Ornithology was the branch of zoology that specialized in the scientific study of birds.
Commander Hutchinson had a background in ornithology, and found the mating habits of the Arkarian horn fowl to be of particular interest. In 2369, he asked Geordi La Forge and Deanna Troi whether either of them were interested in the subject, then continued to speak about the bird even though they hadn't answered his question. (TNG: "Starship Mine")