Swallows, martins, and saw-wings, belonging to the family Hirundinidae, are passerine songbirds found globally, including occasionally in Antarctica. Highly adapted for aerial feeding, they have a distinctive appearance. Around 90 species are recognized, with the greatest diversity in Africa, where they are believed to have evolved as hole-nesters.
This family consists of two subfamilies: Pseudochelidoninae (river martins) and Hirundininae (all other swallows and martins). In the Old World, “martin” refers to squarer-tailed species, while “swallow” is used for fork-tailed species.
Swallows are characterized by their slender bodies, long wings, and short bills with strong jaws. They have excellent vision due to two foveae in each eye and can spot prey effectively. Their size ranges from 10–24 cm in length and 10–60 g in weight. Tail length varies, with males typically having longer tails to attract females.
Their legs are short and adapted for perching rather than walking, giving them a shuffling gait. Common plumage features glossy dark blue or green atop and plain or streaked underparts. Chicks hatch naked and with closed eyes, and fledglings resemble duller adults.
Swallows have a cosmopolitan distribution, breeding on every continent except Antarctica. Notable species include the Pacific swallow, found on Pacific islands, and the Mascarene martin from Reunion and Mauritius. Many species, like the barn swallow, have extensive ranges, breeding in the Northern Hemisphere and wintering in the Southern Hemisphere, while others, like the lesser striped swallow, are partial migrants within Africa.
Swallows thrive in diverse habitats, relying on flying insects found near waterways, grasslands, woodlands, and urban areas. Changes in land use have allowed species like the welcome swallow to expand their ranges, colonizing regions like New Zealand. Temperate species migrate in winter, while tropical species are often more sedentary, with some making short migrations.
Historically, swallows were believed to hibernate, a notion supported by their behavior of roosting in groups during harsh weather. They are skilled flyers, with males selecting nest sites and attracting females through song and display. Some species are territorial, while others may gather in large flocks to roost, providing safety from predators. In communal nesting species, males may defend territory, while colonial species mob threats to their nests.
Swallows are primarily insectivorous, catching flying insects in mid-air, with their diet varying by species and season. They tend to be selective, often opting for larger prey, and avoid stinging insects like bees and wasps. Some species also consume fruits and seeds, particularly in Africa.
Swallows forage primarily while flying, using different techniques based on prey mobility. When feeding together, different species occupy various heights, leading to niche separation.
Nesting habits vary. More primitive swallows use existing cavities, while others excavate burrows. Mud-nesting species, common in the Old World, build nests from mud, while cavity-nesting species are prevalent in the New World. Many swallows nest in colonies, benefiting from improved breeding sites due to man-made structures but facing challenges like ectoparasites.
Mated pairs are monogamous, with nonmigratory species often remaining near their breeding area year-round. Migratory swallows may return to the same nesting sites. Breeding is seasonal for temperate species, while subtropical and tropical species may be either continuous or seasonal, often aligning with insect activity peaks. All swallows are protective of their nests, and males contribute significantly to parental care.
