Proportion of Mallards feeding using different feeding methods (from Green, 1998).
In a comparative study of duck feeding behaviour, Andy Green found out that neck dipping and upending were the predominant feeding methods in Mallards. Ferruginous ducks, a species of diving duck, did not upend and barely used the neck dip, diving was overwhelmingly the most commonly used method.
You can watch Mallards upending in this short video:
More informationAndy J. Green (1998). Comparative feeding behaviour and niche organisation in a Mediterranean duck community Canadian Journal of Zoology, 76, 500-507 : 10.1139/z97-221