How high can birds fly

Question

How high can birds fly

Answer 1

Well, some birds don't fly either.  Penguins dive deep.  Birds can fly from elevation 1 foot to heights over the Himalayan Mountains.  Many songbirds never fly higher than the trees they live in.  Many migrating birds fly at height from 1000 to 15000 feet.  Usually the larger birds fly higher.  The majority of migration occurs at night.

Answer 2

They could probably fly as high as they wanted to, until the air becomes too thin and they start passing out due to lack of oxygen.

Generally they stay low, where the food is.

Answer 3

If I remember correctly the greatest altitude a bird flies at is the tundra swan at about 30,000 ft.  

Answer 4

Pretty high, until they get too tired or the air gets to thin so that they pass out or can't get any higher.