I've noticed lately that my male Pekin starts bobbing his head up and down very fast and quacking whenever he and the other Pekin (a female) are playing in the water. He stretches his neck tall, then dips his head down so that his bill touches his chest over and over. Usually it happens when I fill their dunking litter box with fresh water, or when I'm showering them with the hose. I've never seen him do it away from the water, and I've never seen the female duck do it at all. What does it mean? I'm so curious, and I can't figure it out! The only guess I have is that he's excited over all the water...? But why doesn't the female do it too?