What changes the supplies answer
Choose a carrier the bird cannot chew open, slip out of, overheat in, or slide around inside.
Size matters
The bird should be able to stand naturally, turn, and stay stable without being tossed around in a huge empty box.
Footing matters
Use a safe perch only if the bird can balance during travel; otherwise towel or paper footing may be safer for some birds.
Train before stress
Let the bird see and enter the carrier on normal days so vet trips are not the only carrier experience.
Best carrier
Secure, simple, ventilated, washable, and familiar.