I will take some better pictures this afternoon.
I can only take credit for copying "rebelcowboysnd"'s idea.
It is just a 3" piece of PVC about four feet long with a cap glued to one end and two 90 degree elbows at the other. Lay it on it's side, fill it with water, stand it up, and the water will not come out until they drink it. It's a gravity, vacuum, physics, hydraulics, mystery kind of thing.
The six feathered creatures are Black Sexlinks.