bill and coo vs lovebird

bill and coo

verb
  • To exchange loving and affectionate behaviour, such as caresses and kisses. 

  • To coo and rub beaks as a prelude to mating. 

lovebird

verb
  • To express romantic affection openly. 

noun
  • Any small parrot from one of the nine species within the genus Agapornis. Sometimes they are kept as cage birds and are noted for their affection towards each other. 

  • One of the members of an openly affectionate couple. 

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