and some occasionally to the beginning of November. This early retreat is mysterious and wonderful, since that time is often the sweetest season in the year. But what is more extraordinary, they begin to retire still earlier in the most southerly parts of Andalusia, where they can be in no ways influenced by any defect of heat; or, as one might suppose, failure of food. Are they regulated in their motions with us by a defect of food, or by a propensity to moulting, or by a disposition to rest after so rapid a life, or by what? This is one of those incidents in natural history that not only baffles our searches, but almost eludes our guesses!
These hirundines never perch on trees or roofs, and so never congregate with their congeners. They are fearless while haunting their nesting-places, and are not to be scared with a gun; and are often beaten down with poles and cudgels as they stoop to go under the eaves. Swifts are much infested with those pests to the genus called hippoboscæ hirundinis; and often wriggle and scratch themselves in their flight to get rid of that clinging annoyance.
Swifts are no songsters, and have only one harsh screaming note; yet there are ears to which it is not displeasing, from an agreeable association of ideas, since that note never occurs but in the most lovely summer weather.
They never can settle on the ground but through accident; and when down, can hardly rise, on account of the shortness of their legs and the length of their wings; neither can they walk, but only crawl; but they have a strong grasp with their feet, by which they cling to walls. Their bodies being flat they can enter a very narrow crevice; and where they cannot pass on their bellies they will turn up edgewise.
The particular formation of the foot discriminates the swift from all the British hirundines; and indeed from all other known birds, the hirundo melba, or great white-bellied swift of Gibraltar, excepted; for it is so disposed as to carry "omnes quatuor digitos anticos" all its four toes forward; besides, the least toe, which should be the back toe, consists of one bone alone, and the other three only of two apiece, a construction most rare and peculiar,
