Hydrologist
An entomologist.
A language expert is commonly referred to as a linguist. Linguists study the structure and usage of language, including grammar, syntax, semantics, and phonetics.
Marine biologist.
The proper name for the Jan pierewiet bird is the Bokmakierie. Its scientific name is Telophorus zeylonus.
A person who studies the formations and changes of glaciers, is a glacier geologist.
Rhea
Yes, because 'fish' and 'bird' refers to a whole category of something, while a proper noun refers to a single entity(such as someone's name or the name of a city)
If you don't know a bird expert, look it up in a Field Guide.
The proper name for the bird sometimes known outside of Australia as a laughing jackass is the Laughing Kookaburra.
The proper name for the bird sometimes known overseas as a laughing jackass is the Laughing Kookaburra.
avine, or more commonly, avian