Avocets Black necked grebe Common terns

Today was another good visit to Fairburn Blackcaps chiff chaffs willow warblers and whitethroats all singing along the riverbank trail. From Bob Dickens hide had a great view of the Black necked grebe, spotted by my friends from Norfolk, the avocets are still there on the islands -although its hard to get good views from Bob Dickens hide surrounded as they are by blackheaded gulls. I got a much better and satisfying view of a pair of avocet from Charlies hide where they are much closer and easier to see. This pair were also mating so looks like they plan to hang around:) A juvenile lesser black backed gull did something interesting apart from annoying the resident pair of lapwings. He found a huge shellfish which looked like an oyster or clam and proceeded bash it on the rocks flying up to drop it at one point.However he didn't get a meal losing the shell in a crevice from whre he couldn't retrieve it. A common tern was fishing in front and behind Charlies hide before resting up on the perches in Village lake alongside a heron and a cormorant. Does anyone know the purpose of the platform in front of the village viewing station? osprey?