The proper behavior of humans toward animals is a middle way between human superiority, which allows humans to do whatever they please to animals, and views requiring humans not to interfere with animals at all. Since ethics is principles for social cooperation, only a restricted class of animals—work animals and pets—can have ethical standing. In any case, eco-ethics requires us to treat animals humanely and not as objects.
TopBuddhism
Buddhism is not a theistic religion. The Buddha himself thought that the existence of suffering showed that there was no omnipotent, loving God in charge of the universe. From the beginning Buddhism seems to have been concerned to stay within the realm of the natural rather than the supernatural. Thus, there is an emphasis on karma, or cause and effect, rather than supernatural emanations. And it was the Buddha himself who promulgated the doctrine of no-soul (anatman). This is the doctrine that there is no permanent human self, only a stream of experiences.
However, the doctrine of no-soul seems to conflict with another Buddhist doctrine, the doctrine of reincarnation. If every sentient being is re-born as another sentient being with somehow the same identity, each sentient being harbors something permanent enough to survive death. Buddhists call these semi-permanent carryovers, seeds. Many Buddhists are not bothered by this seeming inconsistency, but some are. Although I am not a Buddhist, it bothers me1 (Buddhists generally do not strive for uniformity of doctrine.).
Buddhist reincarnation as a way of survival after death has distinct advantages over the afterlife of Christianity and similar religions. Buddhist reincarnation requires no extra supernatural realm to house survivors after death.2 Also, since reincarnated people return to this world, there is every reason to preserve and improve this world. In addition, Buddhism requires no fantastic stories such as Jesus and Mary ascending into Heaven. Perhaps those stories did not seem fantastic when people believed in a three-story universe, with Heaven in the sky, mortals living on earth’s surface, and death and hell underground. But as soon as people realized the earth was round and that breathable air rapidly ran out as one ascended, the ascension of Jesus and Mary seems preposterous. It would be consistent if Jesus, being God, needed no oxygen mask, but Mary would not have been so fortunate. Also, when Christians restrict the Afterlife to human beings, they affirm a very strong form of unjustified human superiority. Why can’t whales go to heaven as well?
Buddhists have respect for all sentient beings. This entails not killing sentient beings and not eating them. One of the forbidden occupations in Buddhism is that of butcher. Respect for all sentient beings is the aspect of Buddhism of most of interest for our current topic of human/animal relations.