Habitat Occupancy by Rusty Blackbirds Wintering in the Lower Mississippi Alluvial Valley

• Published in: The Condor (Los Angeles, Calif.) Calif.), 2010-11, Vol.112 (4), p.841-848
• Main Authors: Luscier, Jason D, Lehnen, Sarah E, Smith, Kimberly G
• Format: Article
• Language: English
• Subjects: Agricultural land; Agriculture; Aquatic habitats; Birds; Bottomland; Bottomland forests; bottomland hardwood forests; Canopies; Euphagus carolinus; Flocks; Floods; Food; Forest habitats; Forested wetlands; Forests; Habitat; Habitat conservation; Habitat selection; Habitat utilization; Habitats; Hardwood forests; lower Mississippi Alluvial Valley; occupancy; Ornithology; RESEARCH PAPERS; Rusty Blackbird; Studies; Swamps; Trees; Water levels; Wetlands; winter habitat use
• ISSN: 0010-5422; 1938-5129; 2732-4621
• DOI: 10.1525/cond.2010.100147

The Rusty Blackbird (Euphagus carolinus) has declined by 90% since the 1960s, possibly from conversions of forested wetlands in the southeastern U.S. to agriculture. Because its habitat use during the nonbreeding season had not been quantified, we estimated occupancy rates of Rusty Blackbirds wintering in the lower Mississippi Alluvial Valley in relation to habitat type (four types of bottomland forest and adjacent agricultural fields), tree density, canopy cover, and water cover. In January and February, we surveyed 89 sites eight times during 2006, 117 and 109 sites 10 times during 2007 and 2008, respectively. Occupancy of individual birds, estimated from their presence or absence at a site, was generally high and greater in 2006 (0.71) than during either 2007 (0.43) or 2008 (0.37). Occupancy of flocks, estimated from presence or absence of ≥20 individuals, was highest in 2006 (0.46), lowest in 2007 (0.17), and intermediate in 2008 (0.30), possibly because of water levels fluctuating from year to year. Rusty Blackbirds were not as specialized in habitat use as expected; habitat characteristics did not consistently predict occupancy of either individuals or flocks. Occupancy of individuals increased with canopy cover during 2007, and occupancy of flocks decreased with tree density during 2006. In 2008, occupancy of individuals increased with tree density and was higher in wet bottomland forest (0.51) than in other habitats (0.31–0.35). Further research is needed to determine whether this lack of habitat specificity is widespread and possibly the result of diverse food requirements during the nonbreeding season.