Different and Delicate

I've been to many zoos with free-ranging guineafowl over the years, but they've always been the domesticated form of the helmeted species, never the vulturine guineafowl or crested guineafowl, the other two species that you see in American zoos.  Likewise, I've been to dozens of zoos with free-ranging peafowl, but always of the Indian, or blue, species.   I've never seen free-roaming green peafowl.

I'd wondered about that for a while.  Was it a question that some species were more delicate than others and required more direct, controlled care to thrive, whereas other species were hardier and could be let loose, with a reasonable amount of confidence that they could handle themselves?  Or was it a matter of economics, that some species were considered to valuable (either for financial cost or for conservation status) to subject to the risks of a free-roaming life, be it a great-horned owl or a tram driver who isn't watching where they are going, and must be kept safe?  

I suppose part of it also came down to another question.  Is being free-ranging the ideal?  In a perfect world, would the zoo be allowing all animals to run free on grounds, locking up only those that were deemed necessary for safety or animal welfare?  All of the room to roam, the diverse habitats around the zoo, the constant variety, the exercise, etc.  Or is it a less-than-ideal living situation, animals being risked for the purposes of a better guest experience, in which case those blue peafowl and helmeted guineas are starting to look a little... well... disposable?

It looks like there isn't a completely clean answer.  Yes, some species are more delicate than others.  Green peafowl are considerably less cold-tolerant than blue peafowl, and catching up a bunch of free-ranging, flighted birds every fall could be very stressful, but necessary if no one is to be left out during a freeze.  They are also more endangered than the blues.  Vulturines are similarly more delicate than helmeteds, less tolerant of damp conditions.  The debate about the benefits versus costs of allowing other species to roam free is ongoing, though I do feel that more zoos are moving towards bringing their formerly-free birds into aviaries, or de-accessioning them altogether, than the other way around.