THE SPINE-TAILED SWIFT.
By V. R. Balfour-Browne.
Swifts are perhaps the most powerfully winged, in proportion to their weight, of all British birds. Their form is that which has been found to make the fastest sailing vessel—full forwards and lengthened, and tapering backwards. The difficulty in regard to these birds, and particularly in regard to the Alpine swift and the spine-tailed swift, is to obtain the necessary opportunities and conditions for comparing their maximum speed with that of other very fast birds. It is difficult to realise merely from a consideration of the description and measurements of these three swifts in the authoritative works of ornithologists how much larger the Alpine swift and spine-tailed swift are than the common swift. I have had opportunities of handling and examining the stuffed specimens of these birds in the British Museum (Natural History) at South Kensington, and should like to acknowledge here the courtesy and assistance given to me at the Museum by Mr. W. P. Pycraft, Dr. P. R. Lowe, and Mr. N. B. Kinnear.
The actual measurements of the three birds are as follows:
| Length. | Wing. | |||
| Common Swift | 6·75 | inches | 6·8 | inches |
| Alpine Swift | 8 | ” | 8·45 | ” |
| Needle-tailed Swift | 8 | ” | 8·1 | ” |
It is not generally realised that the common swift, so well known in this country, which looks so imposing in flight as it glides overhead with wings extended, is hardly so large, when plucked, as a man’s thumb-joint and weighs slightly over half an ounce.
Bearing in mind that as between two birds of the same build and structure the larger will, when it gets going, fly faster than the smaller one, it would naturally be expected, as is the undoubted fact, that the Alpine swift and spine-tailed swift are faster fliers than the common swift.
The falconer has in the case of the swift very little opportunity of comparing its speed with that of the peregrine. This is partly because the peregrine, whether it be the falcon (the female bird) or the tiercel (the male bird), will probably not attempt to kill the swift, it being too small a prey. There is the further difficulty that the swift rarely continues on a level flight.