Joanne,
 
       Tone is key to identifying single-hoot owl calls.  Is this a loud, sharp, and almost downward slurring "WHOO!", like a barred owl?  
        Or is this a low, somewhat drawn-out "Hooot", somewhat soft or muffled?  Is it repeated regularly?  If so.....and I hate to go out on a limb, but what the heck, it could possibly be a Long-eared Owl.  To check your owl calls/tones, try going to Cornell's All About Birds site and listen to a Long-eared call:
http://www.allaboutbirds.org/guide/Long-eared_Owl/sounds
 
Great horneds can also give a single hoot, often very deep and low-toned or muffled, but can also be quite variable.  Try listening to them on the Cornell site to get a sense of their tones.  A single hoot for Great-horned is atypical, but if it's very distant sometimes the preceding notes are inaudible, and all you will hear is the last note.
 
Habitat and location could also be clues to ID;  is this is broad-leaf forest? If so, then likely Barred.  If coming from a suburban/rural conifer thicket or bamboo-type dense thicket, then possibly a Long-eared.  If in mature pines, then most likely Great-horned.
 
Ross

--- On Thu, 9/23/10, Joanne Howl <> wrote:


From: Joanne Howl <>
Subject: [MDOSPREY] Single hoot
To: 
Date: Thursday, September 23, 2010, 12:42 AM


Several times in the last two weeks I have heard an owl call - but just a single hoot.  At least twice it has been near my home, where Barred Owls are common and Great Horned Owls will occaisionally call.  But I've heard this in at least one other place in AA county recently - can't remember where at the moment.   

Anyone have words of wisdom on how to figure out what owl is calling, when all you get is one hoot?

Joanne

Joanne Howl, DVM

West River, MD