You can google info on galah/'too hybrids. But I'll try to pick out relevant data for hybridization. It's not all about parrots.
hybrid vigor:
http://www.ncbi.nlm.nih.gov/entrez/quer ... t=Abstract
pdf file/ hybrids are common:
http://www.americanbirding.org/pubs/bir ... 4to235.pdf
Longfeather origin theories; skip to hybridization section of you're in a rush... at times this writer refers to hybrid in the sense of two lines within a species crossing, which speaking in genetics is possible considering when you keep a group isolated the genes do change:
http://users.accesscomm.ca/parrot/articles/LFT.htm
heterosis is another term for hybrid vigor
Most of the good info on hybrid vigor in avians is found in books. Not too much online.
Now I wonder if perhaps hybridization is normal. The species we know now are productions from hybrid pairings in the past creating a stable base for a new species to breed with itself. So what if hybrids now are simply a continuance of this?
Speaking in terms of in the wild, since hybridization is so common in wild avians.
Today people have an obsession with keeping everything "pure" and old things the same. In the old days, when the water got too high in Venice, they would knock the buildings down and build on top of the old, making them higher. But today it's too "historic" and so it's sinks into oblivion.
If we keep trying to make things pure and preserve everything, would that be going against nature and would we eventually lose what we were trying to save?