It has an ID number on it that identifies the breeder and probably the clutch the bird came from.
I assume you mean indoor, pet birds. Cover their cage with a cloth that does not let light in.
you can get worms from pet birds
No, you do not typically have to get shots for birds.
yes,but other pet birds don't fly far
If you are talking about wild birds, then none of them are truly mean. Although some of the things birds do are considered mean, or even cruel in our eyes, in reality it is what the bird needs to do to survive. However, if you are talking about pet birds, it's a different story. Pet birds are never mean, with the exception of a major flub on the part of the person that raised them. If a breeder/raiser was not sure of what they were doing, or something happened to the bird when it was still young, or it wasn't introduced to strangers at a young age, then it could have the potential to be very mean.
aviary
birds
cage
There is no scientific evidence to prove that using a camera flash when photographic pet birds is harmful.
I actually have a pet mouse and have taken it on a walk with a rubber bracelet and some yarn and it went just fine.
birds
A cage with a perch.