Science says some turtles can breathe through their rear ends, but the real biology is stranger than you can imagine

“Breathing through the butt” sounds more like an internet joke than vertebrate physiology. Yet for a small group of freshwater turtles, there is real science behind the bizarre claim. These turtles still have lungs and breathe air, but while submerged they can also extract oxygen directly from water using specialized structures connected to the cloaca, the multipurpose opening reptiles use for excretion and reproduction. In some species, this form of aquatic respiration is so effective that it helps the animals remain underwater for hours, and, under the right conditions, far longer.

The mechanism has nothing to do with turtles inhaling air through their rear ends. Instead, it is an extraordinary example of bimodal respiration, in which an animal obtains oxygen through more than one respiratory route.

How can a turtle 'breathe' through its rear end?

The key structures are called cloacal bursae. These are paired sac-like extensions connected to the cloaca. In species highly adapted for aquatic respiration, the inner surfaces of the bursae contain numerous branching projections called papillae packed with blood vessels.


The turtle rhythmically pumps water into and out of these chambers. Dissolved oxygen in the water then moves across the thin respiratory surface into the blood.


This happens through diffusion. According to Fick's principle of diffusion, gas exchange becomes more effective when there is a large surface area, a thin diffusion barrier and a favorable difference in gas concentration or partial pressure across that barrier.

A highly vascularized cloacal bursa provides precisely that kind of interface.

The white-throated snapping turtle, Elseya albagula, offers a remarkable example. Researchers Sean FitzGibbon and Craig Franklin of the University of Queensland found that aquatic oxygen uptake supplied 70 ± 8% of total oxygen requirements in the turtles they studied. The cloacal bursae themselves accounted for 48% of aquatic oxygen uptake, making them the major underwater respiratory surface in that experiment.

The Fitzroy River turtle takes underwater breathing even further

Another Australian species, the Fitzroy River turtle, Rheodytes leukops, is even more specialized for underwater gas exchange.

Its cloacal bursae contain highly vascularized, branching papillae. The turtle actively pumps oxygenated water across these structures, allowing oxygen to enter its circulation without requiring a trip to the surface.

This adaptation appears closely connected to where the turtle lives. Rheodytes leukops inhabits Queensland's Fitzroy River system and is associated with flowing, well-oxygenated water.

Researchers Matthew Gordos, Colin Limpus and Craig Franklin demonstrated just how closely the system responds to oxygen availability.

When Fitzroy River turtles were placed in well-oxygenated water, they maintained cloacal ventilation during extended dives. When oxygen levels in the water fell, their heart rates declined and the turtles shifted toward metabolic depression, conserving oxygen rather than extracting as much from the surrounding water.

Science says these turtles can stay aerobic during remarkably long dives

Normally, an air-breathing animal submerged for long periods eventually begins running short of oxygen. Cells then become increasingly dependent on anaerobic metabolism, which can lead to lactate accumulation and acid-base disturbances.

The Fitzroy River turtle can delay that problem.

In another study, researchers examined Rheodytes leukops during dives lasting as long as 12 hours. Despite repeated dives exceeding two hours, plasma lactate remained below 3 millimoles per liter, and researchers found no evidence of the expected metabolic acidosis associated with extensive anaerobic metabolism.

The researchers concluded that aquatic respiration helped the turtles remain aerobic during prolonged dives.

That is the important distinction behind the catchy “butt-breathing” description. The cloaca isn't replacing the lungs. It is providing an additional pathway for gas exchange that reduces how often some turtles need to surface.

Cold water can make the trick even more powerful

Temperature adds another fascinating layer. Turtles are ectotherms, meaning their body temperature and metabolic rate are strongly influenced by their environment. In colder water, metabolism generally slows, reducing the animal's demand for oxygen.

At the same time, colder water can hold more dissolved oxygen than warmer water.

For an aquatic-respiring turtle, that combination can be extremely useful: lower oxygen demand meets greater environmental oxygen availability.

Researchers studying Myuchelys bellii, another Australian freshwater turtle with specialized cloacal bursae, recorded dive durations exceeding 15 days during winter. The researchers attributed these extraordinary periods partly to aquatic respiration and low winter water temperatures.


Researchers studying Elseya albagula similarly found that water temperature influenced surfacing behavior. Their work drew on optimal breathing theory, which predicts that diving animals should balance the benefits of remaining submerged against the energetic costs and risks associated with traveling to the surface for air.

Not every turtle can breathe this way

This is where the viral version of the story often goes wrong. Having a cloaca does not mean every turtle can perform meaningful cloacal respiration. Many aquatic turtles possess cloacal bursae, but those structures can serve different physiological functions.

A study by Charles Peterson and Darren Greenshields noted that cloacal bursae have been proposed to play roles in buoyancy control, ion transport and other functions, while specialized aquatic respiration through them is particularly well documented in several side-necked turtles.

Aquatic turtles can also exchange gases through other surfaces, including the skin and the lining of the mouth and throat. Which route matters most depends heavily on the species.

So saying “turtles breathe through their butts” turns an extraordinary physiological adaptation into an oversimplification.

What some turtles actually do is far more sophisticated. They actively move water across highly vascularized respiratory structures, exploit diffusion to pull dissolved oxygen into their blood, adjust their cardiovascular and metabolic physiology as oxygen availability changes, and use cold conditions to reduce their oxygen requirements.

Their lungs haven't disappeared. Evolution has simply given some turtles another place to find oxygen.

FAQs

Do turtles really breathe through their butts?

Some freshwater turtles can perform cloacal respiration, but “butt breathing” is an oversimplification. Water is pumped through the cloaca and across specialized, highly vascularized structures called cloacal bursae, where dissolved oxygen can diffuse into the bloodstream.

Can turtles stay underwater all winter without breathing air?

Some species can remain submerged for extraordinary periods during cold conditions. Researchers recorded winter dives exceeding 15 days in Myuchelys bellii. Cold temperatures reduce metabolic oxygen demand, while aquatic respiration can supplement oxygen obtained through the lungs.