You need to take your bird to an avian vet ASAP. Either put your bird in a smaller cage with low perches or move the perches down in the cage it is in. Provide food and water near the low perches. Keep the bird warm until you get to the vet by covering three sides and top of the cage.
If you do not have an avian vet, you can look for one on our Find an Avian Vet page.