What's the greatest height at which a bird has collided with an aircraft?
On November, 29 1973 a bird strike occurred at an altitude of 11,300 m over Abidjan. The engine was shutdown during the collision, and was not restarted.

Altitude


  The altitude is that recorded by the pilot shortly after the impact,
  which damaged one of the aircraft’s engines and caused it to be shut
  down. The plane landed safely at Abijan without further incident.


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Species

It was determined the bird was a vulture:


  The remains of the vulture consisted of five complete and 15 partial
  feathers from the wings (secondaries, lesser, and underwing coverts),
  tail, neck, and breast. Sufficient details arc apparent in these
  feathers to allow their certain identification as G. rueppellii, using
  comparative material in the U.S. National Museum of Natural History.


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Rüppell's vulture is a specie weighting 7 to 9 kg and living 40 to 50 years:


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Record

Wikipedia confirms this is the highest collision recorded in the history of aviation:


  An aircraft over the Ivory Coast collided with a 
  Rüppell's vulture at the altitude of 11,300 m (37,100 ft), the current 
  record avian height.


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Why such altitude for a bird?

This is well above Everest height, why does this bird flies so high, where there are not so many preys, pressure is only 25% of the pressure at ground level and temperature is about -57°C?


  The reason suggested is that thinner air allows faster flight without much
  effort and saves precious energy. Flying at such a great height,
  vultures face almost no physiological problems with regard to
  breathing; they have much more efficient breathing system than other
  living beings, including humans.
  
  Their flow of blood enables oxygen to be extracted from air, with far
  greater efficiency than any other living being. If the flight is in
  cloudless condition, low temperature at great heights too does not
  bother them.


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Birds at high altitude


  The previous record altitude for a bird-aircraft collision was of a
  Mallard (Anus platyrhynchos) at 21,000 ft (Manville, Wilson Bull.,
  75:92, 1963), based on feathers that I identified from the strike.
  That collision occurred between Battle Mountain and Elko, Nevada, on 9
  July 1962. 
  
  Other high-altitude records of birds include:  
  
  sightings of migrating geese at 29,000 ft, over the Himalayas (Griffin,
  Bird Migration, Natural History Press, Garden City, N.Y., 1964), and  
  
  soaring Bearded Vultures (Gypaetus barbatus) at over 24,000 ft.


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Vultures are a known threat to aviation, as are other birds flying high:


Images and data taken from Science Focus article

In 2010, in Scotland, a Rüppell's vulture participating to a display was caught in a wind and was lost. Aviation operators had to be notified, in case the vulture was still in the vicinity.


  With a wingspan of 10ft, it could do a lot of damage to a large
  aircraft. But it's also half the size of some of our small training
  aircraft and it could take one of them, or even a helicopter, right
  out.


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Damaged compressor after a bird strike (not the involved aircraft):


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