UPDATE
I went on youtube this morning to listen to more fox/coyote vocalizations.
I clicked on a post with eerie night sounds and that was exactly what I'd heard on 2 occasions.
I was horrified when a viewer identified the sounds as those made by a rabbit being eaten! There are some rabbits in the neighborhood and I'm assuming a raccoon got them as they ate fallen birdseed. I hate that coons eat their prey alive, I don't want any animal to suffer.
Well, thanks to all for your advice and insight. I appreciate you taking the time to help solve this mystery. I'll be sure to lock my hens up securely every night!
Carrie Lynn