Hirundinidae – Swallows & Martins

Hirundinidae (Swallows, Saw-wings & Martins) are a family of passerines, which are characterised by their adaptation to aerial feeding. Swallow is used colloquially in Europe as a synonym for the Barn Swallow.

This family comprises two subfamilies: Pseudochelidoninae (the river martins of the genus Pseudochelidon) and Hirundininae (all other swallows and martins). Within the Hirundininae, the name ‘martin’ tends to be used for the squarer-tailed species, and the name ‘swallow’ for the more fork-tailed species; however, there is no scientific distinction between these two groups. The family contains around ninety-two species in twenty-one genera.

The hirundines have an evolutionary conservative body shape, which is unlike that of any other passerines. They have adapted to hunting insects on the wing by developing a slender, streamlined body and long pointed wings, which allow for great manoeuvrability and endurance, as well as frequent periods of gliding. Because their body shape allows for a very efficient flight, their metabolic rate during flight is up to 72% lower than similar sized passerines. They have particularly sharp lateral and frontal vision which helps them to track prey. They also have relatively long eyes and their length almost equals their width. These long eyes allow for an increase in visual acuity without competing with the brain for space inside the head. In fact, the morphology of their eyes is very similar to that of raptors.

Pacific Swallow Hirundo javanica- ©Nick Green Bird-Photo-Tours ASIA

Like the unrelated swifts and nightjars which hunt in a similar way, they have short beaks but strong jaws and a wide gape. Across the family their body length ranges from about 10 to 24 cm and their weight from about 10 to 60 g. The smallest species by weight may be the Fanti Sawing at a mean body mass of just 9.4 g while the Purple Martin and Southern Martin, which both weigh in excess of 50 g, rival one another as the heaviest swallows. Their wings are long, pointed, and have nine primary feathers. The tail has twelve feathers and maybe deeply forked, somewhat indented or square-ended. A long tail increases manoeuvrability; it may also function as a sexual adornment, since the tail is frequently longer in males. In Barn Swallows, the tail of the male is 18% longer than those of the female, and female select mates on the basis of tail length. Her feet on the other hand are short and adapted for perching while the walking, as the front toes are partially joined at the base. Swallows are capable of walking and even running, but they do so with a shuffling waddling gate. The leg muscles of river martins are stronger and more robust than those of other swallows. They have other characteristics that separate them from the rest of the family too. The structure of the syrinx is substantially different between the two sub-families and in most swallows, the bill, legs and feet are dark brown or black. But in the river martins, the bill is orange-red and their legs and feet are pink.

The most common plumage across the family is glossy dark blue or green above and plain or streaked underneath often white or slightly rufous. Species that burrow or live in dry or mountainous areas however, often are matt brown above, such as Sand Martins and Crag Martins. They show limited or no sexual dimorphism, with longer male tail feathers probably being the most common distinction. Chicks hatch naked with closed eyes. Fledged juveniles usually appear as duller versions of the adults.

Barn Swallow Hirundo rustica – ©Nick Green Bird-Photo-Tours ASIA

The swallows have a cosmopolitan distribution across the world and breed on all the continents except Antarctica. They’re also a number which occur on oceanic Islands. It is believed that this family originated in Africa as hole-nesters; Africa still has the greatest diversity of species. A number of European and North American species are long-distance migrants; by contrast, the West and South African swallows are non-migratory. Many species have enormous worldwide arranges, particularly the Barn Swallow, which breeds over most of the northern hemisphere and winter is over most of the southern hemisphere. They occupy a wide range of habitats. Because they are dependent on flying insects they are commonly seen over waterways and lakes and frequently feed over these, but they can be found in open habitat including grasslands, open woodland, savanna, marshes, mangroves and scrubland, from sea level to high alpine areas. Many species inhabit human-altered landscapes, including agricultural land and even urban areas. In fact, land use changes has, in some cases, caused some species to expand their range, most impressively the Welcome Swallow, which began to colonise New Zealand in the 1920s, started breeding in the 1950s and is now a common landbird there.

Lesser Striped Swallow Cecropis abyssinica – ©Dubi Shapiro

In temperate regions, species that breed in the summer usually migrate during the winter because of the collapse of insect populations during that season. However, species that are native to more tropical areas, either do not migrate at all, or make shorter migrations. During the winter Emma greeting swallows can form enormous roosts. For example, one winter roosting sight in Nigeria has attracted 1 ½ million individuals. Most species, most of the time are completely insectivorous. However, some birds have been observed heating fruit and even the seeds of acacia trees.

A large number of species nest in holes sometimes in sandbanks, old woodpecker nests or other existing cabbages. Those nesting in sandbanks excavate Burrows in the soft substrate.

Purple Martin Progne subis – ©Dubi Shapiro

Other species, particularly some of the Martens, build mad nests using an overhead to shelter in locations that are protected from both weather and predators. Mud nesting is the most common in the old world, particularly Africa. Pairs tend to be monogamous and pairs of non-migratory species often stay near their breeding area. Migratory species often return to the same breeding area year after year and may select the same nest site if they were previously successful in that location. First year breeders, generally select a nesting site close to where they were raised.

A few species of swallow and martin are threatened with extinction by human activities, although other species have benefited from human changes to the environment and live around humans.