The Patent US2073922, filed Oct. 19, 1936 and registered March 16, 1937 by Oscar Cobia of Los Angeles, describe a « Bird And Sing Whistle ». The shape is well-known, with a rounded nose-cap like the metal Humanatone or the Magic Nose Flute...
But there is a real innovation : a set of interchangeable "U" or "V" shaped pieces of metal, to be inserted in the air duct and offering different labium shapes (« different tuning appliances can be inserted exchangeably »), and thus, different intonations or quality of sound.
The description suggests the usage of a finger to modulate the sound :
« With a device as described here, and, particularly, by means of the tuners, an operator is able to whistle, warble, chirp, and create a great many different sounds, simulating different birds, such as canaries, and mocking birds, and also simulate whistling and singing of different people, and, by inserting a finger between mouth and plate, create different variations, as by shaking and vibrating the inserted finger. »
Here is the full patent claim :
« a device of the class described having a nose-cap with an aperture to align with the nostrils of an operator, a mouth-plate extending downwardly from the nose-cap and having an aperture to align with the mouth of the operator, a chamber securely mounted over the back of the nose-cap and having a portion extending back of the mouth-plate so as to form a narrow channel closely related to the mouth aperture, and a tuning member having a cut-out and being shiftably inserted into the channel so that a portion of the cut-out aligns with the mouth aperture. »