Possibility #1: Sometimes vultures gather and roost just to rest. Is the wind blowing? If not, they may be waiting for it to pick up so they can ride the currents. They're very heavy birds and don't like to expend more energy than necessary for flight. I'd just chill out and be glad they're around - imagine how stinky the world would be w/out them to clean up the rotting flesh!
#2: Maybe they're waiting for the sound of a hunter's gun and they forthcoming entrail pile?
#2: Maybe they're waiting for the sound of a hunter's gun and they forthcoming entrail pile?