Thanks to everyone who offered suggestions for my: see-saw-to-Eat! bird. No one seemed completely certain but brown creeper was the winner in total mentions, along with all three chickadees, white-crowned sparrow, Bewick's wren, and a few others. Perhaps this time of year it's a male tuning up for his full song? If I figure it out for sure I'll let everyone know. Thanks again!

Kerri W. Scarbrough
Woodinville, WA