Contrary to popular thoughts, most owl species don’t simply “hoot”, if at all.  Burrowing Owls have many types of vocalizations used in different situations.  Some are for advertising their territory, sounding an alarm or, announcing a warning.  The warning call is an awesome imitation of a rattlesnake’s “buzzzz”, which shares burrows with these owls.  A predatory mammal going down a dark hole after a little owl will think twice about continuing.  Listen to these examples from the great online library of xeno-canto.

Advertising “Song”
(http://www.xeno-canto.org/104661)

Alarm Call
(http://www.xeno-canto.org/104662)