From personal experience the Great Blue Heron makes a sound like eeyao the y and following sounds being nasal and quick. I suppose it could be perceived as Frank. Source: personal experience.
Jul 24 2012, 4:13 PM
Baloo55th
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Baloo55th 22 year member
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The Grey Herons found near (about 3/4 mile) Chez Baloo have the call 'frank'. They're the ones I associate this call with although, not having any Blue Herons of any size around here, I wouldn't comment about the other suggestions.