Ornithology is a branch of zoology that concerns the study of birds. Etymologically, the word "ornithology" derives from the ancient Greek ὄρνις ornis ("bird") and λόγος logos ("rationale" or "explanation"). Several aspects of ornithology differ from related disciplines, due partly to the high visibility and the aesthetic appeal of birds. Most marked among these is the extent of studies undertaken by amateurs working within the parameters of strict scientific methodology.