I took advantage of our school's Earth Day service projects to spend some time hiking through the county park across the road from my school and was pleasantly surprised at the birds that were around. Eastern Bluebirds flitted along the edge of the tree line and Song Sparrows sang continuously but it was the song I didn't recognize that really caught my attention. I skulked around a stand of pines that mark the spot where an old house used to be and I could see a couple of dark birds jumping from branch to branch. They finally gave me a good look and here were two Eastern Towhees moving and calling through the pines.
Now I had never heard the call they were making and had I not noticed it as a call I didn't know I would have never gotten as good a look as I did. If they had been making their regular "Drink your tea" song I could have identified it at a distance and kept going but I wanted to identify that thing that was unfamiliar.
This may sound obvious but it's like I tell my students, study what you don't know, not what you do know.