According to my National Geographic field guide of North American birds, the Western meadowlark’s song is a “variable series of bubbling, flutelike notes”, while the Eastern meadowlark’s is a “clear, whistled see-you see-yeeer”. However, the ranges overlap in North Dakota, so I’m not sure which species you were seeing there.
We only have species of robin commonly found in North America, but the song does vary by location, and seems to be set by adulthood. Also robins, like most songbirds, have a “call” which is quite different from their “song”.
As he succeeds, he takes no credit. And it is just for that reason that credit never leaves him.
– Lao Tzu, Tao Teh Ching