Amanda and I also heard a single hoot from an owl while camping at Tuckahoe SP a couple of weeks ago. We heard Barred at a different spot in the park around dusk. The single hoot came in the middle of the night and was not the typical call of any of the owls.  It was quite close and only making the one note, not a distant muffled sound, and not downslurred. It was not a Barred. I considered Long-eared as well but it was giving one note every 2 - 4 minutes not every 2 - 4 seconds like the typical Long-eared call. It sounded like a Great Horned to me but it was only doing the first long hoot of the typical series "hoo hoo hoo HOOT hoot." It was somewhat drawn out (lasted about 1 full second). I had never heard this vocalization even though I did owl surveys for a few years as an undergrad and then as an Audubon volunteer. These were all in the winter / spring, however. I wonder if Great Horned gives a different or abbreviated call in late summer / fall? Not sure if Long-eared ever gives a single hoot? Habitat was mixed deciduous / coniferous with adjacent open areas which would be fine for Great Horned. 
 
Cheers,
 
Frank Marenghi
Annapolis, MD