Thanks for the edification. The location of the dark patch and the ruffled
feathers suggested something to do with nesting but the two Phoebe were
in plain view for quite a while and did not return to a nest as far as I could
tell. Then again, there was a small bridge and they do sometimes nest under
the protection of such a structure and therefore may have visited a nest
beyond my scrutiny. Thank heavens it's not a tattoo.