Here’s the physics of why ducklings swim in a row behind their mother

There’s physics to having your ducklings in a row.

By paddling in an orderly line behind their mother, baby ducks can take a ride on the waves in her wake. That boost saves the ducklings energy, researchers report in the Dec. 10 issue of the Journal of Fluid Mechanics.

Earlier measurements of duckling metabolism showed that the youngsters saved energy when swimming behind a leader, but the physics behind that savings wasn’t known. Using computer simulations of waterfowl waves, naval architect Zhiming Yuan of the University of Strathclyde in Glasgow, Scotland, and colleagues calculated that a duckling cruising in just the right spot behind its mother gets an assist.

When a duckling swims on its own, it kicks up waves in its wake, using up some energy that would otherwise send it surging ahead. That wave drag resists the duckling’s motion. But ducklings in the sweet spot experience 158 percent less wave drag than when swimming alone, the researchers calculated, meaning the duckling gets a push instead.

Like good siblings, the ducklings share with one another. Each duckling in the line passes along waves to those behind, so the whole brood gets a free ride.

But to reap the benefits, the youngsters need to keep up with their mom. If they fall out of position, swimming gets harder.  That’s fair punishment for ducklings that dawdle.