Thorburn illustrated two books on mammals, J.G. Millais's The Mammals of Great Britain and Ireland, London, 1904-6 and his own book British Mammals, London, 1920, a companion to British Birds, published five years earlier. His work is particularly admired for its careful attention to detail and the way in which he brings life onto the two-dimensional sheet. Plate 17 in British Mammals illustrates the Common Otter and the accompanying text notes that Thorburn had 'only once seen an Otter abroad during the day, when one passed close to me as he made his way along the banks of a rocky burn in Sutherland.' (A. Thorburn, Thorburn's Mammals, London, 1974, p. 44).