What kind of bat did we see/hear while camping near Flagstaff, AZ?

Hi Fluther! Been a while!

This summer my boyfriend and I were camping at Sunset Crater, Arizona, just north of Flagstaff. It’s a real weird volcanic area with black sand dunes, lava rock everywhere, and calderas peppering the landscape if you could see it from above. So we were camping on National Forest land just literally outside the park boundary and as soon as it got dark we started hearing this noise—in terms of animals I thought at first it was either a bear, or a cow or moose or something. It was a deep bellow. Then, thinking that unlikely probably just to comfort myself, I thought oh! Maybe it’s an owl! I know owls can make crazy noises and the sound didn’t seem to be moving much. It would happen every couple minutes maybe. We ignored it figuring it was an owl.

Well, when it got dark it became louder and more frequent. Curiosity was getting the best of us and plus the moon was bright so we went for a walk and took our headlamps. We could tell we were getting closer to the noise and also we could hear a bird/bat flying around above us and chirping. It turned out to be a bat, obviously, several times it flew quite close to us. It was pretty big. But this sound it was making was not the usual bat sound, that little chirping that it regularly does. Every 20 or 30 chirps it made this OTHER sound, the sound we had been hearing. Like a deep, hollow burp! Or a gong or something loud and ridiculous! I have NO IDEA what type of bat could make a “noise” like this but i am DYING to know. This was a month ago and I have tried to google crazy bat sounds but nothing has successfully come up that has helped me figure it out at all!

If you have any idea what this could be I would LOVE to know especially if youve heard it before too! I am real intrigued.

Thanks :)