1. Arnall L., Keymer I.F.: Bird Diseases, pp. 374–375. T.F.H. Publications, Neptune City, N.J., 1975
2. Bennett R.B.: Care and breeding of budgerigars, canaries and foreign finches, pp. 186–187. Arco, New York, 1961
3. Hare T.: cited in Strouds Digest on the Disease of Birds, p. 246. T.F.H. Publications, Neptune City, N.J., 1964