It’s Biology
I live in a big city, so I don’t need a car to get around. I rely on my legs that inevitably get tired and often find myself wishing I could use my husband like a human Segway, but people standing on each other for transportation would be even weirder than this duck using its friend as a surfboard.
Our feathered friends can get away with using their friends as a taxi because they have a biological excuse. It’s how they show each other who’s boss and establish the pecking order. While all ducks do it, female ducks stack on top of one another more often than the drakes.