European herring gull
The European herring gull is an increasingly common roof-nesting bird in urban areas of the UK, and many individual birds show little fear of humans. The Clean Air Act 1956 forbade the burning of refuse at landfill sites, providing the European herring gull with a regular and plentiful source of food. As a direct result, European herring gull populations in Britain skyrocketed. Faced with a lack of space at their traditional colonies, the gulls ventured inland in search of new breeding grounds. Dwindling fish stocks in the seas around Britain may also have been a significant factor in the gulls' move inland.