Grassland Bird Responses to Three Edge Types in a Fragmented Mixed-Grass Prairie

• Published in: Avian conservation and ecology 2012-12, Vol.7 (2), p.6-6, Article art6
• Main Authors: Sliwinski, Maggi S., Koper, Nicola
• Format: Article
• Language: English
• Subjects: Anthus spragueii; Calcarius ornatus; Chestnut-collared Longspur; edge effects; fragmentation; mixed-grass prairie; nonlinear regression; road ecology; Sprague's Pipit
• ISSN: 1712-6568; 1712-6568
• DOI: 10.5751/ACE-00534-070206

One possible factor that may have contributed to the decline of grassland bird populations is edge avoidance. In the mixed-grass prairie, habitat fragmentation is often caused by juxtaposition of habitats with vegetation that is structurally similar to prairie, making it difficult to understand why birds avoid habitat edges. We hypothesized that display height or resource-use strategy, i.e., the degree to which a species depends on grassland habitat, might explain variation in sensitivity to habitat edges among different species of grassland birds. To test our hypotheses, we used data on the abundance of grassland birds in native mixed-grass prairie fields in southern Alberta, Canada, from 2000 to 2002. Point counts were conducted up to 4.1 km from croplands, 2.2 km from roads, and 1.8 km from wetlands. We used nonlinear regression models to determine the distance at which relative abundance of 12 bird species changed in response to edge, and linear regression to determine if display height or resource-use strategy explained variation in response to different types of edges. Variation in response to edge was not explained by display height or resource-use strategy. However, six species avoided wetland edges, two avoided roads, and four avoided cropland. Two species of conservation concern, Chestnut-collared Longspurs (Calcarius ornatus) and Sprague's Pipits (Anthus spragueii), declined in abundance by 25% or more within 1.95 km and 0.91 km, respectively, of cropland edges. Because Chestnut-collared Longspurs avoided croplands to at least 1.95 km, it will be important to prevent further fragmentation of mixed-grass prairies by agriculture.Original Abstract: L'evitement des bordures est un des facteurs avances dans le declin des populations d'oiseaux de prairie. Dans la prairie mixte, la fragmentation d'habitat se presente souvent sous la forme d'une juxtaposition de milieux dont la vegetation est structurellement similaire a la prairie, ce qui rend difficile de comprendre pourquoi les oiseaux evitent les bordures d'habitat. Nous avons emis l'hypothese voulant que la hauteur de parade ou la strategic d'utilisation des ressources, c'est-a-dire a quel degre une espece depend de l'habitat de prairie, expliquerait peut-etre la variation de sensibilite aux bordures chez differentes especes d'oiseaux de prairie. Afin de tester notre hypothese, nous avons utilise des donnees d'abondance des oiseaux de prairie dans des champs de prairie mixte naturelle du sud de l'A