Interesting Duck Behavior

I've seen quite a bit of this lately...no idea what it means. In a group, a Mallard hen (I've only seen hens do it) will drop her head to the water surface, stretch out her neck and paddle furiously...looking like a submarine speeding across the water. NOT being pursued or heckledy by any other duck, and NOT appearing to be looking for food...it appears to just be some kind of 'game' behavior. Most amusing.

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