This is a blue-gray gnatcatcher.   And here’s a recording of his call notes:   There’s a robin singing in the background; the gnatcatcher’s vocalizations are the worried-sounding scolds.   So he’s not the fanciest or most attention-getting bird around.  He weighs around 6 grams, hangs out in treetops, moving constantly, and can’t sing worth a damn (from a biased, robin-centric standpoint), but he’s actually a fairly common bird.  Once you tune in to his vocalizations, you start to notice gnatcatchers all around, especially in wet woods.  Since this spring’s migration started in earnest a couple of weeks ago, I scarcely remember a walk we’ve taken when I haven’t heard at least one gnatcatcher.   The problem is that, until recently, I had no…