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.)