Firstly, why should animals be caged in the first place? They are wild and uncivilized creatures. They have very narrow aims; eat, sleep, breed , die. They are potentially a threat to humans as there are countless recorded incidents of wild bears roaming into human settlements and going on a rampage, killing young children in search of food, one could question this by considering the fact that humans were the first to intrude into their territory, for natural resources or commercial benefits.
Animals are also prone to cause numerous diseases as they often get poisoned by human waste, particularly industrial effluent, The general population which is affected by these diseases would prefer to have these animals slain, rather than caged. The most dominant reason for caging animals or birds is for personal entertainment, whether it is a lion in a circus forced to jump through loops or if it is a macaw kept in a cage as a pet or "companion". Pet owners can argue that they love the pets they keep as a part of their family, they provide them with food and shelter, something far better than that which they could have ever seen in the wild. Medical attention is provided and ample enjoyment to accompany that "perfect" life, The pet technically lives like a king. research also accounts to animals being caged along with education of the youth through zoos, what education could a zoo provide if the animal is far from its natural habitat?, the only knowledge a child could squeeze out of a zoo is that monkeys like to throw things and they also like shout an awful lot at observers.
Why should the animals be allowed to live in the wild? without a cage and unsupervised? simply put, animals are also living creatures with souls, they also feel