i heard that avian tribes are cowards and will fly away leaving their fledglings could someone abduct said fledglings and raise them to be mailmen in their kingdom?
No, in fact the "groundlings" (ie: the young too young to fly) are pretty much the only time an avian will stand and fight. It's basically the only reason they have warriors in the first place is to defend their young. And they have a deal with gargoyles since they tend to setup their aeries in places where gargoyles live.