Master of Science (MS)


Renewable Natural Resources

Document Type



With an estimated population loss of at least 5% annually and a 100-year history of decline, Rusty Blackbirds (Euphagus carolinus) are one of the fastest declining bird species in North America. Determining cause of decline is important, both for conserving the species and for identifying threats to the wooded wetland ecosystems they use on their boreal breeding-grounds and their wintering-grounds in the southeastern United States. One hypothesis is that loss of wintering ground habitat, possibly in conjunction with competition or disease, is causing Rusty Blackbird decline. To determine contribution of wintering ground conditions, it is important to understand the behaviors and habitat requirements that make these birds prone to decline. My research objectives were to develop survey strategies for detecting and quantifying Rusty Blackbird presence, to examine inter- and intraspecific associations for potential competition, and to determine habitat requirements at spatial scales appropriate to foraging movements. The present study uses data from 550 survey occasions and 163 independently collected birder observations to examine survey methods and seasonal trends over two winters. Occupancy modeling was used to investigate flocking behavior and habitat associations (at 25 m and 100 m scales) at 74 unique sites (naïve occupancy = 0.82, average occupancy by survey round = 0.51). Results indicate that Rusty Blackbirds may be less dependent on forested habitat than previously thought, but show strong a strong relationship to availability of wet ground. Range-wide alterations in hydrological processes, due to drainage or flood control, could lead to decreased quality or availability of shallow-water habitat and aquatic food resources. Rusty Blackbirds frequently flock with other blackbird species, and show similarities in use of open habitats. Competition cannot be ruled out and could worsen with use of degraded habitat. Overall results suggest that wintering behavior and habitat changes are likely contributors to long-term and continuing Rusty Blackbird decline.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Stouffer, Philip C