Migration can often be a long and difficult journey for animals.  For the bar-headed goose, migration often entails flights over the highest mountains in the world: the Himalayas. Bar-headed geese have been observed flying at altitudes as high as 30,000 feet.  At such a height, the thin air contains only a quarter of the oxygen as air at sea level.  Complicating the feat is the fact that while in flight, geese consume as much as 20 times more oxygen than normal.

So how can these birds still support the exertion of flying in such a low-oxygen setting?  Graham R. Scott, a doctoral student at the University of British Columbia, and his colleagues have found that they the answer may lie in the bird’s muscles.  Scott and his colleagues compared the pectoral muscles of the bar-headed goose with several related species.  They found that the muscles were identical in all but two aspects: a greater number of capillaries around the cells and a greater number of mitochondria near the cell membrane in each cell. 

Thanks to these two adaptations, the oxygen absorbed by bar-headed geese does not need to diffuse as far to produce energy.  Scott and his colleagues theorize that bar-headed geese slowly evolved these unique features alongside the rise of Himalayas, which are one of the youngest mountain chains on Earth.