This is a warbler-smaller than a sparrow but try BirdJam (just Google it) & see if Black Throated Green Warbler might be it. It supposedly sounds like zee-zee-zee-zoo-zee or see-see-see-say-see. I can't think of anything else with that cadence. BirdJam is helpful but after I listen to a few I get mixed up. Susan

Nope, the who in a great horned is a distinctive who with a deep tonal quality. This was definitely more of a child's slide whistle quality, more of a toot. I'm thinking it was a northern saw-whet as it most closely matches that tonal quality. Here is a link that might be useful: Listen to

They are indeed beautiful, catherinet. That last note might really be a cheet. That's probably what threw you off! ;) Regarding writing out bird calls, I wonder who decided the Barred Owl says "Who cooks for you, who cooks for you". Even though I'm in Iowa, I sometimes hear a Barred Owl with a southern accent. I hear "Who cooks for you, who cooks for you all!"

There are half a dozen subspecies of American robin. The ones from Newfoundland are sometimes called "black-backed robins", and in addition to being much darker than the more common subspecies are somewhat larger. Birds from the rain forests of the pacific Northwest are also very dark. Probably what you saw was an adult male bird from one of those subspecies.