My conception of spirit animals is that everyone has a companion spirit animal that resides in their body. Many people have more than one spirit animal and they keep their spirit animals in the corral. Most people are totally unaware of their spirit animals.
It is a custom to acquire a body part of your spirit animals if possible. A picture or some other token can be used as an icon to call forth your spirit animal. All of the body parts and/or icons are kept in a wooden box hidden in a secret location. When you wish to call forth your spirit animal for some form of nocturnal work you remove its body part and/or icon from the box and place it on your altar/holy table. You will travel through the astral plane in the form of your spirit animal to perform the work or mission you wish to accomplish. Insects, mythological creatures, and extinct creatures like dinosaurs can also be part of your corral.
Your spirit animal can be revealed through dreams, visions, meditations, or frequent encounters with said creature. You can also choose a spirit animal if you feel drawn to a particular creature. Obtain your body part and/or icon of the creature and place it on your altar/holy table. While resting in your bed envision yourself becoming this creature. Most often your spirit animal will reveal itself in dreams. In rare occasions you will be consciously aware of the spirit of your spirit animal entering your body, usually through your back.
It is wise not to reveal your spirit animals to other persons. A powerful form of psychic attack is to attack a person's spirit animal which will have a direct effect on that person's welfare and well being.
A funny story happened to me involving one of my naguals, the Ancient Aztec name for your spirit animal. Completely unconceived by me, one day while at work, a spirit animal entered my body. I saw it happen with my minds eye. My thoughts where totally mundane at the time of the occurrence. Immediately I received a phone call from somebody very close to me and they inquired if I was alright. I assured them I was fine and went about my daily duties. The next day a mother and her young child walked by me. The young child looked at me and called the name of the spirit animal that had entered my body the day before. The mother was surprised and said her child must have been watching a show on television which featured this animal.