There has been some excellent dialogue on the identity of the heard bird on the Aitkin field trip Saturday.
The bird sang repeatedly for a couple of minutes, then shut down. The song could easily be transliterated as "Peter, Peter, Peter", but with an occasional two note ending as well, and much more musical than Tufted Titmice that I've historically heard in southern Wisconsin over the years (former residence). It was very loud/emphatic. About half the group joined searched visually for the bird, but we were hampered by the ponds and under/overgrowth. We did glimpse furtive movement around a cavity, but never had anything like definite views (as noted in the original email). We came to the conclusion that the closest song was a Carolina Wren after playing a CD - believe it was the second or third set of calls on Stokes (?) that was a match - one person noted a short response from the bird while playing it. Today I read an equally plausible audio ID: Northern Mockingbird. This comes from the gentleman who originally heard it while doing a BBS last week. Mockingbirds have been seen in this refuge on a number of occasions by staff (and others) - whereas Carolina Wren is a statistical anomaly there. So we need a good visual ID! The bird was singing in the (right side of road) pond with dead snags a few hundred yards or so before one completes the loop and begins heading out again. Good birding to all! Al Schirmacher Princeton, MN Mille Lacs & Sherburne Counties