not all enclosures are the same
not all creatures are the same
but not every living being can be contained.
(in discussing the prohibition of trapping on Shabbat, there is a discussion about different types of enclosures. and whether or not an animal in an enclosed space but can still evade capture can be considered as trapped. But there are some birds that are considered free as even though they are in a house, they don't follow authority and will always evade capture.
for english translation of this talmud page, see here)