For some reason, stores do not carry bird watering devices except for bird baths or tiny little water bottles meant for caged birds.
This instructable shows how to convert a typical cheap cheap wild bird feeder into a waterer that will conserve water and require less filling than an open bird bath.
One inch hole saw
Razor knife (optional)
Cheap wild bird feeder
2 liter bottle
One 1/4" screw
One 1" washer
One tube of clear silicone sealant
Step 1: Drill a Hole in the Lid
Find a spot for the bottle neck on the lid. Set it in place and move it around until you get it right. (See the photos for a good idea of the location.)
The hole should be as narrow as possible. The bigger the hole, the more caulk it will take to seal it up. Also, the bigger the hole, the weaker the seal will be.
Put the bottle neck in place, then drill a small hole for the 1/4" screw and washer. (They are used to keep the bottle neck in place. Without their reinforcement, the seal would slip and break from the twisting motion of screwing the cap on and off.)
Step 2: Seal All of the Seams and Holes
Finish caulking all around the inside, between the bottle neck and the lid. Don't be stingy with the caulk. It absolutely must be air tight, or the waterer won't work properly.
Caulk around the bottom of the center pin.
Note the other small holes in the bottom of the feeder tray and caulk them too. (There are small holes in most bird feeder trays, to allow rainwater to drain out of the birdseed.)
Put the lid back on the feeder and caulk all the way around the seam.
Caulk around the outside of the bottle neck on top of the lid.
Put some extra caulk over the screw if it sticks out of the lid.
Caulk around the top of the center pin.
Caulk the holes at the bottom of the feed container on the side opposite the bottle neck. For the waterer to work, you only need to leave the one hole closest to the bottle neck open. (If you have trouble visualizing, tilt the waterer on its side with the bottle neck turned up, as though you were going to fill it. Caulk the holes at the bottom and sides of the feed container in this position, so that you can put in as much water as possible before it overflows.)
Set the waterer in a well-ventilated, out of the way location and be sure to allow the caulk to cure for at least 24 hours undisturbed.
Step 3: Completed Waterer
Tilt the waterer sideways and fill it until it starts to overflow, then screw the cap on tightly before turning it upright.
As long as you have done a good job sealing it completely, the water will remain in place, and the dish will remain full.
You can put the bottle neck on the bottom of the feeder if you want to. Then it will fill easier than this model, but it will be harder to make the bottle neck fit in the space and the seal will have more pressure on it, so it may fail sooner than this one would.