nightingale vs songbird

nightingale

noun
  • A Eurasian and African songbird, Luscinia megarhynchos, family Muscicapidae, famed for its beautiful singing at night; a common nightingale. 

  • A kind of flannel scarf with sleeves, formerly worn by invalids when sitting up in bed. 

songbird

noun
  • A bird having a melodious song or call. 

  • Any bird in the passerine suborder Passeri, which are distinguished by a more sophisticated vocal apparatus 

How often have the words nightingale and songbird occurred in a corpus of books? (source: Google Ngram Viewer )