May I just suggest that I think you'll find that hearing aids will definitely improve your ability to hear bird calls! That's one of the first thing I notice when I'm out wearing them walking around, along with the sound of rustling leaves. You'll certainly appreciate that. I say this as a long-time, but casual, birder myself.
I was curious about that goldcrest you mentioned, since I don't think we have them in Southern California, so found a 'tube video of one singing (they certainly are adorable!)
It was a little hard to hear without my aid (only have one now, ha!), but after inserting it I could hear it quite plainly (yes, very high-pitched).
So even though audiologists are really concentrating on speech comprehension, I think you'll find your aids helpful with sounds other than speech.
Just for fun/curiosity's sake, you might like to play with tone generators such as one I found here"
tinnitus test
You can play with that to see just how high (or low) you actually CAN hear.
Best of luck; keep us posted.