Threat of birds to aircraft safety

Bird strikes against aircraft
Birds threaten the safety of aircraft in flight when they may strike and destroy the windshield at a critical moment, possibly leading to sudden decompression within the aircraft. They may also be sucked into jet intakes. On the ground, resting birds may hinder the movement of aircraft landing or taking off.
Birds can fly at very high altitudes and are regularly detected at 20,000 feet. Many birds have collided with aircraft in mid-air with disastrous results. Particular species most often involved include starlings, gulls, condors, albatrosses, several species of eagle, and particularly the whistling swan. In Europe in 1989, some 3,000 bird strikes were recorded against aircraft, although only 30 caused damage requiring repairs.
Aggravated by 
(D) Detailed problems