My DH makes concrete birdbaths for a living, and I often paint them with great success using ANY kind of paint. Spray paint is usually the most cost effective, and provides a good base coat. I use acrylic paints that can be found in craft stores for accents or highlighting. I also use clear spray paint to seal the paint.

Hint...make sure the birdbath is very dry before painting. First wash it down, then let it dry. If it's raw concrete, there will be lime leaching and some manufacturers already paint the piece with a mixture of paint and cement to cover any pin holes or patch marks.

You don't need to primer the piece...concrete is the easiest medium to paint on. Let the paint dry very well between coats, then apply at least 4 coats of clear spray paint as the sealer, particularly in the bowl.

Most spray paints today are non-toxic. They're not going to leach anything bad. Frankly, in my opinion, I've seen birds bathing in puddles on the street that have a shimmer of motor oil in them. I've never seen any adverse reactions to the spray paint I use.

Most commercial manufacturers use these same types of materials to paint their pieces. Patio paint is expensive and you will need a lot. Krylon or other premium spray paints are recommended. Don't use ANYTHING that is petroleum or oil based! (Like Thompsons Water Seal).