Chapter nine: Understanding Declines in Rusty Blackbirds

Authors

Russell Greenberg, Canada Canadian Wildlife ServiceFollow
Dean W. Demarest, U.S. Fish and Wildlife ServiceFollow
Steven M. Matsuoka, U.S. Fish and Wildlife ServiceFollow
Claudia Mettke-Hofmann, Liverpool John Moores UniversityFollow
David Evers, BioDiversity Research InstituteFollow
Paul B. Hamel, USDA Forest ServiceFollow
Jason Luscier, University of ArkansasFollow
Luke L. Powell, University of MaineFollow
David Shaw, Alaska Bird ObservatoryFollow
Michael L. Avery, USDA/APHIS/WS National Wildlife Research CenterFollow
Keith A. Hobson, Environment CanadaFollow
Peter J. Blancher, Ducks Unlimited CanadaFollow
Daniel K. Niven, National Audubon SocietyFollow

Date of this Version

2011

Citation

Greenberg, R., D. W. Demarest, S. M. Matsuoka, C. Mettke-Hofmann, D. Evers, P. B. Hamel, J. Luscier, L. L. Powell, D. Shaw, M. L. Avery, K. A. Hobson, P. J. Blancher, and D. K. Niven. 2011. Understanding declines in Rusty Blackbirds. Pp. 107– 126 in J. V. Wells (editor). Boreal birds of North America: a hemispheric view of their conservation links and significance. Studies in Avian Biology (no. 41), University of California Press, Berkeley, CA.

Abstract

The Rusty Blackbird (Euphagus carolinus), a formerly common breeding species of boreal wetlands, has exhibited the most marked decline of any North American landbird. North American Breeding Bird Survey (BBS) trends in abundance are estimated to be ‒12.5%/yr. over the last 40 years, which is tantamount to a >95% cumulative decline. Trends in abundance calculated from Christmas Bird Counts (CBC) for a similar period indicate a range-wide decline of ‒5.6%/yr. Qualitative analyses of ornithological accounts suggest the species has been declining for over a century. Several studies document range retraction in the southern boreal forest, whereas limited data suggest that abundance may be more stable in more northerly areas. The major hypotheses for the decline include degradation of boreal habitats from logging and agricultural development, mercury contamination, and wetland desiccation resulting from global warming. Other likely reasons for decline include loss or degradation of wooded wetlands of the southeastern U.S and mortality associated with abatement efforts targeting nuisance blackbirds. In addition, the patchy breeding distribution of this species may inhibit population consolidation, causing local populations to crash when reduced to low levels. Progress in understanding the causes and mechanisms for observed declines has remained limited until recently. Here we present initial attempts to understand the habitat requirements of Rusty Blackbirds and offer specific predictions associated with each of the hypotheses for decline as a way of guiding future research.