Well, according to a dozen Alaskan Duck Experts from the Palmer Hay Flats, the mallards around my section of marsh 5 miles up stream from them are all feeding off the spawed out salmon or the eggs from said salmon.
The few birds I have taken the time to perform a necropsy on all had mostly some water plant that looked like a milfoil. There were seeds as well, but I never tried to determine what they came from. Early September they are still going after insects.
I have yet to take a fish duck even though the said experts tell me my marsh us nothing but fish ducks. What is funny is that each morning I am out there I can watch flights of mallards way up high going out to the Hay Flats and bypassing the marsh I am in. They are coming from a remote marsh another 3 miles up the river and filled with more salmon. However, the Hay Flats experts tell me that my ducks don't come to their marsh since there is too much habitat between the two. They must think that ducks don't migrate or something.
Mike tell me about this "wild millet" you have over there. I have not been looking for moist soil plants over here, just water plants, but learning what is out there in the wild may help me find some better spots.