My window planter box family of Juncos:

http://ustre.am/1oMrC

This is on the top floor in a 3 story light-well with anti-pigeon mesh above. I’m greatly concerned about what to do when the babies start fledging.

If they managed to survive going almost straight down 3.5 floors onto concrete, there’s no way they’d be able to fly straight up to get out. I’m open to any suggestions you might have to insure their survival.