A strange shaped object was floating in the air for 5 min in Yokohama City, very low then disappeared in the cloudy sky.I just reported an UFO flying up and down in a gravitating way, going upward and downward very quietly, birds were flying around it but the birds were being pushed away, causing the bird to fly downward. First sight I thought it was a helium balloon, but too big for a helium balloon, so I ask my girlfriend for binoculars, but couldnt position the UFO insight. Then I thought it was plastic but not plastic, UFO was floating as if it was looking for something. The color was like aluminum foil but more of a plastic look. It changed color shape so couldnt tell the shaped of the UFO. I have seen many aircrafts, balloons, gliders but this wasnt neither. But as the birds were taunting the UFO it flew higher into the sky and disappeared. I really believe now so shocking. It was like it was hiding...((NUFORC Note: Witness elects to remain totally anonymous; provides no contact information. PD))