In my local patch (Bear Creek in Boulder Open Space and Mountain Parks), Blue-gray Gnatcatchers are each year one of the earlier migrants to set up shop. I have, for example, had multiple pairs by April 19. And one of the great things about this bird is how pugnacious they are; you can hardly peep without one of them popping up to glower at you.
This year, to date, I have seen none along nearly a mile of nice shrubby habitat. I hope that others are seeing lots of this bird. ??