Arthur Hay, Viscount Walden, 9th marquess of Tweeddale (1824–78)

Ornithologist. Joined the Grenadier Guards in 1841, retiring as colonel in 1863 having served in campaigns in India and the Crimea. President of the Zoological Society of London, 1868–78. Known as Viscount Walden from the death of his elder brother in 1862; succeeded to the marquessate in 1876. FRS 1871.