Adaptations of High-Altitude Birds
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There are some birds that fly so high, they’re up there with commercial aircraft. The Ruppell’s griffon vulture, for example, can fly at heights of up to 37,073 feet (11,300 meters), while a plane might cruise somewhere between 32,808 and 39,370 feet (10,000 and 12,000 meters)!
Of course, going that high up isn’t without its challenges, and not just any bird would have the physiology to handle it. Some of our avian buddies are equipped with special adaptations that allow them to soar high above the rest of their feathered comrades.
Physical & Physiological Adaptations of High-Altitude Birds
If you’ve ever heard anyone talking about their experiences in mountain climbing, or perhaps you’re a seasoned climber yourself, you’ll understand some of the challenges humans face as we enter higher altitudes. The air higher up is not as dense and therefore contains fewer oxygen molecules which, of course, makes it harder to get the oxygen we need through breathing. When this happens, we’re less physically able and may experience symptoms such as headaches and nausea.
Amazingly, there are humans that live at high altitudes and it’s thought that this is because of special adaptations to their physiology. The same happens in certain bird species that fly at much higher heights.
On top of the risk of hypoxia (low oxygen levels), birds flying at great heights have to also deal with challenging external conditions like high winds and much lower temperatures. Again, this requires special adaptations to cope with these extremes.
Respiratory Adaptations
If you’re a bird and you want to handle the lower oxygen levels at high altitudes without developing hypoxia, then you need a pretty reliable respiratory system.
Birds that are able to fly at such great heights have much more efficient respiratory systems that allow them to take more oxygen from the air. One of the main reasons for this is that the system moves oxygen over the surface of the lungs when inhaling and when exhaling.
Looking at the lungs of high-altitude species, we can see that they’re typically a lot larger than birds that are found at lower altitudes. Moreover, the air sacs inside the lungs are larger, so that when the bird inhales, it can take in more of those limited oxygen molecules.
What’s more, the gas exchange within the lungs is significantly more efficient and the ability of oxygen to bind to hemoglobin is also much better in these birds. The parabronchioles in the lungs of these bird species allow for cross-current gas exchange, resulting in more oxygen being extracted from the air.
Muscular Adaptations
As well as an adapted respiratory system, high-altitude birds also have adaptations to the circulatory system; most notably, a larger heart. The benefit of this is that the organ is far more efficient at moving blood around the body and delivering what limited oxygen there is. Not only this, but in some species, such as the bar-headed goose, the left ventricle of the heart has a greater number of capillaries allowing for increased output of blood.
You’ll also notice that high-altitude birds tend to have much larger wing spans. This allows them to fly at greater heights without using up as much energy. Moreover, this design means that they can fly for much longer periods at a time. On top of this, these birds have a lower wing loading value, which means they have to use less power to stay in the air.
Feather Adaptations
Feathers perform several functions, two of which include keeping the bird warm and making it aerodynamic. However, different types of feathers serve different purposes, and you’ll notice that high-altitude birds tend to have more downy feathers which are designed for insulation. Not only can we see that these birds have thicker down in the first place, but by monitoring this, it’s hoped that we can gather data on which species are more vulnerable to climate change.
In addition to denser down feathers, high-altitude birds are also more aerodynamic, which means they find it easier to move through the strong wings even during longer flights. Migratory birds seem to have more pointed wing feathers which are longer and less resistant to wind.
Cardiovascular Adaptations
As I mentioned earlier, bar-headed geese have a more complex network of capillaries in the heart which enables them to take in more oxygen. But this isn’t the only cardiovascular adaptation of these incredible birds.
For example, high-altitude bird species typically have a greater concentration of hemoglobin – a molecule within the red blood cells, responsible for carrying oxygen around the body. The benefit of this is that their muscles receive more oxygen, allowing them to work more efficiently at great heights.
Not only this but the number of capillaries around the muscles is much greater than those in low-altitude birds.
Metabolic Adaptations
Before taking on a long migration, many bird species will gorge themselves on food ready for the extended flight. In some cases, these birds can fly for thousands of miles without touching the ground, so they need to use their energy wisely.
Throw high altitude into the mix as well, and you could potentially have a recipe for disaster if the bird cannot use energy as efficiently as possible, but that’s where their metabolic adaptations come in.
Their metabolism has been shown to increase by up to 16 times compared to when they’re resting, which allows them to extract as much energy as possible from their food and avoid succumbing to the effects of hypoxia.
High-Altitude Birds with Unique Adaptations
There are some pretty impressive birds that can reach insane altitudes. But in order to survive the extreme conditions high in the sky, they need some special adaptations. Here are some of the world’s most amazing high fliers.
Ruppell’s Griffon Vulture (Gyps rueppellii)
Hailed as the highest flying bird on the planet, Ruppell’s griffon vulture is able to soar at heights of up to 36,000 feet (10,972 meters). Sadly, this was only discovered when one individual impacted with a plane at a whopping 36,100 feet (11,003 meters). Despite low pressure and a lack of oxygen, the species is able to remain in the air thanks to an alteration of one of its proteins.
As a result of this adaptation to the hemoglobin Alpha D, the bird is able to absorb more oxygen even when they’re at staggering heights.
These large birds of prey are found only in the Sahel region of Africa and not only fly high but also fly for as long as seven hours a day in search of food.
Bar-Headed Goose (Anser indicus)
The bar-headed goose has been the subject of a lot of studies regarding how well birds cope at high altitudes. This species is found across Asia and Russia and not only flies high in the sky but also prefers to nest at high altitudes in a mainly mountainous habitat.
Bar-headed geese have several physiological adaptations that put them in a much better position to handle the low-oxygen environments through which they fly. They take the steepest migration of any bird from Mongolia to the Indian subcontinent, during which time, their large lungs, increased numbers of mitochondria and higher hemoglobin and capillaries allow them to fly freely without suffering from altitude sickness.
Moreover, studies have shown that not only does the blood of bar-headed geese have a higher affinity for oxygen, but it also works more efficiently at varying temperatures because of its thermal sensitivity.
On top of this, the bar-headed goose has a very large wingspan of up to 62 inches (157 cm) as well as incredibly strong wing muscles. This allows the bird to fly up to more than 7,000 feet (2,133 meters) in some extreme cases. Although, generally speaking, they’ll migrate at between 4,000 and 6,000 feet (1,219 and 1,828 meters).
Andean Goose (Chloephaga melanoptera)
The Andean goose is a species of waterfowl found in Peru, Bolivia, Argentina, and Chile. These are large birds that live at high altitudes and can fly as high as 19,685 feet (6,000 meters). One of the ways that they are so easily able to cope with this is through their complex lung structure.
Compared to other birds, Andean geese have more blood vessels in the lungs as well as features like a larger respiratory surface which improves the efficiency of gas exchange.
Even when they’re not in flight, these birds live at high altitudes of up to 9,842 feet (3,000 meters), and the oxygen-rich hemoglobin in their blood is another way that they live comfortably in these conditions.
Ruddy Shelduck (Tadorna ferruginea)
In order to get to their breeding grounds in the north, the ruddy shelduck needs to take a long flight over the Himalayas which could see it reaching heights of around 13,123 feet (4,000 meters). However, there have been confirmed flights where ruddy shelducks have soared as high as 22,309 feet (6,800 meters)!
With a rusty orange colored plumage and white markings, these large ducks are certainly beautiful but they’re also physiologically amazing. But the problem is that we just aren’t sure how yet.
Scientists are yet to observe such high flights in any duck species, but unfortunately, they’re going to have to do more research to find out exactly what it is that makes these birds so easily able to climb as high as they do.
Andean Condor (Vultur gryphus)
The Andean condor has the largest wingspan of any raptor; up to 10.5 feet (3.2 meters)! But it needs these large wings in order to fly as high as it does. The size of the wings means that the bird can soar and glide through the air as opposed to flapping which would expend a lot more energy. This also enables them to fly for long periods of time. In fact, it’s been shown that they only flap their wings for 1% of the time that they’re in the air.
As well as large wings, Andean condors also have another distinguishing feature; their bald heads (although the males have a crest, making them the only species of vulture with sexual dimorphism.) It’s thought that their bald heads allow their skin to be exposed to the sterilizing effects of dehydration and ultraviolet light at high altitudes. (source)
Alpine Chough (Pyrrhocorax graculus)
In most cases, the Alpine chough won’t descend any lower than 4,921 feet (1,500 meters), although they’re also commonly found at 9,842 feet (3,000 meters). This ability makes it the highest flying of all European species. While they are small birds, their wingspan is relatively large in comparison to the body, allowing them to glide and save energy when flying. It also has a fanned tail that allows it to make the most of any updrafts.
Another thing that’s truly amazing about the Alpine chough is the fact that it can breed at such high altitudes. This is possible because the eggs of this species don’t have as many pores, which means they retain moisture more easily even when the air pressure is low.
These birds breed and feed at high altitudes and this is all thanks to the adapted respiratory and cardiovascular systems. They are able to increase their rate of breathing which prevents them from being susceptible to the lower levels of carbon dioxide in the air.
