Crawlies with Cri: Bird’s Breath

Bird’s Breath

Ever wonder how birds have boundless energy? Not to mention how they fly and fly thousands of miles during migration and fly with ease at altitudes that would have us gasping?
This week’s Crawlies will answer those questions.
The simple answer is “birds breathe much more efficiently than we do.”
Let’s do a quick overview of how mammals breathe. We do so via a two-step bidirectional airflow – inhale, exhale, done. Our lungs are filled with little air sacs (alveoli) clustered around our bronchi tubes.
When we inhale through our mouth or nose air goes down the trachea and into these sacs. Then via osmosis oxygen and carbon dioxide are exchanged. We hold onto that awesome oxygen and send it out to our blood and tissues.
Meanwhile we’re still chock full of carbon dioxide, which we get rid of by exhaling. During the time we exhale, we’re deprived of oxygen. Bummer.
Due to our built-in inefficiency, we can’t muster the energy necessary for flight. Okay, also we don’t have wings, but even if we did…
It takes an incredible amount of energy to fly. This also explains why birds eat so much.
Fun fact: Hummingbirds are the peak example of “eat to fly.” They must eat the human equivalent of 150,000 calories every day just to do normal hummingbird things – like aggravate each other. For migration they may double their body weight over the few days before they travel just so they can survive the journey.
If they were stuck with bidirectional breathing, they’d never get off the ground.
So, what gives birds a lung-up on the competition?
Remember, we breathe air straight into our lungs and all the CO2 extraction and exhalation heavy lifting is done right there.
Birds have a circular system made up of two sets of air sacs with the lungs in between. It’s a looped system so birds are never without oxygen. It’s also a four-step breathing process versus our two-step.
Birds still inhale and exhale, but to complete a full “circuit” they need to do so twice.
The clearest example I found was this:
Imagine a bird taking their very first breath.
First inhale – the air enters through the bird’s nostril-like nares on either side of the bird’s beak. It goes down the trachea into the posterior air sacs.
First exhale – the air is pushed from the posterior air sacs into the lungs where via osmosis the nifty oxygen is extracted and sent on its way.
Second inhale – while new air enters into the posterior sacs, the old air is pushed from the lungs into the anterior sacs.
Second exhale – nice air goes from the posterior sacs into the lungs while CO2 goes from anterior sacs out of the trachea.
Once our theoretical “new bird” is “up and running” they have a constant flow of nifty air into their lungs and zero moments of oxygen deprivation like mammals are saddled with.
This gives birds a much higher concentration of oxygen entering their bloodstream which their birdy flying muscles need.
They still need lots of calories too, so if you’ve been contemplating putting up a backyard feeder or two (or in my case 14) now is the perfect time because our backyard feathered friends (and free pest controllers) are either starting, in the middle of or at the end of their migration and they need all the calories they can get.