1974 126 p., 34 figs, paperbound. Thesis. With author's dedication.We added: Lanyon & Gill, 1964. Spectrographic Analysis of Variation in the Songs of a Population of Blue-winged Warblers (18 p., 9 figs) / Becker, 1977. Geographische Variation des Geanges von Winter- und Sommergoldhähnchen (37 p., 22 figs) / Marshall, 1950. THe Function of Vocal Mimicry in Birds (12 p., 1 plate).