Without even getting to the question about how one would define these characteristics, we are forced to look at examples of humans who most people would consider are less rational or less intelligent than most normal animals. The two most obvious examples are human infants and seriously retarded humans. It does mean however, that these two criteria are morally insufficient to justify superiority. So, there needs to be some characteristic aside from rationality or intelligence that would set humans above other animals. When we examine most of the other reasons that are generally offered, we find that they too are fallacious.
All animals have the same interest in avoiding pain and death.
In other words, if an individual can suffer, we have a moral obligation to do what we can to avoid inflicting suffering unto him or her. As humans and other animals are not exactly the same, it makes sense that we should not have the same exact rights. For example, all humans should have the right to vote. However, animals are incapable of understanding the concept of democracy or voting and therefore do not need this right. Similarly, fowl have a strong biological need to flap their wings and fly, whereas humans do not.