The High Efficiency of Avian Lungs

Photo by: Rick Lewis
This Great Blue Heron always has fresh air entering its lungs, regardless if it’s inhaling or exhaling, because the air is streamlined and stored in multiple air sacs. Photo by: Rick Lewis

Can you remember the last time you thought about your lungs?

For me, most days pass without giving a pause of consideration to them. That is, until I recently visited one of our restoration sites at Eden Landing Ecological Reserve and saw a murmuration of American Avocets smoothly gliding above the marsh. Their comfort and ease navigating the sky renewed my awe for our feathered friends’ coveted gift of flight. Beyond all of the physiological reasons I can’t make it on my own into the sky, just the idea of flying has me winded.

Birds have adapted to experience breath very differently than us. Like other living beings, they rely on good ole air to stay kicking. But what’s special about the avian species is a highly efficient ability to get the most out of each breath.

Ok, take a deep breath in. I’m about to get technical.

Let’s start with us. Human (mammalian) lungs are bidirectional. This means that the pathway for air to enter our lungs is the same pathway used to leave our lungs. Picture our lungs working like balloons that inflate and deflate.  In contrast, the avian species have unidirectional flow, made possible by separate entry and exit points to the lungs. Rather than a balloon, picture a bird’s lung as a windsock that has air continually flowing through in one direction.

Let’s take a Great Blue Heron for example. When the bird breathes in, the inhaled air passes down the throat just like it does for us, but right before it reaches the lungs, it splits. Some of the air enters the lung, where the oxygen is absorbed, and some of the air enters multiple adjacent cavities called air sacs.  These air sacs do not absorb the oxygen and function as storage tanks for the air. When the Great Blue Heron exhales, the old air in the lungs is released into different air sacs and eventually out through the beak and nostrils, and the fresh air stored in the first air sacs enters the lung. In this way, the Great Blue Heron always has fresh air entering its lungs, regardless if it’s inhaling or exhaling.

And here’s another twist, birds don’t have diaphragms.  So to push all this air around they rely on the simple physics of air pressure. The multiple air sacs (up to nine in some species!) exist to offer changes in air pressure, which moves air into the lungs at regulated frequencies that maximize oxygen absorption. Relative to their body mass, birds do not breathe as fast as we do.  However, this respiratory system allows birds to have consistent oxygen absorption.  It’s this unwavering air flow that contributes to their ability to sustain the high energy costs of flying.

Now breathe out. How do your lungs feel?

To learn more about avian respiratory systems check out this site.

San Francisco Bay is home to many bird species and offers habitat to migratory birds making their way along the west coast on the Pacific Flyway. Watch this video featuring the Birds of San Francisco Bay.