Planting for birds

I've made a start on clearing out a corner that's all brambles. I'm about half clear and I've spotted a blackbird nest in the hit I was about to do, so I've put some back and left it alone.

I've still got to get that corner clear though once they're fledged, so for next year I'd like to make provision elsewhere for them.

I've got 50ft stretch running alongside my garages that I don't do much with, and the fence there needs some extra support as it gets hit directly with the spring and autumn winds and it did start leaning last time after that run of strong storms. Reinforcing that is first on the list but after that, what could I plant in there that would do the job?

The stretch is 6ft wide at one end, narrowing to 4ft at the other. It gets full sun about half the day. Whatever I put in doesn't want to get huge or take over, because pruning will be very difficult as it gets mature.

So I'm thinking 8-10ft max height, and not vigorous enough that it's going to compromise the fence. And needs to be relatively dense to support potential nests. Maybe some forsythia or ceonathus might work?