Two large ticks (Anapera fimbriata) are usually found on this bird, similar to Anapera pallida of C. apus.
For a fuller account, see A. Newton, Dict. Birds, 1893, pp. 440-451.
These are produced by the prismatic surfaces of the feathers, cf. pp. [3], [4].
Ibis, 1859, pp. 139, 140.
Zool. Voy. Beagle, iii. 1841, p. 112.