black cap vs sea crow

black cap

noun
  • A square of black fabric worn on the head by a judge delivering a death sentence. 

sea crow

noun
  • The razorbill. 

  • The Western jackdaw. 

  • The chough. 

  • The skua. 

  • The cormorant. 

  • The blackheaded pewit, and other gulls. 

  • The coot. 

How often have the words black cap and sea crow occurred in a corpus of books? (source: Google Ngram Viewer )