For caged birds, when refilling their food bowls, don't throw the old seed away. Usually there are many unused seeds in the bowl. Instead take 2 containers of the old seed outside on a mildly windy day and pour the seed from one container to the next. The wind will blow away the used seeds (because they are so light), and all you will have left are good seeds. No more waste!
I couldn't agree more - I feed the local water fowls, pigeons & parrots with my leftovers. Just love watching them all gobbling the seed.