Whistler lived at Battle, East Sussex during his retirement, where he was a Justice of the Peace. He made one trip to India in 1928 as a guest of Admiral Hubert Lynes with the intention of studying the birds of Kashmir. Lynes was recalled to England and insisted that Whistler and Bertram Beresford Osmaston complete the bird survey. He joined the British Ornithologists' Union in 1913 and in 1940 served as its as vice-president. He visited Kashmir with Admiral Lynes and wanted to produce an account of the birds of Punjab and Kashmir; this was not completed.