Thank you! This all makes sense.

Yes, both sentences are correct. But the one the answer key gives retains the grammatical structure of the example by putting ''viele Vögel'' at the end of the sentence rather than at the beginning. By putting ''viele Vögel'' at the beginning of the (written) sentence you also put emphasis on the fact that there are many birds whereas the answer key emphasises the forest. In spoken language it would seem(to me that is) that you would almost always use the one from the answer key and emphasise certain parts of the sentence by changing the intonation of the respective words. Also the context of those sentences is crucial. If for example there were questions like: ''Was fliegt über dem Wald?'' or ''Wo fliegen viele Vögel?'' then you would put the answer to these questions at the beginning of your answer. So in my example that would mean: ''Was...?'' - ''Viele Vögel...'' and ''Wo...?'' - ''Über dem Wald...'' respectively. I hope that helps out.

Generally, yes. But in the given sentence the "forest" is the reference word. It's all about the forest, not the birds. So your order is not right. The time form you have chosen is correct. The answer key ist correct. regards....

Either one is correct.