Waterslager walnut is one of the three types of walnuts are recognized by the World Ornithologic Organization / Ornithologique Confederation Mondiale (COM) or the Organization of the World Bird Expert. The other two types are the German Harz Roller (in Indonesia known as the Harzer) and Spanish Timbrado. Each of these types has a distinctive song and clearly distinct and easily identifiable even by new fans. Harzer have a song that resonated and long, his voice like the sound inside. The main variations of the song is nge-roll, it can be said there is always the letter 'r' in between syllables. The main variations of the song is 'hollow' roll: rorororororororo ... These variations must be used for Harzer. Another variation is to be controlled by a kind of canary native Germany this is a shot called 'Pfeiffen' or 'Flute' in which there is a space between syllables, for example: ... su-su-su-su.

However, the variation is not so unique song before discovered Waterslager and Timbrado. Harzer very well known abroad, although progress is not as fast as waterslager.

Link: ciri-ciri kenari waterslager (http://www.budidayakenari.com/2015/06/kenari-waterslager.html)