bird's nest vs incubator

bird's nest

noun
  • A structure built by a bird as a place to incubate eggs and rear young. 

  • Any of several plants having some resemblance to the typical nest of a bird, eg, wild carrot (Dauca carota) 

  • Any tangle of fibers resembling a typical nest of a bird. 

incubator

noun
  • An apparatus used to maintain environmental conditions suitable for the hatching of eggs. 

  • An apparatus used to maintain environmental conditions suitable for a newborn baby. 

  • Any apparatus used to maintain environmental conditions suitable for a reaction. 

  • A place to maintain the culturing of bacteria at a steady temperature. 

  • A support programme for the development of entrepreneurial companies. 

How often have the words bird's nest and incubator occurred in a corpus of books? (source: Google Ngram Viewer )