[4] This is a large swift measuring 20–22 cm in length[5] with a wingspan of 54–60 cm with broad wings and tail with a shallow fork,[4] superficially similar to a large barn swallow or house martin although unrelated to these two species, since swifts are in the order Apodiformes.

Upper parts are olive-brown with sharp and long wings with wing-tips appearing blacker; underparts with white throat (often not easily visible)[5] and highly visible and distinctive oval white belly patch encircled by olive-brown breastband, flanks and undertail-coverts.

The species seems to have been much more widespread during the last ice age, with a large colony breeding, for example in the Late Pleistocene Cave No 16, Bulgaria, around 18,000–40,000 years ago.

Young swifts in the nest can drop their body temperature and become torpid if bad weather prevents their parents from catching insects nearby.

They have adapted well to urban conditions, frequently nesting in old buildings in towns around the Mediterranean, where large, low-flying flocks are a familiar feature there in summer.

Alpine swifts have a short forked tail and very long swept-back wings that resemble a crescent or a boomerang but may (as in the image) be held stretched straight out.

In 2011, Felix Liechti and his colleagues at the Swiss Ornithological Institute attached electronic tags that log movement to six alpine swifts and it was discovered that the birds could stay aloft in the air for more than 200 days straight.

Insects across 10 orders and 79 families were documented in the diets of individuals from Africa and Europe, with the homoptera, diptera and hymenoptera being the most often consumed.