Letter from Prof J. David Pye to the 5th Earl of Cranbrook suggesting that the Earl wrote the paper in memory of D. Lack as a solo author as he (Pye) did not contribute much to the research [see also "Pages 3, 6, 7, 8 of manuscript likely for paper on echolocation written in memory of D. Lack"]

Letter from Prof R. L. Usinger to Dr H. Elliott McClure on procurement of specimens of Cimicids, in particular Paracimex and Loxaspis for chromosome studies. Letter has handwritten note from McClure to the 5th Earl of Cranbrook

Letter from Prof. Dr. K. H. Voous to the 5th Earl of Cranbrook on the difficulty in distinguishing Collocalia esculenta and linchi

Letter from Prof. M. A. Webster to the 5th Earl of Cranbrook on the on benefits of bird's-nest

Letter from Professor Donald R. Griffin to Dr K. M. Chester on the good quality of the thesis of Dermot M. Smyth

Letter from R. de Naurois to the 5th Earl of Cranbrook on swiftlets of New Caledonia

Letter from R. F. Smith to the 5th Earl of Cranbrook informing him cheques were no longer acknowledged as received under the new Banking Act 1961. The firm could not find the Earl's order for the headphone compatible with RE. 321 Recorder, but would act on his earlier order for type AP14 headphones

Letter from R. G. Busnel to the 5th Earl of Cranbrook requesting for a reprint of article from Ibis, 1965, 107, no. 2, 258. He also requested for four or five Collocalia heads either dried or preserved

Letter from R. K. Brooke to the 5th Earl of Cranbrook on Apus caffer breeding

Letter from R. W. Sims to Dr Kenneth C. Parkes concerning swiftlets of the Phillippines and of Malaysia