A Rusty Blackbird was at Tom Klak's feeder this past week.  The questions
was broached what would the differences have been if it were a Brewers
Blackbird.  I have included a cropped version of Tom's Rusty photo and a
poor, but telling Brewer's image I snagged from the web.  A quick check of
the tertials and wing coverts will quickly separate the two
species--Rusty's with brown edging found on some or most of these feathers
and a bit more difficult character, particularly without comparative
material, is the rather shorter thicker bill of the Brewers.