Brown pelicans: Cruising the West Coast waves

The pelicans looked like they were engaged in a high-stakes game of “chicken” with the crashing surf.

On a recent road trip down the coasts of Oregon and Northern California, I watched in wonder as lines of brown pelicans cruised low over the ocean — mere inches from the water and directly in the path of oncoming waves — then swooped up at the last second before the waves crested and broke.

Below are some photos of these daring pelicans in action.

Why do pelicans fly this way, a mere wingtip away from a tumble in the surf? Is it for fun — to boost their “pelican adrenaline,” or does the behaviour serve some other purpose?

Turns out these flying tactics are actually energy conservation tactics. The pelicans are combining two helpful aerodynamic effects — “ground effect” (also called “compression gliding”) and “dynamic soaring” (sometimes called “wave-slope soaring”) — to travel farther, faster, on less fuel.

Ground effect

When a bird (or a plane, for that matter) flies above land or water at a height less than or equal to its own wingspan, the air that naturally funnels between the lower surface of its wing and the ground becomes compressed. This compressed, denser air acts as an “air cushion” that supports the bird, allowing it to glide farther — without flapping its wings or losing altitude — than it normally could.

Ground effect is stronger the closer to the ground a bird flies, but it doesn’t last forever. Eventually the air cushion will dissipate, and the bird must flap its wings, regain altitude and rebuild speed before it can settle back down to that sweet spot inches above the water.

Birds can employ ground effect over any surface, but calm water is the best as it’s devoid of obstacles. When you add building or breaking waves to the picture, pelicans can combine ground effect with the second tool in their energy-saving toolkit: dynamic soaring.

Brown pelicans riding the ground effect air cushion ahead of an approaching wave. Photo: Caroline Ross

Dynamic soaring

Birds employ dynamic soaring by repeatedly flying back and forth between areas of different wind speed, using the energy differences between the zones to their advantage.

In the case of waves, air gets piled up (and moves faster) in front of a building or breaking wave, then falls away (and slows down) in the trough behind the wave. Pelicans riding the ground effect use these air currents — particularly the faster current in front of a wave — to cover more distance with less effort.

A 2021 study on dynamic wave soaring of brown pelicans describes the effect this way:

“At the coastline…, pelicans can…be seen tracking the crests of shoaling waves just outside the surf-zone, often in formation…. In this fashion, they appear to gain forward speed and thus kinetic energy [from the air in front of the wave], which they then convert to height, peeling off and upwards just as the wave begins to break. This altitude is then used to glide downwards…to the subsequent approaching wave. By linking individual waves together, the birds can travel hundreds of meters or more with limited flapping.”

“Wave-slope soaring of the brown pelican” by Ian A. Stokes and Andrew J. Lucas, Movement Ecology Volume 9, 2021. Published online 22 March 2021.

Putting it all together

Pelicans cruising low in the surf zone thus combine a ride on the ground effect “air cushion” with a “push and lift” from the dynamic air in front of each wave to get the most bang for their flying buck. In this way, pelicans can cover more distance and expend less energy, which means they don’t need to consume as much food to get places.

So these pelicans aren’t playing in the surf, they’re surfing air currents. And they’re not seeking adrenaline, but ease.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s