I found a decapitated House Sparrow near my feeders on Friday.  I do not
believe it was a cat, as I havn't seen a cat in the 11 months I've lived in
this appartment.  The likely culprit is a Grackle.  I've read about
Grackles doing this, for no apparent reason grabbing the occasional House
Sparrow and either drowning it in the bird bath or decapitating it and
flying off with the head.  I've seen the Grackles in my yard regularly
lunge toward a House Sparrow, but the smaller bird always gets away.

I've been doing some reading on Grackles, and some speculate that they are
moving in the direction of birds-of-prey...evolutionarily speaking.  That
hypothesis attempts to explain their bizarre killing behaviour.

How very interesting...

--davy russell
Burlington, Vermont