Why do pelicans surf?

The answer comes in the form of a 2021 study by oceanographers Ian Stokes and Drew Lucas that sheds light on how and why these birds surf.

Published in Movement Ecology, their paper "Wave-slope soaring of the brown pelican" breaks down the physics behind the birds’ aerial surfing technique. The authors set out to quantify just how much energy pelicans save by riding the updrafts created by waves – a behavior they've dubbed "wave-slope soaring" (WSS) and we call “surfing”.

Look at this pelican flying just above the water's surface, zipping down the line of an approaching wave. The bird is taking advantage of the upward movement of air pushed by the advancing wave, gaining lift without flapping its wings

Figure 1 of the paper, captured by Simone Staff.

To model wave-generated wind that makes this possible, Stokes and Lucas simplified things by using a solitary wave – imagine a single, perfect wave moving across an otherwise calm lake. While not exactly like the wave trains we typically see at the beach, this approach allowed them to clearly map out the air movements around the wave. The solitary wave has a specific shape based on physics, but understanding its exact form isn't important to understand the overall process.

What is important is how this wave generates wind in front of it.

Figure 4 of the paper, which depicts a solitary wave moving to the right. Red areas are regions of rising air and blue are regions of sinking air.

Their model reveals a fascinating pattern: as the wave moves forward, it creates a region of rising air in front of it and sinking air behind. A pelican positioned just right can ride this updraft, getting an extra boost that complements the "ground effect" lift they already experience from flying close to a surface.

Surfing leads to huge energy savings for the pelican.

According to the study, pelicans that surf can reduce their energy expenditure by up to 70% compared to regular flight. This efficiency allows them to cover vast distances along the coastline without wearing themselves out.

Of course, like all scientific models, there are some simplifications. Real-world waves are more complex, and factors like wind direction can further influence the air currents. An offshore breeze, for instance, might give the birds an additional push as it follows the wave's face.

What makes this study one of my favorites is how easily observable it is. On any given day in coastal areas like San Diego, you can watch pelicans surfing their little avian hearts out. While you might not see them pulling off gnarly turns, I have a feeling they are more than capable of doing so.

This open access paper is available to everyone. The math does get gnarly, uses perturbation theory, and will probably not make a lot of sense to the casual reader. But, take a look under the hood of the science publication vehicle and give it a try. Surfing is all about getting out of your comfort zone, and learning the science behind it is the same.

Further Reading:

The paper

Solitary Wave or "Soliton”

Ground Effect