduction of man-made stone structures such as barns and bridges, together with forest clearance, has led to an abundance of colony sites around the globe, significantly increasing the breeding ranges of some species. Birds living in large colonies typically have to contend with both ectoparasites and conspecific nest parasitism.Old males benefit most from coloniality, since they are able to maintain their own nests and benefit from frequent extra-pair copulations.