Puzzling Canadian woodland bird sound (1 Viewer)

I was visiting a friend with a country property on the weekend, outside the living area it is densely wooded with a mix of white pine and red and white oak (the pine were planted probably 30 years ago, the oak are natural). There is a river a short distance away. My friend drew me a short way into the wood to hear a mysterious single note bird call high up in the trees; it circled around us a fair bit and then the bird withdrew. We didn't have binoculars and anyway I never got to see it, but my friend has (with the naked eye) and he insists it's either a crow or a raven making the sound. He's no birder but he does know that would be unusual for those birds, insists it's a one-off, perhaps from an injury. The sound was quite clear and musical though and while my hearing is not completely keen any more, I'm fairly sure it was neither a saw-whet owl (at least not their regular call) nor a nighthawk (not buzzy enough).

So my question is; what Ontario bird flies high in the trees in daytime, greatly resembles a crow or raven to the untrained naked eye, and gives out a single clear note call rather like a short whistle from a human? I have never encountered this sound before, nor has my friend, who has lived in those woods (as it were) year 'round for well over 2 decades.

Crows and ravens can make a wide variety of sounds. American Crow has a territorial call that seems to match your description.

jmepler said:

Crows and ravens can make a wide variety of sounds. American Crow has a territorial call that seems to match your description.

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That's not quite it, but birds do have regional dialects and it's the best suggestion yet that my friend is correct about the sound's corvid origins. Country legends have it that crows can be taught to talk, like parrots, so no doubt they are versatile.