No help to Op, but it remiinds me of a pigeon we had at work in one of the very tall ceiling'd buildings.
It got in, we couldnt reach 20 ft to the ceiling to catch it, we left the very large doors open for days to see if it'd make its own way out. It just sat there on the pipework up there.
After about 2 days we started to worry for it, there was nothing for it to eat.
This is where logic comes in...although we hadnt thought of it. Our boss came in after a few days off, he knew nothing about it of course.
'Just throw a bucket of water on the concrete floor by the big door'...'they can do without food for a while, but water will definately attract it'
We did so, left the building for 10 minutes....came back, it'd gone
I was going to suggest that
...honest.