The dominant sonic force at Slimbridge is hidden in plain sight.
Common reeds reveal just a fraction of their sounds externally. There are unheard vibrations within the plants, inside the stems; playful, jostling scrapes and knocks, shaped by constantly evolving, turbulent airflow through the wetlands.
You are listening to the internal sounds of the reeds, recorded using special microphones attached directly to the stems. It is a microscopic fabric: a hidden study in aerodynamics.