Well, darling, "hen" is actually a gender-neutral pronoun used in place of "he" or "she." So, it's not about being common or proper, it's about being inclusive and respectful. So, go ahead and use "hen" if you want to keep up with the times and show some consideration for all gender identities.
"Park Avenue" is a proper noun, because it is a place. Proper nouns like this should always be capitalized.
proper
common
common
It is a proper noun, because it is the name of a specific thing.
nest?
"Park Avenue" is a proper noun, because it is a place. Proper nouns like this should always be capitalized.
proper
They are all vertebrates.
common and proper
common
common
It is a proper noun, because it is the name of a specific thing.
Chickens.
it's a common noun. a proper noun would be Spider-Man.
Proper
Pencil proper or common noun