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1 October 2009 Factors Associated with Arrival Densities of Grasshopper Sparrow (Ammodramus savannarum) and Baird's Sparrow (A. Bairdii) in the Upper Great Plains
Marissa A. Ahlering, Douglas H. Johnson, John Faaborg
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Although critical to habitat and population management, the proximate cues that birds use to establish territories are largely unknown. Understanding these cues is important for birds, such as many grassland birds, that exhibit high annual variability in population density and make new habitat-selection decisions annually. Identifying the actual cues used is difficult in the field, but the factors associated with the arrival densities of birds can help uncover variables that are involved in or correlated with cues used for selection. During the summers of 2002–2004, we investigated how weather and local vegetation factors were related to arrival densities of Grasshopper Sparrows (Ammodramus savannarum) and Baird's Sparrows (A. bairdii) at three locations across North Dakota and Saskatchewan. Spring densities of Grasshopper Sparrows were positively correlated with concurrent May precipitation, whereas densities of Baird's Sparrows were negatively correlated with the previous winter's snowfall. We used a model-selection approach to evaluate the vegetation characteristics associated with arrival densities of birds. Grasshopper Sparrow densities showed a strong negative relationship to woody cover, and Baird's Sparrow densities showed a negative relationship to vegetation height and vegetation density near the ground. Our results provide a first detailed look at habitat and weather associations immediately after arrival in spring and an important first step in uncovering factors that may be involved in habitat selection in two grassland species.

© 2009 by The American Ornithologists' Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website,
Marissa A. Ahlering, Douglas H. Johnson, and John Faaborg "Factors Associated with Arrival Densities of Grasshopper Sparrow (Ammodramus savannarum) and Baird's Sparrow (A. Bairdii) in the Upper Great Plains," The Auk 126(4), 799-808, (1 October 2009).
Received: 13 August 2008; Accepted: 20 April 2009; Published: 1 October 2009

A. savannarum
Ammodramus bairdii
Baird's Sparrow
Grasshopper Sparrow
habitat selection
North Dakota
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