Wow, I guess I have a new found respect for these guys, especially geese. Another pilot I was talking too said geese can dive pretty deep into water to fetch fish as well. Think about it... their body can go into water, generate enough lift from sea level to FL390, can handle temperature ranges from warm to approximately -50C (@ FL390), has lung capacity to breathe at FL390 and they have an advanced navigational system, etc.
It is clear that whoever designed these guys knew what they were doing!!!
