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Crowing
Not sure how this would work with ducks but if you're using a stock tank you could add mosquito fish (gambusia). As long as they have a place to hide, like cinder blocks, they will reproduce quickly and they may even hibernate overwinter if the tank isn't too shallow and you break a hole in the ice. Some local governments give them out for free. I had to buy mine but they're not expensive and 10 quickly became hundreds.