For centuries, mute swans were known as 'birds royal' because only the king or a few specially favoured subjects could keep them. They were often served up, roasted, at banquets - a roast swan must have required a very large plate!
Flight feathers from the female swan were used as writing implements then known as 'pen quills' and later as 'quill pens', until the 'quill' was left out and only the word 'pen' remained. So our present-day ballpoints etc. take their name from the female swan!
Over the last 30 - 40 years, the mute swan population has fluctuated. Many swans living on rivers where coarse fishing is popular died because they were swallowing lead fishing weights with their food. Lead is very poisonous. Since 1987, the use of lead weights has been banned in the UK and its swan population has recovered. Another hazard for swans is carelessly discarded fish hooks and lengths of nylon fishing line - both can cause a swan to suffer a painful death.