I've seen some done with tiles or broken tiles that were just beautiful. Check the mosaics forum.

This is what my Mom did with her old birdbath.{{gwi:1988}}

Wow! That's really gorgeous!

I was checking out this forum, looking for ideas on building shelving or something similar for some potted plants... and since I love birdbaths... I had to check out this post...

I agree with the other suggestion... mosaics would be really pretty, and doing so might just take care of the crack, too. As you are tiling, you could silicone the crack, and tile over that... it might take care of any water leak.

Although... the planted birdbath in the photo is awesome! That's a great idea if you didn't want to go through the trouble of patching or tiling...

I would think with today's products available at home centers, you could find some type of paint or stain or something made specifically for concrete. If there exists such a thing, you could stain or paint your birdbath, and at the same time, repair any cracks or leaks.

If you can't repair the leak, perhaps you could find some type of container or plastic barrier to line it with.

Just a few thoughts... :-)