Trilling Calls

As I mentioned in a previous post, I am still learning the ins and outs of birding by ear. I have most of the basics down, and I am building a good aural library of the easier calls. But some calls still leave me stymied. One of the hardest groups for me to nail down is the group of trill songs. There are differences, to be sure, but these differences sound much less certain out in the field than they do on the CD. So when I hear one of these trill calls coming from a tree, I am left scratching my head and trying to figure out whether the call is "dry" or "musical." And of course, the bird making the call is nowhere to be found, despite much searching with binoculars. On a hot summer day in D.C., two trilling species can safely be eliminated - dark-eyed junco and swamp sparrow. Chipping sparrow tends to be the most common breeding species of the remaining possibilities, but pine warbler and worm-eating warbler cannot be dismissed out of hand, as they have bred here in the past. (In fact, there is a probable breeding worm-eating warbler in SE DC this summer.) In most of these situations, I try to find the bird for a while, and then move on, frustrated. This happened to me several times today. I could only confirm the chipping sparrow as the source of a song in the Asian Garden; I did not discover the sources of the calls I heard elsewhere in the arboretum.