Bar Headed Goose
A pale grey goose with an orange beak and legs and two striking black bars on the head. It lives in central Asia. It is monotypic (males and females look the same) and mates for life.
The bar-headed goose is famous as it is widely believed to make the highest altitude migration on earth. While there was an anecdotal report of a flock of bar-headed geese being heard flying over Mt Makalu (the fifth highest mountain on earth), an unconfirmed report of them being seen flying over Everest has become legend. Such a migration would be incredibly demanding – at altitude the ambient pressure is dramatically reduced, meaning that there is less oxygen available and that the air can support less lift for flight (particularly for species that flap, like geese). This has puzzled biologists and physiologists for years:
"there must be a good explanation for why the birds fly to the extreme altitudes... particularly since there are passes through the Himalaya at lower altitudes, and which are used by other migrating bird species" Black & Tenney (1980).
As part of a large international research project, led by Bangor University and primarily supported by the BBSRC (grant BB/F015615/1) and the Max Planck Institute, bar-headed geese have now been GPS tracked (Hawkes et al. 2011 PNAS http://www.pnas.org/content/early/2011/05/27/1017295108 and available here for download as a PDF file) flying over the Himalaya and data reveal that they do not normally fly higher than 6,300 m elevation, flying through the Himalayan passes rather than over the peaks of the mountains. This altitude is clearly still very impressive (equivalent to Everest Camp II) and challenges even the fittest human climbers. Without proper acclimatisation to such altitudes, mammals suffer from high altitude related sickness very quickly, and in some cases this can be fatal.
It has also been long believed that bar-headed geese use jet stream tail winds to facilitate their flight across the Himalaya. Surprisingly, latest research has shown that despite the prevalence of predictable tail winds that blow up the Himalayas (in the same direction of travel as the geese), bar-headed geese spurn the winds, waiting for them to die down overnight, when they then undertake the greatest rates of climbing flight ever recorded for a bird, and sustain these climbs rates for hours on end.
Bar-headed geese are known to have a suite of physiological adaptations to help them deal with the low Oxygen (hypoxia) conditions at altitude: