Just Keep Swimming: The Physics of Ducks

Have you ever wondered why you organize your ducks in a row? It’s physics! 

Ducklings swimming behind their mother in ponds and lakes is a common sight. Similarly, when we often see birds flying in a V-shape formation¹, this is to conserve energy. Each bird flies slightly above the bird in front of them to reduce wind resistance. But what about ducklings?

 In a recent study², researchers tried to answer these questions: 1) why are these ducklings swimming in a formation? 2) what is the best swimming formation? and 3) how much energy can they save?

Using a mathematical and numerical model, researchers have observed two phenomena, dubbed “wave-riding” and “wave-passing”. Normally, when a duckling swims on its own, it kicks up waves and uses energy. The ducklings’ movement across the water forms wave drag, produced by the friction of their bodies against the water. Any amount of drag against the water slows the ducklings down, causing them to lose energy in the water when ducklings swim solo.

However, when ducklings ride the waves generated by their mother, they save their energy and even get a boost. This is because there is a ‘sweet spot’ behind the mother duck that allows ducklings to turn the wave-drag positive and push the duckling forward. Ducklings in the ‘sweet spot’ experience 158% less wave-drag than swimming alone! 

This wave-riding benefit can continue if the ducklings are in a single-file formation. By the third duckling, the wave-drag is almost near zero. This state of balance, or equilibrium, lets the subsequent ducklings act as a wave-passer: Ducklings in front are passing the waves’ energy to the next duckling without losing energy.

We have a lot to learn from waterfowl and their formation swimming. This kind of breakthrough may be applied to the shipping industry, by designing modern freight-carrying vessels (e.g., a water-train) to transport more cargo without the extra fuel cost. Now that’s what I call beak performance! 

References

1. F. REED HAINSWORTH; Precision and Dynamics of Positioning by Canada Geese Flying in Formation. J Exp Biol 1 March 1987; 128 (1): 445–462. doi: https://doi.org/10.1242/jeb.128.1.445

2. Yuan, Z., Chen, M., Jia, L., Ji, C., & Incecik, A. (2021). Wave-riding and wave-passing by ducklings in formation swimming. Journal of Fluid Mechanics, 928, R2. doi:10.1017/jfm.2021.820