I have had a pair of finches (red/brown male/female) thast have been doing the same thing for 9 months.
I expected it to stop at the begining of summer, but they haven't. Nice wake up call at sunrise. Thump...thump...thump... thump... you get the idea.
The solution is to make the glass non-reflective or hang something on the outside so the birds will stop "defending" their territory from the other bird.
Got so used to it, it doesn't even bother me. I always have to warn my guests when they are sleeping in that room, that they will get a wake up call in the morning.