Although in general, feeding the ducks is not recommended.

If you insist on feeding the ducks, visit your local feed store and buy a scientifically formulated poultry starter with a crude protein content of 27% or greater. Use this food until about mid-August, then switch to a food with a much higher carbohydrate content (wheat, barley, or corn, for example), because ducks start putting on fat for migration at that time. See this link. Or this link.

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NH GeeseDucks 2012