I have a question: would "birds of prey are birds that hunt" with plural "birds" also be an acceptable translation, as Klingon nouns aren't necessarily marked for plural? couldn't toQ be "bird of prey" or "birds of prey"? Or does 'oH necessarily make toQ singular?
Yes. While the noun itself does not indicate whether you are talking about one bird or multiple birds, 'oH can only be used for one bird. It would have to be bIH to translate toQ as "birds". On the other hand, this kind of equivalent can be used to state a fact which is generally true and so, even though, we are talking about one bird, you are expected to extrapolate that to all birds. In a way that English sentence you wrote is used to express the same thing that this Klingon sentence expresses, but we don't allow it as a translation since we want to make sure you have taken notice of the effect that the 'oH has.