Colonel Legge had a strong interest in ornithology. He spent his free time in Sri Lanka (then Ceylon) studying the birds of the region, a work started by Edgar Leopold Layard, which led to his authorship of "History of the Birds of Ceylon", comprising two quarto-sized volumes, with coloured plates by Keulemans, published in three parts between 1878 and 1880 in London. The work consisted of over 1200 pages with 34 plates in colour; some woodcuts became the standard book on the subject due to their high quality. He was also the secretary of the Royal Asiatic Society in Colombo. Part of his collection of Ceylonese birds were presented by him to the Natural History Museum at South Kensington, and the remainder was given to the museum at Hobart. He also published short notes on the ornithology of Ceylon and later Tasmania.