How do you know if a birds wing is broken?

If a bird has a broken wing it will most likely be seen on the ground and climbing trees. It climbs to a mid portion of the tree to get away from ground predators and hawks that may make a tasty meal out of the bird.

Now if this is your pet bird i suggest taking him/her out of the cage and gently, gently toss him in the air to see if him/her takes flight. If the bird tumbles out of the air it is most likely the bird does have a broken wing. And i suggest tossing the bird towards something like a bed for a soft landing if he/she tumbles.