. >> the catastrophic event moved bird lover marianne scott to action. >> the high-rises are the biggestt the statistic is for stories or less where the most fatal collisions occur. >> as executive director of the building association of philadelphia, she is to convince the number of buildings or turn off lights both inside and outside between midnight and 6 a.m. during migration seasons. >> my on large, people don't know there's a problem. they are shocked to hear when i say that there might be 300 million birds traveling across the country now. >> in fact, the night before we went on patrol with stephen, an estimated 660 million birds were in the skies over the u.s. in the midst of their spring migration north. that makes for a busy morning. an injured oven bird is placed in a paperback for transport to the wildlife center clinic for rehabilitation. then, stephen helps an apparently stunned bird struggling to regain its sense of direction and get on its way. next, an injured yellow throated warbler. at the entrance of an office building, a fox safeguarding the body of a dead bd. >> i a