- Written by Nadia O’Carroll
As impressive as these altitudes may be, they are modest compared to the highest bird flight ever recorded, a Ruppell’s Griffon (a species of vulture) collided with a jet at a height of 11,552 metres above sea level over the Ivory Coast in Africa.
The highest altitude migrant is the Bar-headed Goose (Anser indicus) which has been observed flying at heights of 10,175 metres. Every year flocks of this species make the return trip across the Himalayas from winter quarters in India to breeding grounds in Tibet. As a comparison the cruising altitude of many commercial passenger aircraft is between 9,200 and 10700 metres.
Conditions at these altitudes are different from those at sea level – the air is so thin that helicopters cannot fly and the level of available oxygen is so low that kerosene will not burn. Humans may experience altitude sickness above 2,400 metres due to the same problems that the Bar-headed Goose has overcome by some of the following adaptations to its pulmonary, cardiovascular and muscular systems:
Oxygen - the percentage of oxygen (21%) in the atmosphere is the same at both sea level and high altitudes (up to 21,000 metres). However because the air pressure decreases with altitude, the number of oxygen molecules in a given volume drops as altitude increases. As a result it is difficult for an animal to absorb oxygen into its body and oxygen deprivation or hypoxia can occur. The Bar-headed Goose overcomes this problem by a number of physical adaptations such as a large lung to blood volume ratio; air sacs which recirculate breathed air to extract more oxygen; effective haemoglobin which quickly absorbs oxygen into the bloodstream; muscles which contain a high volume of capillaries. The Bar-headed Goose is also able to pant or ventilate for long periods without affecting blood vessels in the brain, so the bird can continue to think clearly. In mammals such as humans, hyperventilating impairs cognitive function.
Low air pressure - reduces drag so it is easier for the bird to fly forward but lift is also reduced so the bird has to flap its wings more to stay aloft. The Bar-headed Goose has huge powerful flapping wings that have a large surface area in relation to its size and a pointed shape, which reduces wind resistance.
Low temperatures – the strenuous aerobic and metabolic activity produces heat which is retained in downy feathers, this prevents ice forming on the wings in the extreme cold of high altitudes.
Powerful winds - of over 200 kms per hour occur at high altitudes, with its powerful wings the Bar-headed Goose can fly at 80 kms per hour unaided and with tail winds can attain great speeds and cover hundreds of kilometres in a day.