It may be the season to notice these birds as they wheel and scream around buildings in the evening and give one of the sounds of summer. Although here today, they may be gone tomorrow, if we get more chilly nights, for they leave earlier than any other ‘guest of summer’.*

It [the swift] leaves early, from August onwards, in order to avoid even the earliest intimations of winter. —Matthieu Ricard, The Mystery of Animal Migration,Constable & Co Ltd, 1969.

Last week a well-known author was chided for referring to swifts, in an article, as hirundines: and indeed they belong to a different family called Apodidae (‘having no feet’), although that is not quite the case: their legs and feet are basic, and they hardly use them.

The discovery that they are of a family different from swallows and martins (Hirundidae) belongs to the 20th century. Even the Cambridge scholars Willughby and Ray, who made the first classification of birds in their Ornithologia (1676)** did not make this distinction.

The similarity in shape seems just a matter of aerodynamic evolution; and swifts are among the speediest of flyers, for whom 70 mph is commonplace.

Pliny the Elder, not surprisingly, does not make any such fine distinctions in his tenth book, in which he deals with natura avium. But it is interesting to read his description of how such birds migrate, and of migration in general, with surprisingly accurate information confirmed by modern science. The tenth book, like so many of the others, is a mixture of fact, legend, hearsay and folk tale: common sense and fiction lie side by side.

*Shakespeare, Macbeth, Act I, Scene 6 (viewing recommended).

**Later modified by Linnaeus.