The city does not. They're sustained by the natural resources of the park and pond itself. Canadian geese use the pond seasonally as well. People do feed them regularly with bread and other 'treats'
The pond is a particularly altered natural environment. The number of ducks and geese at the pond would not be sustainable naturally. The only way that the ducks and geese are able to survive is because people feed them.
Thanks! Your answer is awaiting moderation.