American Black Vultures aloft all alone, but gregarious on the ground (at Bear Creek Pioneers Park)

Seen, in large numbers, on Christmas Day 2012 in Addicks Reservoir in West Houston. Note that the black vultures -- unlike other animals -- are not deliberately kept on park grounds as zoo animals, but visit with pot-bellied pigs and exotic birds in their pens when not out on patrol high above the highways looking for road-kill. 

Peaceful cross-species co-existence, apparently. 

American Black Vultures hanging out at the pig pen at Pioneers Park

Vulture soaring above the canopy of trees in Addicks Reservoir at dusk