Had a call (song) this morning that I have not heard before (16 years of birding in the Midwest), will attempt to describe.
I was walking in the coniferous section of Blue Hill Trail, Sherburne NWR (near Princeton, MN) when a rolling song started about 100 yards to the east (much louder than the Chipping Sparrows and Red-breasted Nuthatches around me). The song continued as the bird (apparently) flew overhead, stopped twice in the woods (again, apparently at the top of the 40+ foot coniferous trees), then proceeded west. The song/call was loud (say, Hairy Woodpecker loud) - rolling - stayed on the same pitch for 3-5 seconds, then would go up or down a half step, calling again on a consistent pitch for another 3-5 seconds. On most occasions (perhaps five minutes of listening), it would do a two pitch call, then cease - although on one occasion I counted four changes up or down (during flight). The song was never slurred. The space between notes was similar to a slower Swamp Sparrow's song, but the notes themselves were similar to - of all things - a Red Squirrel. I received an impression of a medium-sized to larger bird, but never had a visual - and anyone who has listened to a Ruby-crowned Kinglet or Carolina Wren knows how deceptive loudness of calls versus size comparisons can be. Any input (or questions) would be appreciated. Al Schirmacher Princeton, MN Mille Lacs & Sherburne Counties