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.
“Besides its swiftness,” he writes, “it is almost tireless of wing, being second only in that respect to the frigate bird, the bird of eternal flight. Both have very long wings in relation to the body--an indication of rapid flight. The swift, a bird of passage which crossed the wide sea after breeding in Japan, is not known to alight in Australia, where it spends a considerable time hunting its insect prey in the upper air.”
In _A History of the Birds of Europe_,[23] Dresser writes: “The present species (_Acanthyllis caudacuta_ or _Chaetura caudacuta caudacuta_) and _Acanthyllis gigantea_ are said to be the swiftest birds in existence. Tickell says that he never witnessed anything equal to the prodigious swiftness of its movements.”
_Chaetura caudacuta cochinchinensis_ (which is to be found in Malacca, Sumatra, and Cochin China) is a form of the spine-tailed swift allied to that species (_Chaetura caudacuta caudacuta_) which is so rare a visitor here. I have examined and compared numerous specimens of these three species of spine-tailed swifts, and it would seem practically certain, in view of their similarity in size and structure, that their speed must be similar.
Mr. E. Stuart Baker, who has made experiments as to the speed of the _Chaetura nudipes_ and the _Chaetura cochinchinensis_, writes:[24] “Both these species have a normal flighting speed of something very nearly approaching 200 miles an hour, enormously in excess of the powers of any other bird with which I am acquainted. In North Cachar, Assam, these birds used to fly directly over my bungalow in Haflang, flying thence in a straight line to a ridge of hills exactly two miles away, and when over the ridge at once dipping out of sight. We constantly timed these swifts and found that stop-watches made them cover this distance in from 36 seconds to 42 seconds, _i.e._ at a rate of exactly 200 miles an hour to 171·4.”