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1 January 2013 Evaluating the Roles of Visual Openness and Edge Effects on Nest-Site Selection and Reproductive Success in Grassland Birds
Alexander C. Keyel, Allan M. Strong, Noah G. Perlut, J. Michael Reed
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Abstract

In some species, habitat edges (ecotones) affect nest-site selection and nesting success. Openness, or how visually open a habitat is, has recently been shown to influence grassland bird density and may affect nest-site selection, possibly by reducing the risk of predation on adults, nests, or both. Because edge and openness are correlated, it is possible that effects of openness have been overlooked or inappropriately ascribed to edge effects. We tested the roles of edges and visual openness in nest-site selection and nesting success of two grassland passerines, the Bobolink (Dolichonyx oryzivorus) and Savannah Sparrow (Passerculus sandwichensis), in the Champlain Valley, Vermont. We also evaluated the sensitivity of our results to alternative definitions of edge on our landscape. Bobolink (n = 580) and Savannah Sparrow nests (n = 922) were located on seven hay fields and three pastures from 2002 to 2010. Both species avoided placing nests near edges and in less open habitat compared with expectations based on random placement. When the effects of openness and edge were separated, less open habitats were still avoided, but edge responses were less clear. These results were robust to different definitions of habitat edge. We found no strong relationships between either openness or edges and reproductive success (numbers of eggs and fledglings, percentage of eggs producing fledglings, and nest success), although there may be an edgespecific openness effect on timing of reproduction (clutch completion date). Our results support openness as an important factor in nest-site selection by grassland birds.

© 2013 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, http://www.ucpressjournals.com/reprintInfo.asp.
Alexander C. Keyel, Allan M. Strong, Noah G. Perlut, and J. Michael Reed "Evaluating the Roles of Visual Openness and Edge Effects on Nest-Site Selection and Reproductive Success in Grassland Birds," The Auk 130(1), 161-170, (1 January 2013). https://doi.org/10.1525/auk.2012.12039
Received: 9 March 2012; Accepted: 9 November 2012; Published: 1 January 2013
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KEYWORDS
antipredator
Bobolink
Dolichonyx oryzivorus
fragmentation
habitat selection
openness
Passerculus sandwichensis
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