As they ride the wind, vultures seek dead things, not dying things, using a sense of smell far more highly developed than any other bird's. They can detect a dead mouse under leaves from 200 feet up. They are discriminating, preferring corpses between two and four days dead. (The turkey vulture entry in the definitive Birds of North America Online does note, "Takes live prey occasionally in unnatural situations.")
Read the whole thing here. The story discusses puking as a defensive move by beset vultures. Owing to an traumatic incident when she was a child returning from church with her grandparents, my wife has an exaggerated wariness of vultures dining on roadkill and starts braking and swerving a hundred yards away when she spots them in the road. She says I would not be so sneeringly dismissive of her fears if I had ever experienced vulture vomit up close.