Poking around the National Audubon Society's Christmas Bird Count website (http://birds.audubon.org/christmas-bird-count) one can graph trends in counts for red-wing blackbirds or other species of interest. Realizing the limitations of such observational data, there appear to have been large swings looking back 20 years but generally greater biomass back in the 1980's up until 1991 (expressed as sightings per search team).
Cordially yours, Geoff Patton, Ph.D. 2208 Parker Ave., Wheaton, MD 20902 301.221.9536
