A 'Self' in Buddhist thinking consists of Form, Sensation, Perception, Will, and Awareness. It seems like individual members of other animal species have the 'ingredients' for a Self. Does this mean that they can realize Nirvana?
Nirvana is the immersion of the manifest image of self/ego into the formlessness of consciousness. The formlessness being more than emptiness or nothingness it is potential and energy that is intelligent and omnipresent. Man has the capability to realize ones self as both formless and form at the same time, and can merge the individual consciousness with the omnipresent consciousness to realize itself as One consciousness.
Form is a projected thought, congealed energy that is the creation of potential in action, also known as God.
Tho the animals are connected to this source it is only man who can make choices to evolve or devolve from form to formless or from formless into form consciously. Animals do not have an ego such as man does to take pride in him/herself or the capability to plot against his own species. They don't harbor hatred or contempt, nor do they make martyrs of themselves in the beliefs of spiritual theisms. Only man can stretch himself from the depths of stupidity and ignorance to the heights of God awareness and back again by making choices to effect these experiences.