For us, there’s something very relaxing about the sound of moving water—think of the burbling of a stream, rain tapping on the roof, ocean waves gently lapping at the shore. Birds, on the other hand, get excited about it. So, if your birdbath is quiet, break its silence, and you’ll turn it into a bird magnet—they’ll find it irresistible and you’ll see a lot more activity (this is true for any water feature). There are several appliances that will make water move.
Bubbler
The job of a bubbler is to roil water so that it’ll produce bubbles. They’re typically solar powered and there are many different styles, from plain to elaborate.
Water agitator
Set one of these in the center of your birdbath to produce continuous, gentle ripples. Available as solar-powered or with batteries.
Dripper
The sound of dripping water attracts birds. The dripper must be connected to a water source, of course, usually a garden hose. (You can find ideas for do-it-yourself drippers made from plastic bottles, but keep in mind that plastic is toxic—current research is suggesting that even BPA-free plastics may be unsafe. )
Mister
This does just what its name says. If you can position it so your birdbath will catch falling droplets and nearby foliage also gets wet, well, the birds will be very happy campers, er, bathers that is! Some will bathe in the drips and ripples in the birdbath, some will bathe in the mist and others will bathe in the wet leaves.
Fountains, water features
A fountain or water feature is a good alternative to a birdbath. If you want the birds to bathe, there must be a shallow area for doing that. Most birds bathe in water only 1/2- to 2 inches (13–51 mm) deep.
*NatJLN / Wiki; cc by 2.0
More reading:
Provide water for wildlife
How to attract birds to your yard
No spring in the step of hungry spring birds
Assortment of bubblers and agitators at Amazon