This is a false argument: It is either (1) comparing apples with oranges or (2) a straw-man argument. Take your pick.
The straw-man you create is that Winged Migration is a documentary about bird migration. It isn't. But, of course, after you've created your straw-man it is easy to compare it to real documentaries and thus you are able to tear it down quite easily. Winged Migration is, as the director stated, a nature adventure story. You might as well compare a travelogue to a documentary - same type of false argument.
Now, if you just stated that you didn't like the movie, that couldn't be argued with.
This movie has touched many people, making them think more about the hardships of migrating birds. Being a bird lover I would think you would appreciate that aspect of this flick.
BTW, I have Attenborough's Life of Birds and it is a very fine documentary.