The bird migration season - which brings hundreds of foreign birdwatchers to Israel but is a headache for the air force and Ben-Gurion Airport - has already begun, according to the the International Center for Bird Migration Research at Latrun, which is run jointly by Tel Aviv University and the Society for the Protection of Nature. The center's radar facility at Yad Lashiryon in Latrun warns the airport and the air force about the movements of the large birds, which travel south from Europe and Asia in the fall, passing over Israel to spend their winters in Africa, and vice versa in the spring. Dr. Leonid Dinevitz, an immigrant scientist from the former Soviet Union who used to be a general in the Russian army, operates the radar equipment that he brought with him from his native country. The storks and other feathered creatures that fly over Israel cause nervousness among pilots. They also attract large numbers of Israeli and foreign bird-lovers to the Hula Valley, where the birds are fed and take a rest before flying on.