Since bats were only seen at night, they were once considered the souls of sleeping individuals. That's why I guess we also relate them to vampires, they only come out at night. Many bat species dwell in caves therefore people considered them to have something to do with the Underworld and death.
In my post Trick or Treat I have noted that Halloween was thought as the beginning of the cruel winter, which was associated with death. So it is logical that an animal related to be of the Underworld also be related with Halloween.
Just like bats, most owls move around at night. If you've heard an owl, you can imagine what you would feel like listening to that sound in the night, especially for those that didn't know what it was, or how big it was. Many thought it was the sound of a demon or a lost soul. And even if someone did see the owl, that instantaneous twist of the head they do can be scary with those big eyes! I remember when I saw an owl do that to me in the London zoo many years ago, I announced that owls are the Gods of the Birds! I was only 5 :)
|Owl Sandwich Pop|