Rusty Blackbirds, considered common to abundant one-hundred years ago, have declined precipitously during the last four decades. Estimates of decline vary between 85 percent, based on Christmas Bird Counts, and 97 percent, based on Breeding Bird Survey results along the southern margin of the Rusty’s breeding range. The losses are staggering. Uncertainty is high, Rusty Blackbirds are difficult to find and count during winter. Christmas Bird Counts find small numbers. Breeding Bird Surveys barely penetrate their northern breeding range. But everyone agrees that the formerly abundant Rusty Blackbird is now uncommon to rare almost everywhere it is found, and the species is in trouble.
The causes must be determined soon, and actions to protect vital habitats and resources are necessary now. The International Rusty Blackbird Technical Working Group assembled during 2005 to study the problem, and more than twenty scientists coordinate new research investigating possible causes for the decline. The group is led by Russell Greenberg, head of the Smithsonian Migratory Bird Center. Beginning in 2009, the working group has involved citizen scientists, too. Birders from many states entered their observations into eBird during the effort. Ohio was the lead reporting state during 2009. Ohio birders canvassed our state and discovered important hotspots close to home, including Calamus Swamp. The 2011 Rusty Blackbird Hotspot Blitz from January 30 through February 15 will gather data about the winter distribution of our declining swamp blackbird.
Rusty Blackbirds eat more invertebrate proteins and lipids than other blackbirds. They eat nuts, too: thin walled nuts and water soaked acorns are favorites. Shallow water is the key; Rusties don’t mind wading, but they like to keep their bellies dry. If the water is too deep, Rusty Blackbirds lose access to important food sources. One possible cause for the precipitous decline of Rusty Blackbirds may be modern flood management in vast bottomland green tree swamps along southern rivers in the core of their winter range. Natural water level fluctuations ensure there will be areas of shallow pooled water along riparian corridors. Modern hydrological engineering and wildlife management practices keep bottomlands under deeper water better suited for water storage and dabbling ducks.
Rusty Blackbirds are studied in their breeding range to gain better understanding of their breeding distribution and trends. Alas, it appears they may be threatened there, too. Great swaths of boreal forest are clear cut to feed the voracious world market for spruce and fir pulp used in making toilet tissue and sundries. Rebounding clear cuts are very attractive to breeding Rusty Blackbirds. The brushy regrowth mimics bog and streamside edge habitat normally selected by Rusty Blackbirds. Clear cuts attract very high densities of nesting blackbirds. Researchers initially suggested that the recent huge growth of winter logging deep in the frozen boreal forest might help slow the decline of Rusty Blackbirds. When they studied these high density nesting areas, they discovered very low survivorship. Very few young Rusties fledged and dispersed from the clear cuts.
Further study discovered a furry culprit, red squirrels. Hyper-predation by red squirrels attracted to the high nest densities in rebounding clear cuts made these breeding sites ecological sinks for the Rusty Blackbird. More study is needed, north and south, summer and winter. The mysterious decline of the Rusty Blackbird is a multi- faceted problem.