Any explanation come to mind for the male Yellow-rumped Warbler I saw this morning furiously chasing a Common Grackle?

Last year I noted several migrant warblers -- all males -- joined in to chase a Grackle away from a Downy nesthole.
(The tree that held the nesthole, and that each spring hosted a great variety of warblers, is, alas, no more.  It was removed by the Park Service when they were cleaning up in the aftermath of Isabel.  The tree didn't appear to me to be damaged or ailing.  A neighbor said he had asked the workers how they designated the trees to be removed, and was brushed off with "we know what we're doing!"  It occurs to me that tree was in the way of driving their truck in to haul away the other debris.  I know I'll miss it this spring - and sorry for the digression, I guess I'm mourning.)
But today it was just a lone Myrtle chasing the Grackle.  I'm not aware of Myrtles breeding in the immediate vicinity (Georgetown), so what's up?

--
Carrol Cowan
Washington DC
arielamcATatt.net

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