Montagu is best known for his Ornithological Dictionary (1802) and he contributed significantly to early knowledge of British birds. He showed that many hitherto accepted species were invalid, either being birds in summer or winter plumage or males and females of the same species. His study of harriers resulted in the discovery that the Montagu's Harrier was breeding in southern England, and he was also involved in the first British records of Cirl Bunting, Cattle Egret, Little Gull and Gull-billed Tern.
Barbara and Richard Mearns - Biographies for BirdwatchersReference