Why Gods and Goddesses (Devas and Devis) have their own vehicles, mounts or vahanas which comprise various types of animals and birds? Do they have some physical significance?
I think Gods have been assigned their respective animals as vahanas to describe which quality or the ability that they posses. E.g., Surya deva rides on an horse-driven chariot. The qualities of Horse is linked with Surya-deva, i.e., being fast or quick etc., Vishnu has Garuda as his vehicle because Garuda can fly very high and can get a bigger picture of earth. It can also fly great distances which indicates Vishnu deva travels great distances to maintain the world.