black cap vs laughing gull

black cap

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

laughing gull

noun
  • An American gull (Leucophaeus atricilla); in summer the head is nearly black, the back slate color, and the five outer primaries black. 

  • A common European gull (Xema ridibundus). 

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