Complex sentence: Coues led great expansions of the knowledge of North American bird life, helped found the American Ornithologists' Union in 1883, edited approximately 15 volumes of journals, memoirs, and diaries by famous Western explorers and fur traders.
Split into simpler sentences: Coues led great expansions of the knowledge of North American bird life. He helped found the American Ornithologists' Union in 1883 and edited about 15 volumes of journals, memoirs, and diaries by famous Western explorers and fur traders.