I had a mangrove snake that would only eat birds, and the angry monster lived 12 years with no apparent health issues. He came to me fully grown, so I have no idea how old he may have been, being wild caught and all. Only thing I found was that snakes seem to digest birds faster, so I needed to feed more often than if I were feeding rodent prey. Poops were pretty loose as well, but over all they seemed to be nutritionally sound.