Belonging to the bird family Hirundininae, swallows are usually distinguished from their genus-mates the square-tailed martins by virtue of their forked tails. Breeding on practically every continent save for Antarctica, the swallow population is comprised of several species all over the world, each with their own distinctive characteristic sizes.
The Tree Swallow, which breeds in North America and migrates to Central America, Mexico and the Caribbean during the winter, has an average length of 13.5 cm (5 inches) and weighs approximately 20 grams. Breeding in coastal regions ranging from Mexico, Central America and up to Panama, the Mangrove Swallow has a common size of 13 cm (5 inches) and weighs in at roughly 14 grams. The White-winged Swallow of tropical South America has a length of 13.2 cm and weighs in at 17 grams. Endemic to Chile, Argentina and the Falkland Islands, the Chilean Swallow is 11-13 cm (4.5-5 inches) long. The Blue-and-White Swallow, which breeds from Nicaragua to South America, has an average length of 11-12 cm and weighs around 10 grams. The Northern Rough-winged Swallow, which migrate to the US Gulf coast and southward to Central America, mature to a length of 13-15 cm. The Southern Rough-winged Swallow of Central and South America grow to a length of 13.5 cm and a weight of 15 grams.
The most widespread swallow species in the world, found in Asia, Africa, Europe and America, the Barn Swallow has a length of 17-19 cm (6.7-7.5 inches) which includes its 2-7 cm (0.8-2.8 inches) outer tail feathers. It also has a 32-34.5 cm (12.6-13.6 inch) wingspan and a weight of 16-22 grams (0.56-0.78 oz). The Pacific Swallow of tropical south Asia, also known as the Hill Swallow, is a very small size of 13 cm. The Welcome Swallow indigenous to Australia and New Zealand has a length of 15 cm. The White-throated Swallow of southern Africa is 14-17 cm in length. The Wire-tailed Swallow, which breeds in Africa and the tropics of southern Asia, is only 14 cm long. Another South African species, the Pearl-breasted Swallow, is 13-14 cm in length. The Blue Swallow, also of southern Africa, is 18-25 cm long.
Breeding in southern Africa, the Greater Striped Swallow has a length of 18-20 cm. Smaller is the Lesser Striped Swallow of sub-Saharan Africa, with a length of 15-10 cm. Another sub-Saharan breed, the Mosque Swallow, is sized at 25 cm. The Rufous-chested Swallow of equatorial Africa measures 24 cm in length. The Striated Swallow from South to Southeast Asia is at a length of 19 cm. The Cliff Swallow of North America has an average size of 13 cm (5 inches), while its relative, the Cave Swallow endemic to Mexico and the Greater Antilles, is 12-14 cm long and weighs an average of 19 grams.
Some consider swallows as pests because of the damage they cause when they make their mud nests on the walls of houses and buildings. But these birds are also useful for pest control as they commonly prey on insects. Nonetheless, swallows of every size and specie can be spotted flying in almost every sector of the globe, one of the most prevalent bird families in the entire world.