For example, hummingbirds would never wade into the bath like other birds, because they bathe only in flight. But I have watched hummers zipping back and forth through the drips, timing their flights so that they catch a water drop on their backs on each pass. There are many ways to arrange for a drip. If you like an elegant-looking birdbath, you can even purchase one that has a dripper built in , as shown at right. Birds don't want to lose their footing, and they will hesitate to use a bath with a glazed, slippery bottom.
Cement is good.
Not where cats can hide. Cats like to lie in wait beneath shrubbery or behind a concealing object and then pounce on the birds when they're wet and can't fly well. So put your birdbath at least five to ten feet from such hiding places. Give the birds a chance to see the cat coming. With an escape route.