In general, scrap ducks aren’t much on quacking. The best some of them can manage is a high-pitched, strangled approximation. Wigeon, pintails, and greenwing teal whistle. Various manufacturers make pintail calls with which you can make the calls of all the whistling ducks, and greenwing teal respond especially well to a peep on the whistle. And there are special gadwall calls. Sometimes a mallard call works magic on scrap ducks. One slow day, a friend blew a screaming hail call at a tiny dot high overhead out of boredom, and we watched in disbelief as the duck, a drake gadwall, instantly dropped from the heavens into our decoys as if it had fallen through a hole in the sky.