Duck soup food was for sale on the same narrowboat that was selling the painted canal ware. As most of us were growing up, going 'to feed the ducks' in our parks, canals and rivers on left-over bread and cake was often a family tradition. (I guess most of us tried eating the stale bread ourselves too!) What people often don't realise is that bread and starchy food can actually be harmful to birds. OK, so you might only be giving them a couple of crusts - but, especially in places like Saltaire, there is a steady day-long stream of people doing exactly the same thing. The birds are stuffed full of bread and the canal is often littered with soggy rotting lumps, causing bacterial and algal growth. The bread is not good nutrition for birds (ducks, geese, swans, pigeons and little birds too) leading to obesity, bloating and difficulty flying. The young can grow up malnourished and it discourages the birds' natural feeding behaviours. The waste also encourages pests. So it's not 'Let them eat cake' but 'Let them eat grapes, oats, birdseed, defrosted peas' - and yes, £1-a-bag duck food too. See here for the full article from birding.about.com.