How high do these birds fly?

Question: How high do these birds fly?
- Keywords:
  bird,
  fly,
  high
Asked by harrykilner to St Kilda Wren, Common Crane, Brown garden snail, Barn Owl, Emperor Dragonfly on 21 Nov 2017. This question was also asked by hannahannah, miamia.
- St Kilda Wren answered on 21 Nov 2017:
  
  We don’t know exactly how high wrens can fly, but we can make a guess. Some wrens migrate all the way from Scandinavia to Spain – a distance of over 2,500 km! Migrating birds tend to fly high to take advantage of the high winds and lower air pressure, so migrating wrens might fly quite high indeed. The St. Kilda wren doesn’t migrate, though, and you’d almost always find them flying between walls, bushes, and scrub at waist height or lower.
- Common Crane answered on 23 Nov 2017:
  
  Higher than the sky! We can fly almost as high as airplanes – 33,000 ft (10,000 m)! I am one of the highest-flying birds 8)

Question: How high do these birds fly?