Whistle down the wind

We went for a walk in Roath Park this morning and did something we could never do with the dogs and went inside the Roath Park Conservatory, a small but nonetheless interesting tropical greenhouse. In the centre, is a small pond with huge Goldfish, terrapins and a pair of South African Whistling Ducks. When we first started to walk around we were alerted to their presence by a whistling noise, which the attendant told us was unusual when there are lots of visitors around. 
The extra is one of the many swans on the lake who was washing and preening itself.