They need to dry to their wings for several hours before you release them. Wait at least 3 hours. Normal behavior when they are ready to go is that they will drop down to the bottom of the cage and start fapping their wings. But, if you distrub them that can also make them drop down. Make sure it has been several hours before you let them go. It's a tough world out there and they have to be ready to evade predators.
Herndon, VA (USA)
Take care of the small things....