This idea came to me as I was thinking of genetic experimentation and how it's incredibly hit-or-miss, and even the smallest variants -like, say, breeding a chicken that lays a lot of eggs- usually take generations to successfully make.
So... where are the rest of the Avian-hybrids?
This quickly evolved into an AU where Itex is a government company trying to make supersoldiers. They've been experimenting for decades now, but every hybrid either dies in adolescence or has so many defects as to be useless. The Flock is pretty much their last hope before they run out of funding and have to shut down.
The place where the Flovk lives after Jeb "rescues" them is actually a vast testing facility where Itex monitors the Flock's fighting skills in a controlled environment and so on and so forth. It's fine, everything is going great (for Itex), until-
The Flock escapes. Not only does the Flock escape, they escape about two weeks before Itex planned to officially call the Angel Experiment a success and present/sell them to the military.
Enter Double-Oh-Seven, AKA Tyto Recall. A freak accident from the early stages of experimentation who somehow managed to survive, though not without a heaping of health issues. They've been "in charge" of monitoring the Flock for the past four years. So, Itex, being on a bit of a time crunch, puts them on the Erasersquad(TM) assigned to find the Flock and bring them back.
Oh, did I mention Tyto is the one who taught Max and Fang how to fly?