As the spring advances, more and more of the birds of summer make their appearance.  Most of these we'll only see once, as they pass through Somerville on their way to somewhere more propitious to nest.  Last week it was a battalion of hermit thrushes.  Most of those are gone now, except a few stragglers.  In their wake came the woodpeckers -- a yellow-bellied sapsucker making a quick transit high in the neighbor's trees, and the much more familiar downy woodpecker, a summer regular here.  We've also had a few of our native sparrows -- a song sparrow, I think, and maybe a fox sparrow.  Then this morning, a kinglet passed through, gleaning bugs among the branches.  Here is its portrait.