We use 2 different whistling sounds.
Type. 1
Cover the hole on the sound chamber with your index finger and blow “trrr” softly into the call three times (trrr, trrr, trrr), pause for 10 seconds (trrr, trrr, trrr), pause for 10 seconds (trrr, trrr, trrr).
Repeat this series of sounds every 5-10 minutes for a 30-40 minute stand.
Type. 2
Cover the hole on the sound chamber with your index finger and blow 4 short, soft thrusts of air in close succession, finish with a long thrust of air for 3 seconds where you remove your finger from the hole as you start blowing and let the sound fade out towards the end (ju-ju-ju-ju-jullllliiiiii). Paus for 10 seconds and repeat.
Repeat this series of sounds every 5-10 minutes for a 30-40 minute stand.