Bantam chicks can get through the grate openings in those airline crate doors. I use a couple of rows of duct tape to keep them inside with mama.
Another awful lesson learned!
Mary
I lost chicks, and had their mama torn up but alive, in the morning years ago. They were in a smaller airline crate, and pulled through the front cage grating by raccoons. Awful! After that, I use a very large airline crate at least, and in the safe coop at night.
Mary