Description
The swallows and martins have an evolutionary conservative body shape which is similar across the clade but is unlike that of other passerines. 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. Swallows usually forage at around 30–40 km/h, although they are capable of reaching speeds of between 50–65 km/h when traveling.
Like the unrelated swifts and nightjars, which hunt in a similar way, they have short bills, but strong jaws and a wide gape. Their body length ranges from about 10–24 cm (3.9–9.4 in) and their weight from about 10–60 g (0.35–2.1 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. In Barn Swallows the tail of the male is 18% longer than the females, and females will select mates on the basis of tail length.
The legs are short, and their feet are adapted for perching rather than 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 gait. The leg muscles of the river martins (Pseudochelidon) are stronger and more robust than those of other swallows.
The most common hirundine plumage is glossy dark blue or green above and plain or streaked underparts, often white or rufous. Species which burrow or live in dry or mountainous areas are often matte brown above (e.g. Sand Martin and Crag Martin). The sexes show limited or no sexual dimorphism, with longer outer tail feathers in the adult male probably being the most common distinction.
The chicks hatch naked and with closed eyes. Fledged juveniles usually appear as duller versions of the adult.
Read more about this topic: Hirundinidae
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