In neoshamanic literature this spirit has different names. To mention a view: totem, nagual, poweranimal, protection spirit/angel/animal, fylgia, clan spirit, animal soul, alter ego. These names describe this spirit in the non ordinary reality in different paradigmas.
There is a difference between the personal and collective tiergeist. Your own tiergeist can only be achieved by your own efforts. Collective spirits can be achieved on many different ways, for example astrologic methods (see Sun Bear) or via family traditions or tribal inheritance. Collective animal spirits are representing whole groups of persons, be they shamans or not. In magic orders this „animal spirit" is the egregore.
Generally speaking, everyone does possess a tiergeist. Actually the shamanic practitioners are the only ones working with it and knowing it.
There are no guidelines, how many tiergeists you may possess or how they may appear, whether they are everytime present or being absent for some days, making holidays (and drinking a cup of really hot coffee in a bar somewhere in the spirits world). Abilities, personality and demeanour are individual to each tiergeist, too. Disappeared tiergeists can be brought back in shamanic journeys. The tiergeist often listens to your true will and does realize this will. The better your contact, the more often and intense these realization will be.
Akin to the tiergeist is the holy guardian angel of Aleister Crowley or Abramelin the Mage. Labeling such spirits as „helping spirit", as it was done by certain anthropologists and wannabe shamans, should be reflected.
Helping spirits are a different class of spirits. They possess a kind of temporal agreement with the shaman and are specialists. The relationship is on a purely professional base. As mentioned above, the tiergeist is much more a friend and companion in the spirits world (by the way: In some tribes in siberia shamans had an official relationship to their teirgeists).
Shamans often possess some helping spirits and bind them at material bases, as well. The tiergeist can be compared with the animal kings of some tellings. Tiergeists are not individual, once living, spirits from the animal but it represents the blueprint or archetype of any individual of the animal.
The term poweranimal or tiergeist implies a spirit of animal like appearance. My former theory is obselete, that there are NO rules about the appearance and kind of the animals, functioning as tiergeists. In central
The tiergeist can change its appearance and adapt to any environment. Eagles that can dive and swin in the ground or in the sea, or elephants flying around are not unheard of. During shamanic journey shamanic practitioners occasionally are merging with their tiergeist, the astral image then is looking like the tiergeist or a hybrid form (just think of egypt´s deities to get an idea of the appearance).
Deep contact to the tiergeist can have amazing effects in normal life and reality. Animals can feel the presence of it and react according to their instincts. Conscious calling of the tiergeist and invocation can have subconscious effects on humans, too. (www.kondor.de)