What is the symbolism of a sparrow or small bird as an animal or spirit guide?

The bird or animal is not itself a spirit guide, rather an entity not currently incarned or a spirit if you will is capable of temporarily putting their attention into an animal or bird for the purpose of getting your attention. Many times one who has recently departed the physical existence will choose this method of saying goodbye and to say that all is well. Another example would be a dog who seemed to miraculously go to find help for an injured person. There are many stories to verify this. Another way to identify guides is guardian angels. In addition to this explanation- a bird represents suconscious thoughts in motion if it if flying. If it becomes an animal it will represent conscious habitual thinking or action without thought, just using previous information without current consideration. ANSWER The bird is not usually a spirit guide in the beginning of a trance experience but winged avian creatures are part of the transformation that occurs in the second half of a shamanic trance experience, sometimes a bat, sometimes a winged serpent, perhaps angels are the same as these images. The bird itself is usually at the top of the world tree at the summit of the flight upward. I often wonder if the shamanic trance experience was split into the different creatures of demons, angels and god roughly corresponding to spirit guides and serpents, winged avian transformed creatures, and the bird atop the world tree. So we may have an evolution of a process of images that over time gets split apart into different mythical elements, with distinct normative value judgements attached to them.