Mutation
Whipper's vet declared him as a mutant. Bird mutations are well documented and can cause health problems.
Mutation is common within the species, caused by "budgerigar colour genetics". However, Whipper's unique mutation is long curly feathers, short flightless wings and apparent blindness. It is suspected that the mutation, which is known to Budgerigar breeders as the "feather duster" mutation, caused unrestricted feather growth, resulting in the budgerigar's dishevelled appearance.
Read more about this topic: Whipper (budgerigar)