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1 May 2012 Influence of Patch Size and Shape on Occupancy by Shrubland Birds
Corey S. Shake, Christopher E. Moorman, Jason D. Riddle, Michael R. Burchell II
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Populations of many shrubland bird species are declining in the eastern United States. Efforts to restore shrubland and early-successional forest may help to ameliorate these declines. However, uncertainty remains about how the size and shape of habitat patches and the surrounding habitat matrix affect patch occupancy by shrubland passerines. Our objectives were to determine if shrubland birds avoid small or irregularly shaped habitat patches and to identify minimum area requirements for area-sensitive species. Additionally, we sought to determine if the proportion of mature forest cover in the landscape influences patch occupancy. We surveyed 35 individual habitat patches in 2007 and 43 in 2008 for the presence of eight shrubland birds. Then, we modeled the probability of five of these species occupying an individual patch relative to patch area, patch shape, and percent forest cover within 1 km of the patch. We documented evidence of area sensitivity for the Yellow-breasted Chat (Icteria virens) and Prairie Warbler (Setophaga discolor) and estimated their minimum area requirements at 2.3 and 1.1 ha, respectively. The Blue Grosbeak (Passerina caerulea) also was area-sensitive in irregularly shaped patches. Predicted patch-occupancy probability was >0.9 in patches ≥5.5 ha for all area-sensitive species. Patch shape alone and proportion of forest cover were not important predictors of occupancy for these shrubland birds. Restored shrubland and early-successional forest in agricultural landscapes can provide habitat for many shrubland birds, but patches should be >5 ha to maximize shrubland bird diversity.

© 2012 by The Cooper Ornithological Society. 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,
Corey S. Shake, Christopher E. Moorman, Jason D. Riddle, and Michael R. Burchell II "Influence of Patch Size and Shape on Occupancy by Shrubland Birds," The Condor 114(2), 268-278, (1 May 2012).
Received: 12 July 2011; Accepted: 1 November 2011; Published: 1 May 2012
occupancy modeling
Prairie Warbler
shrubland birds
yellow-breasted chat
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