This explanation of "bird whistle" is from the book, "The Golden Age
of Automatic Musical Instruments," by MBSI member Arthur A. Reblitz,
published by the Mechanical Music Press, Woodsville, New Hampshire;
copyright 2001, posted at the web site of Musical Box Society
International:  http://www.mbsi.org/glossary.php?letter=B 

  bird whistle.
  Metal organ pipe of special construction, often about 1-1/2" in
  length, with an extension of the open end immersed in a container of
  oil or glycerin, causing the pitch to warble in imitation of a canary.
  Used in certain theatre organs and photoplayers for sound effects,
  and rarely in orchestrions, such as the Capitol Bluebird Orchestra,
  for novelty purposes.

Robbie Rhodes
Mechanical Music Digest