Verified altitudes
The upper limits of our atmosphere pose extraordinary challenges for living creatures - freezing temperatures, dangerously thin air, and intense UV radiation create an environment more hostile than many deserts. Yet some birds have mastered these extreme conditions, flying at altitudes that rival small aircraft.
While most birds stay within a few hundred feet of Earth's surface, these high-altitude specialists have evolved remarkable adaptations to function in the oxygen-poor upper layers of our troposphere, where every wing beat must work harder in the thin air.
Their achievements not only showcase the incredible adaptability of avian physiology but also help us understand the absolute limits of vertebrate survival at extreme altitudes.
Gyps rueppellii
A Rüppell's vulture was recovered from the engine of a commercial airliner over the Ivory Coast in 1973, which caused the engine to fail and forced the pilot to make an emergency landing.
To put that altitude in perspective, it’s 2,500m higher than Mount Everest, around 30 times higher than the Empire State Building, or equivalent to 471 full-size tennis courts.
Grus grus
Flying at this height enables them to migrate safely over the Himalayas, avoiding eagles, where you can spot them in Spring and Fall.
Anser indicus
During migration they also fly at this height over the peaks of the Himalayas.
Cygnus cygnus
A flock of Whooper Swans was recorded travelling at this height by radar over Northern Ireland.
Pyrrhocorax graculus
Recorded at this height on Mount Everest.
Gypaetus barbatus
Milvus migrans
They can reach this height during migration to and from West Africa.
Vultur gryphus
Anas platyrhynchos
Height was recorded over Nevada, when a Lockheed L-188 Electra turboprop airliner operating a Western Airlines flight had a strike with a Mallard whilst at cruising altitude.
Limosa lapponica
This height can be reached during migration.
Ciconia ciconia
This height can be reached during migration.
There are two main scenarios for when birds fly high - for migration and whilst on the lookout for prey.
Firstly, birds fly at high altitudes during migration. The air is thinner the further up you go, which lowers air resistance and makes flying more mechanically efficient.
Secondly, birds fly at high altitudes to gain a wide view of the ground, which is advantageous when looking out for prey. For example, the Rüppell's vulture regularly flies in circles at a great height to scan the desert for carrion.
While flying at a high altitude is more efficient than flying at a low altitude, most animals, including humans, would perish at altitudes exceeding 30,000ft without serious acclimatization at least.
At the earth's surface, the air's oxygen content generally varies between 20 and 19%. At 30,000 ft, oxygen levels drop to just 6%.
High-flying birds are excellent at absorbing oxygen at this altitude, but it still requires huge amounts of energy. Some birds, such as geese, swans, and cranes, lose 15 to 20% of their body weight throughout their migratory journey!
If birds fly too high without adequate energy, they’ll have to return to a lower altitude and rest.
Birds often collide with planes. In fact, it even has its own terminology, a “bird strike”. There are an estimated 13,000 bird strikes each year in the US alone, but 65% result in no damage to the aircraft.
Geese are a prime culprit, accounting for the majority of bird strikes in the US, but starlings, pigeons, and vultures are all common.
Commercial airliners are built with failsafes for when an engine ingests a bird, and even if the engine fails or is shut down automatically, the airliner is typically able to land without much issue.
However, there have been a few fatal incidents of birds colliding with planes, including on October 4, 1960, when a Lockheed passenger plane flew into a flock of starlings, causing all four engines to fail. It crashed shortly after, killing 62 out of 72 passengers. Birds have even struck space shuttles and military aircraft. Luckily, the risk of dying from a bird strike is less than 1 in 1 billion flying hours.
Some birds have a number of specific adaptations that enable high-altitude flight. For example, they’re already acclimatized to high altitudes and have a superior hypoxic ventilatory response, enabling them to make the most of the oxygen available.
A few birds, such as the Rüppell's vulture and some hummingbirds, also possess specialized hemoglobin, a protein in their red blood cells which has a tremendous affinity for oxygen. Birds also typically have larger, more elastic lungs and can “gulp” air down their strong throats, especially in the case of geese, swans, and ducks.
Another consideration is the temperature. The temperature at 30,000ft is as low as -48F or -44.5C, which would freeze most animals to death in seconds. Birds retain heat through their feathers, but their powerful muscles also produce energy that keeps them warm.
That depends on how high the clouds are! Clouds range from low altitude varieties such as stratus and cumulus, at around <5,000ft, to cirrus and cumulonimbus, exceeding 45,000ft!
Small single-engined planes can comfortably fly at altitudes between 10,000ft to 15,000ft, and many birds can fly at this altitude. Commercial airliners typically cruise at around 30,000 to 35,000ft, and only three species of birds can fly that high - the Rüppell's vulture, Common crane, and Bar-Headed goose.