King Solomon's Ring
Can't find a larger image, but this is one of the more pleasing cover designs from many editions of Konrad Lorenz's King Solomon's Ring, first published in German in '49, in English from 1951 - most recent edition is a Routledge Classics paperback.
This is another nomination from Armand Leroi, the best-known work by the one of the more intriguing authors one could choose - the Viennese goose lover, ethologist, joint Nobel Laureate with Tinbergen in '73, theorist of animal domestication and racial decline. You can read a capsule biography of Lorenz here.
The book is a brilliant series of essays on animal behaviour, has immense charm and conveying several concepts still important in the field. One the other hand, there's a well-documented essay which gives a view of the book informed by Lorenz's well-elaborated commitment to Nazism here.
So a man whose career remains controversial - he undoubtedly had some odd ideas about wolves, but his geese loved him...