List of sources:
Journal of the South African Ornithologists' Union, 1905-1909, Vol. 1-5: Duncan's article and lists of members and office bearers.
South African Association for the Advancement of Science. Report, 1910, 1918: Lists of members.
South African Journal of Natural History, 1919, Vol. 1(2), pp. 274-277: List of members of the South African Biological Society.