David & Rob.
This digiscoped image has been heavily cropped but you should be able to make out the browner shape of the Bittern just off centre-right. It soon started moving and then disappeared from view. During our leisurely stroll to two of the hides we heard both Water Rail and several Cetti's Warblers. A number of sightings of Marsh Harriers, mainly males and just when neither of us had our cameras ready a fly past by another Bittern!