1) Animal scientist 2) Bird watcher 3) Bird-studier 4) Zoologist 1) Audubon 2) Birder 3) Birdman 
• (n.) One skilled in ornithology; a student of ornithology; one who describes birds.
A scientist who studies birds.
Scientist who studies birds.
Or`ni·thol'o·gist noun [ Confer French ornithologiste .] One skilled in ornithology; a student of ornithology; one who describes birds. 
A scientist practicing ornithology (e.g., researching, managing or teaching).
[n] - a zoologist who studies birds
scientists who study bird behavior
an individual that studies birds
a person who studies birds and bird behaviors
Professional, who studies birds.
noun a zoologist who studies birds
Scientist who studies birds.
[SAT terms] a scientist who studies birds[Literary terms] a scientist who studies birds