I am in Port Hope Ontario. I grew up on a large bay filled with marshy wildlife. Never in all those years did I see any Mallards diving for food. Currently where I live in Port Hope Ontario, we have a river that is now at its low point, and I was very surprised to see mallards, male and female both diving underwater for food. There are plenty of cormorants around and perhaps they are learning to mimic those birds. I looked at several sites that said no, Mallards don't dive, but I can affirm that they certainly do! Thanks!