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“DRUMMING” BY SWIFTS
Author(s) -
Bednall D. K.
Publication year - 1963
Publication title -
ibis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 80
eISSN - 1474-919X
pISSN - 0019-1019
DOI - 10.1111/j.1474-919x.1963.tb01593.x
Subject(s) - feather , wing , geography , wife , zoology , physics , biology , law , political science , thermodynamics
On 27 April 1958, while my wife and I were watching a party of 20–30 Mottled Swifts Apus aequatorialis over a dam ten miles west of Nairobi, Kenya, we repeatedly heard quite a loud “prrrpt‐prrrpt‐prrrpt”. We discovered that the swifts were making this noise by spreading and slightly depressing their tails and moving them sideways so that the outer feather was almost parallel with the wing. The ‘leading’ feather thus projected into the slipstream was quite clearly seen to vibrate at the same time as the noise was heard. We watched this performance for about half an hour and noted that the tails were invariably turned to the right; we were both using binoculars. We saw that several birds were performing in this manner but it did not appear to be in connection with any display towards any other particular member of the party. The sexes of the Mottled Swift are indistinguishable in the field. The ‘drumming’ took place in the early part of the dive towards the surface of the dam from which the birds were drinking on the wing; it did not appear to cause any deflection of the flight path.