Ive read quite a few things about Macaw subspecies and I think whether or not they are officially a subspecies isnt so important and more to do with taxonomic technicalities. The difference does exist. Apparantly they are actually from Bolivia too. I think that this "subspecies" or abberant or whatever you want to call it definitely does have slight genetic difference, like whatever gene determines size, and I would assume they came about from a selective breeding "survival of the fittest" situation. B&Gs in this region may have been isolated and for whatever reason the bigger birds more successfully survived and reproduced, allowing the "big" gene to be passed on and common in this area. Over time, and with the big birds having the most success, they would eventually become the norm in that area. Whether or not that means it is a subspecies or not would come down to what is required to be a true subspecies and if they fit that category. Continual breeding of large birds would produce a bloodline of large birds. If they are not a true subspecies, it may however be a good example and living representation of *how* subspecies form through gradual evolution via selective breeding.. once they pass a line genetically where there are distinctive differences, they can be official. Just my speculation.
Edit:forgot to mention, theres another disputed sub species known as the giant greenwing, which can be as large or larger than a hyacinth. Its possible the same theory goes for that as well.
Hopefully one of our Mac people will be able to help.
