In the tables given above[16] Colonel Meinertzhagen estimates the speed of the normal and migratory rate of flight of falcons at 40 to 48 miles an hour, whilst Captain Portal estimates the maximum speed of the peregrine falcon in level flight through still air at 62 miles an hour. Captain Portal adds that the speed given is for a good trained bird, and that a wild bird is faster. In view of Colonel Meinertzhagen’s observations from his aeroplane and the figures given above, it would appear to be certain that the Alpine swift is faster than the peregrine falcon in horizontal flight. We have now to consider the speed of the spine-tailed or needle-tailed swift. There seems to be no doubt that this bird is a much faster flier than the Alpine swift, though at first sight and without a careful examination of the skeletons, it is difficult to state why this should be so. I have compared various specimens of the two birds, and there appears to be little difference in their size. Colonel Meinertzhagen, who has been so kind as to discuss the subject with me, agrees that the spine-tailed swift is the faster flier, and tells me that he thinks it is probably the heavier bird of the two, and that this may account for its greater rapidity of flight. The wing of the Alpine swift is 8·45 inches, that of the spine-tailed swift is 8·1 inches. The length of both birds is 8 inches,[17] although Dresser[18] gives the total length as 8·5 and that of the spine-tailed swift as 8·1 inches. The genus _Chaetura_, to which the needle-tailed swift belongs, is easily distinguishable from the genus _Apus_ (to which the common swift and Alpine swift belong) by the wedge-shaped tail in which the shafts of the feathers are longer than the webs and protrude like spines. The tail in the only species (_Chaetura caudacuta caudacuta_) occurring in the British Isles, compared with that of the Alpine swift, is very short. It is almost square, and has ten feathers, which are very stiff and the shafts of which project 4-6 mm. (·156-·234 inch) beyond the web in a stiff point like that of a needle or spine.[19] The shafts of the primaries are very strong and the wings very long. Gould[20] says, in reference to the spine-tailed swift, in a passage which is quoted in Seebohm:[21] “The keel or breast bone of this species is more than ordinarily deep and the pectoral muscles more developed than in any of its weight with which I am acquainted.” Probably the last-mentioned facts largely account for its superiority in speed over the Alpine swift. In an article entitled “The Twelve Swiftest Birds of Australia,”[22] in which Mr. E. S. Sovenson gives the views of himself and various friends of his as to the relative speed of Australian birds, he says that after long observation he and they have no hesitation in stating that the spine-tailed swift is the swiftest Australian bird, and states that its speed has been computed at 180 miles an hour.