Declining songbirds caught in a complex web
Date:October 7, 2015
Source:Central Ornithology Publication Office
The bird that's experienced the steepest population declines in North America in recent decades is also one that few people have heard of: the Rusty Blackbird. Rusty Blackbird (Euphagus carolinus) populations have decreased by about 95% in the last fifty years, but the reasons are not well understood; it doesn't help that their preferred breeding habitat, stunted conifers deep in the wetlands of the boreal forest, makes finding and studying them difficult. New research in The Condor: Ornithological Applications aims to disentangle some of the interacting factors that may be responsible for the decline.
Shannon Buckley Luepold of the SUNY College of Environmental Science and Forestry and her colleagues spent two years collecting data on Rusty Blackbirds nests and their surrounding habitat in Maine and New Hampshire, and uncovered a web of connections between timber harvesting practices, spruce and fir cones, red squirrels, and Rusty Blackbird nesting success.
In the breeding seasons of 2011 and 2012, Buckley Luepold and her co-authors were able to locate 72 Rusty Blackbird nests and install motion-triggered, infrared cameras to watch for predators at 29 of them. Enduring swarms of biting black flies, numerous flat tires, and even a night spent stranded in the woods with a broken ATV, they also collected a variety of data on habitats where the birds nested, including vegetation density, spruce and fir cone production, and red squirrel abundance. After abundant cone production in 2011, squirrel numbers increased significantly in 2012, which is when nest survival was lower and when all of the observed red squirrel predation on eggs and nestlings occurred. A big year for cone production leads to a big year for the squirrels that eat them. This is bad news for Rusty Blackbirds, as their eggs are also on the squirrels' menu.