I think that a spirit animal kind of adopts you. Sometimes they stick around, and become almost an alter ego. But sometimes they can make themselves known for a short while, because we need to learn something and they have agreed to teach us. A shamanistic view of this would be that you are using the spirit animal magic, to bolster some quality that you lack but they have in abundance, for example.
Many of the old folklore stories from all over the world have surprisingly similar themes and attributes given to spiders, say, or foxes. Ancient stories and poetry have many layers of meaning, and dreams and visions are how our subconscious mind interprets and makes connections the conscious self might miss.
The little stranger that had been aheming discreetly for my attention is a wren. Actually, I was told this many years ago by one of the coven elders, but unfortunately we were both a bit tiddly-p*ssed at the time and I had forgotten. It took lockdown, of all things, for the wren to start chirping at me, reminding me to be bold, and speak out when needed.