One who specialises in the study of birds
A
Biologist
B
Naturalist
C
Zoologist
D
Ornithologist
Correct Answer: Ornithologist
One word substitute is Ornithologist.Biologist: an expert in or student of the branch of science concerning living organisms.
Naturalist: an expert in or student of natural history.
Zoologist: an expert in or student of the behaviour, physiology, classification, and distribution of animals.
Ornithologist: a person who studies or is an expert on birds.