robins crest/robin's crest/a robin crest - Possessive regarding anatomy

[Mynameisjr]

I am having trouble finding the grammatical way of writing an animals anatomy. I am trying write about a crest on a bird specifically on a robin. Would I write robins crest, robin’s crest, or a robin crest?

Thank you

 

[emsr2d2]

I am having trouble finding the grammatical correct way of writing an animals anatomy. I am trying to write about punctuate the words for a the crest on a bird, specifically on a robin. Would Should I write "robins crest", "robin’s crest" no comma here or "a robin crest"?

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Please note my corrections above. Your first suggestion is incorrect. The second is correctly punctuated. The third might be possible depending on context. In order for us to give you a firmer answer, please provide us with a complete sentence containing the phrase.
Out of curiosity, why did you add the indefinite article only to your third suggestion?

 

[jutfrank]

Do robins have crests?

 

[emsr2d2]

Do robins have crests?

I wondered the same thing! British robins definitely don't. However, I discovered recently that what I call a robin is nothing like a robin in the States, nor in Spain. I assumed the OP had a particular bird in mind.
@Mynameisjr - out of curiosity, which bird are you trying to describe?