I now have my eyes open for the red-winged blackbirds when I pass that marsh.  They return there every year and I keep my eyes open for them especially for the telltale red wings which could only be seen when they fly.  I did pass a blackbird in that area.  It was sitting in a tree and I did not get a good look at it.  It would have color on its shoulder, which is harder to spot.  I was not able to make a positive ID.