A. Newton, Dict. Birds, 1893, pp. 293, 294.
W. A. Forbes, P.Z.S. 1882, pp. 208-212.
The East American form of P. flavirostris is separated as P. americanus by Mr. Ogilvie Grant, Bull. Ornith. Club, vii. 1897, p. xxiv.
Cf. E. Newton, Ibis, 1861, pp. 180, 276; Layard, op. cit. 1863, p. 248.
Cf. Seebohm, Birds of the Japanese Empire, 1890, p. 212.