The tag alias #67885 birdbath -> bird_bath is pending approval.
Reason: Or the other way around.
Topic: Tag alias: Birdbath -> Bird_bath
Posted under Tag Alias and Implication Suggestions
The other way around would be best but you're absolutely correct that it needs to be done.
+1 to flip the alias
Also agreeing on the alias flip
Google Trends shows that people seem to prefer "bird bath", and I'd tend to lean towards that too, but it looks like both forms are equally acceptable so I don't care which way it goes around.
Dictionaries do seem to prefer birdbath but I'd assume that has something to do with the fact that's a word and bird bath is two words.
Wikipedia says "A bird bath (or birdbath) is an artificial puddle or small shallow pond..."