There's a river running through the center of town here, and just on the edge of downtown it has a small dam that was built sometime during the industrial revolution. On one side of the dam there's slow, deep water flowing in a wealthy and neighborhood; on the other side it's fast, shallow and noisy water running through the main commercial/entertainment district.
On the quiet side, flocks of gulls come to rest at night, several hundred birds sitting silently in the center of the river, almost in single file, slowly drifting towards the dam. At a precise point about 200 meters from the fall, when it starts getting noisy, the birds in front wake up, fly a couple hundred meters upstream, and go sit at the back of the line to rest again. The end result is a sort of bizarre conveyor belt formation with this large flock of birds quietly floating backwards, all facing in the same direction against the current, with their comrades continuously flying over their heads until it's their own turn to take to the air, over and over again.
It's really neat to look at but dang these suckers can't possibly get a good night's sleep like that. First one to figure out what's happening is gonna be frikkin' Gull Moses.
