Swans normally find enough food in the wild without supplementary feeding and the large population of swans on the Avon suggests that the tidal part of the river is no exception. Swans eat aquatic vegetation, which their long necks equip them to take from the riverbed. They also take the molluscs that cling to the vegetation or mud, and eat small fish, frogs and worms.  However, a few people persist in feeding swans and other wildfowl on the estuary.  While unprocessed whole grain is unlikely to do the birds any real harm in the long term, it is no substitute for the proper diet that the birds themselves will seek out.  Bread, in particular, contains unnatural yeasts, sugar and salt which can upset the birds’ digestive systems.  Artificial feeding also encourages changes in the birds’ behaviour; they start associating people with food and, therefore, tend to follow and pester other people who may not be interested in feeding them.  Aggressive swans can be a real danger to other river users.