The avian respiratory system is the most efficient in the animal kingdom, which explains how birds get enough oxygen to power flight, even at high altitudes where oxygen is scarce. A key feature that makes avian respiration special is the fact that they have static lungs and breath unidirectionally by breathing with air sacs throughout their body instead of diaphragms common in other land animals.
When a bird draws in a breath of air, it travels through the nares (or nostrils) down the trachea into a series of posterior air sacs located in the thorax and rump—in their butts. When a bird exhales that same breath, it does not leave the body as it does with mammals but rather moves into the lung where oxygen is absorbed and carbon dioxide expelled. When a bird inhales for the second time, that same breath of air moves from the lungs into the anterior air sacs. The second and last exhalation is when the stale air leaves the bird’s body through the nares.
Every breath a bird takes requires two breathing cycles to complete a single breath, making the air passing through the lung unidirectional and always fresh and full of oxygen. Bird lungs are small and rigid, with the gas exchange region of their anatomy organized into a series of parallel tubes that bring deoxygenated blood into the lung at the opposite direction the air is flowing. This “counter-current” gas exchange is efficient and unique to bird lungs and partly enables species, such as the Bar-headed Goose (Anser indicus), to fly over the summit of Mt. Everest without issue. Human explorers, on the other hand, struggle for fresh air at 29,029 feet above sea level because mammalian lungs never expel all the stale air during exhalation, making mammalian explorers long for the ability to use their butts to breath continuous fresh air like the birds.
Chase Mendenhall is Assistant Curator of Birds, Ecology, and Conservation at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.
This indicates that a continuous, one-way airflow is provided to the lungs by the system that the air sacs create. Here, it also passes through the parabronchi, which are the parts of the lungs that carry oxygen to the air capillaries, in a single direction. Here, waste carbon dioxide is traded for new oxygen.
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When a bird breathes, air travels through nares, which are tiny, nostril-like apertures in the beak. A bird’s breathing system differs significantly from a mammal’s when you look past the well-known nostril concept and consider what happens next. This is because birds have an incredibly effective respiratory system that allows them to meet the physical demands of flight by providing their blood with oxygen, which powers their flight muscles.
Because a bird’s breathing takes two cycles to complete a single breath, the air that passes through its lungs is unidirectional, constantly fresh, and oxygen-rich. The gas exchange region of a bird’s anatomy is arranged into a network of parallel tubes that carry deoxygenated blood into the lung in the opposite direction of the air flow. Bird lungs are small and rigid. Birds’ efficient “counter-current” gas exchange, which is exclusive to their lungs, helps some species, like the Bar-headed Goose (Anser indicus), soar over Mount Everest without issue. However, because mammalian lungs never completely expel stale air during exhalation, human explorers struggle to breathe fresh air at 29,029 feet above sea level. Instead, they yearn to be able to use their butts to continuously breathe in fresh air, just like birds do.
Chase Mendenhall works at the Carnegie Museum of Natural History as an assistant curator for birds, ecology, and conservation. It is encouraged for museum staff members to blog about the special experiences and insights they have had from working there.
A bird’s breath enters through its nares, or nostrils, and passes through the trachea before entering a number of posterior air sacs in its thorax and rump—its butts. The same breath that a bird exhales enters the lung, where carbon dioxide is expelled and oxygen is absorbed, rather than leaving the body as it does in mammals. The same breath of air leaves the lungs and enters the anterior air sacs when a bird inhales twice. The stale air exits the bird’s body through the nares during its second and final exhale.
Because of their highly efficient respiratory system, birds are able to sustain their flight even at high altitudes where oxygen is in short supply. The fact that birds have static lungs and breathe unidirectionally via air sacs throughout their bodies rather than the diaphragms found in other land animals is a crucial characteristic of avian respiration.
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