On June 4th, Air China flight CA4307 had a mid-air collision with a foreign object that left a significant dent in the plane's nose. After the pilots reported performance problems, the plane returned to Guangzhou, where the flight had originated. The damage shown indicates a glancing blow with a lightweight object, and Chinese authorities identified it as a probable bird strike. However, there is no known bird that can fly at 26,000 feet. The highest flying species is the Bar-headed goose, which can cross the Himalayas at an average altitude of 18,000 feet. They have been observed as high as 21,000 feet when over the Himalayas, but not over China. They fly at much lower altitudes over the lowlands, and Guangzhou is in the plain of central China north of Hong Kong and over a thousand miles from Tibet. The region is not on the typical migration pattern of the Bar-headed goose.