It seems with Woodducks by us that they just come in later when you shoot at the roost...They don't seem to leave if their is a good number but simply come in about 10 mins. or so after shooting hours when they were coming in 10 mins. before. With Mallards it's something I will never do. They are most likely to get up and go elsewhere. Which they could change their feeind area as well...I've had that happen a couple times when I first got into hunting.