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Autumn Syracuse

How Do Penguins Breathe — aka “Do Penguins Have Gills?”

Penguin anatomy and physiology

How Do Penguins Breathe — aka “Do Penguins Have Gills?”

Autumn L. Syracuse, Educator I

As our penguins swim through the pool in their exhibit at the Aquarium of Niagara, another common question we are asked is “How do penguins breathe? I don’t see their gills.” As we have previously discussed, penguins are in fact a bird. They rely on breathing oxygen from the air like other birds, and like us too. Though perfectly adapted to life as an aquatic predator, penguins cannot stay underwater indefinitely. Their respiratory system contains lungs, like other air-breathing animals, as well as air sacs, a common trait among birds themselves.

First, a little penguin anatomy – birds breathe differently than humans

Let’s first discuss how respiration in birds compares to respiration in humans. When we breathe air, humans will inhale, drawing air through the windpipe, each of the 2 branches of bronchus, and into each lung. Once inhaled, the oxygenated air will travel into the alveoli where gas exchange will happen. When exhaling, the deoxygenated air will travel in reverse from inhalation. The lungs will compress, and push the air out of the alveoli, through the bronchus, and back out through the windpipe. This type of air flow is referred to as “bidirectional”.

In birds, both inhalation and exhalation will occur, but will flow in a “unidirectional” path. When birds inhale, the ribs expand and oxygenated air travels in the same way as humans: through the windpipe, into the bronchus, and into the lung. Gas exchange happens in the parabronchi within the lung. When exhalation happens, the deoxygenated air does not go in reverse like in humans. The air flows out of the lung via a second bronchus that will draw the air out through the windpipe (Scheid, 1979). Both inhalation and exhalation occur in each species. However, they contrast in the direction of air flow. Let’s look at it like going out for a jog. In human-respiration, air travels in an out-and back-motion. If you want to run a mile, you may start at your house, run a half mile down the street, then turn around to come back. In bird respiration, air travels in a circular motion. If you want to run a mile, you could leave your house and travel in a loop and return home to complete that mile.

penguin anatomy and physiology
Figure 1. Anatomy of bird respiratory system.

Birds have air sacs in addition to lungs

In addition to lungs, birds also have air sacs. Nine of them to be exact: 2 cervical air sacs, 1 interclavicular air sac, 2 anterior thoracic air sacs, 2 posterior thoracic air sacs, and 2 abdominal air sacs. Upon inspiration, air moves into the 4 posterior air sacs. During expiration, the air then moves through the parabronchi in the lungs to allow gas exchange to take place. The second inspiration draws air into the 5 remaining anterior air sacs. The second expiration will then allow air to exit the body through the trachea. It will take two breathing cycles (inspiration and expiration) for air to move completely through the bird respiratory system.

This process may seem a bit confusing, and it was to me at first also! Tracing the air flow through the system makes it a bit easier to understand.  Here is a video to better understand how this process works:

How does a penguin hold its breath so long?

So how does this help penguins while they’re diving and holding their breath? It’s not so much the process, but the physiology of their lungs. Many studies have been done in regards to marine mammals and how diving affects their lungs. The ability to collapse their lungs when diving helps against the extreme pressures of the deep ocean. This also prevents gas exchange from happening at deep depths, which in turn prevents nitrogen from building up in the lungs. If you’re familiar with SCUBA, one of the risks of diving is this build-up of nitrogen in the lungs, especially on rapid ascent.  Diving birds however, and birds in general, have very rigid lungs and surrounding structures which cannot collapse as marine mammals do. Though this sounds counter-productive when diving, it does help when ascending to the surface. Penguins will use their natural buoyancy to spend less energy coming back up to the surface.

Remember the unidirectional flow of air in bird lungs? This process allows only oxygenated air to come in contact with the parabronchi, and allows the lungs to store 30-45% of its body’s total oxygen compared to marine mammals storing between 5-20% of their total oxygen (Ponganis, St. Leger, and Scadeng, 2015). By storing more oxygen, this will help provide the muscles in the wings and shoulders with enough energy to propel themselves deeper into the ocean. After reaching these depths, the air within the lungs and air sacs will then allow the penguin to ascend to the surface naturally. 

Penguins are some of the best divers in the underwater world, utilizing oxygen to its fullest. Next time you’re at your local zoo or aquarium, check out these amazing animals and see if you can hold your breath up to the penguins’ expectations!

Penguin anatomy and physiology
Figure 2. Two patterns of breathing to help penguins hold their breath for diving deep.
Credit: Karl Tate, LiveScience Infographic Artist

Did you know about how penguins breathe? Let us know what you learned. Also, please help us continue to learn more about penguins by donating to Penguins International. We more than appreciate your support!

You can also read more about penguins in the following blogs:


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Scheid, 1979. Respiration and Control of Breathing in Birds

Ponganis, St. Leger, and Scadeng, 2015. Penguin lungs and air sacs: implications for baroprotection, oxygen stores and buoyancy


Credit: Karl Tate, LiveScience Infographic Artist

Do Penguins Have Knees?…and other frequently asked questions

Penguin knees

Do Penguins Have Knees?…and other frequently asked questions

by Autumn L. Syracuse, Educator I

“Do penguins have knees?” and “So what is a penguin?” are two of the most common questions I hear regarding our penguin colony on display at the Aquarium of Niagara ( Before we talk about penguin anatomy, let’s discuss what a penguin is exactly, first. It’s hard to imagine that these chunky bipeds that don’t fly — but swim — are indeed birds. Ostriches, emus, and rheas are pretty easy to identify as birds with their fluffy plumage of feathers. So why does it seem odd to include penguins in this group of flightless birds? Are all birds descended from one common ancestor?

Birds are: warm-blooded, air breathing, egg-laying, covered in feathers, and possess a bill. Now let’s take a look at penguins: They check all the boxes! “But why are they birds? They are so funny looking!” Although outwardly different from most other birds, penguins still possess many characteristics of other avian species. Let’s get down to the bones of it.

Penguin knees

Okay, so do penguins have knees?

A penguin’s skeletal structure is laid out in the same general pattern as other birds. One obvious characteristic of a bird skeleton is the keel, or sternum. This is designed to be very wide and flat, but lays perpendicular to the ribs. This large bone helps to attach the flight muscles and tendons, which is very important in both form and function to flight. And since penguins “fly” through the water, which is denser, they too need to rely on the keel and flight muscles for propulsion. 

Another important adaptation that varies from other flighted (volant) birds is the density of their bones. Most birds we see flying in our yards and neighborhoods have skeletons with bones that are hollow. This creates a skeleton that is extremely lightweight, allowing the birds to be able to lift off into flight. Penguins would not benefit from bones of this same density. Penguins need to be able to dive underwater to hunt for their fish, and hollow bones would make them too buoyant. To help with this, penguin bones are solid and heavy, helping to give them more weight in order to dive deep.

Penguin knees are tucked up inside their body

Penguins are designed to be streamlined and hydrodynamic, so having long legs would add extra drag. Having short legs with webbed feet to act like rudders, helps to give them that torpedo-like figure. If we compare bird anatomy with humans, we would see something a bit peculiar. By taking a look at the side-by-side image in Figure 1, you can see how their leg bones compare to ours. What most people mistake for knees are actually the ankles of the birds. This gives the illusion that bird knees bend opposite of ours. The knees are actually tucked up inside the body cavity of the bird! So how does this look inside of a penguin? In the images below, you can see boxes surrounding the penguins’ knees. 

Penguin knees
Penguin knees
Colored boxes highlighting the location of penguin knees.

Imagine yourself wearing an oversized shirt, and pulling it over your knees so that only your ankles and feet are showing. Now imagine you’re trying to walk forward in this position. I bet you’d waddle too! This design gives the penguin an advantage in the water to help them swim quickly to catch food or avoid predators. On land, they tend to be slower and clumsy, which makes them more prone to predators. For Antarctic penguins, they rarely encounter predators on land, so having larger bodies isn’t detrimental. For other species in temperate or tropical climates, the water tends to be a bit safer place.

Originally, penguins were classified in the same group as other flightless birds (Ratites). After multiple studies, it was discovered that penguins evolved from flying birds, which were separate from the ancestors of other flightless birds. Mitochondrial DNA has further suggested their relationship to other seafaring flighted birds such as albatross, frigatebirds, and loons. In 2006, more genomic testing suggested that birds of the Ciconiiformes order (storks, gannets, plovers, and boobies) were their closest living relatives (Watanabe et al. 2006). 

Paleontologist Ewan Fordyce with a model replica of a Waimanu penguin.

It is still uncertain as to what other bird species may be related to penguins. But from finding and examining their fossilized bones, we have an idea of what they were like nearly 60 million years ago. Known by the genus name Waimanu, these ancient penguins may hold the record for the oldest evidence of bird lineage. Scientists believe that the extinction event that wiped out the dinosaurs during the Cretaceous period, also eliminated almost all bird species. After this catastrophe, it is believed that modern day penguins evolved from the few species that had survived, evolving quickly over a short amount of time—in relation to Earth’s history (Fordyce and Ksepka, 2012).

“So what kind of animal are they?” All of the evidence points to birds, but it still leaves questions unanswered. After learning of this fossil evidence, it leaves me with this question: “Are penguins birds? Or are birds penguins?” When we take a look at other body systems and explore their behavior, things become more “black and white.”

Like our penguin blogs? Sign up for our newsletter to get them right in your inbox!

Have you ever wondered before reading this if penguins have knees? Let us know what you think, and what you learned. Also, please help us continue to learn more about penguins by donating to Penguins International. We more than appreciate your support!

You can also read more about penguins in the following blogs:

Penguins International
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Denver, CO 80250 USA
phone: 628-400-7301

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