Vesper Sparrows and Western Meadowlarks Show a Mixed Response to Cattle Grazing in the Intermountain Region of British Columbia

Abstract

Green. 2010. Vesper sparrows and western meadowlarks show a mixed response to cattle grazing in the intermountain region of British Columbia. Avian Conservation and Ecology -Écologie et conservation des oiseaux 5(1): ABSTRACT. Livestock grazing in the shortgrass steppe of the Intermountain region of British Columbia is predicted to have significant effects on grassland habitats and their associated ground-nesting bird communities. We tested whether grazed and ungrazed sites could be discriminated on the basis of their vegetation communities, whether the abundance of two ground-nesting bird species, Vesper Sparrow (Pooecetes gramineus) and Western Meadowlark (Sturnella neglecta), differed between grazed and ungrazed sites, and whether vegetation variables found to differ between grazed and ungrazed plots could be used to predict the abundance of the two bird species at a fine scale. Grazed sites were easily distinguishable from a site that had been ungrazed for >30 years based on the structure and composition of their vegetation communities. However, more detailed grazing categories could not be distinguished on the basis of vegetation characteristics. Despite the existence of grazing effects on vegetation structure and composition, we found no consistent differences in abundance of Vesper Sparrows and Western Meadowlarks between the grazed and ungrazed sites. However, there was weak evidence that the abundance of both species was higher at fine-scale plots (100 m radius point count station) with less bare ground and taller vegetation. Bare ground cover was lower on grazed plots, but vegetation was taller on ungrazed plots. Combined, our results suggest that low intensity grazing leads to grassland habitat change with both negative and positive effects on Vesper Sparrows and Western Meadowlarks, resulting in no net change in their broad-scale abundance.RÉSUMÉ. On pense que le broutement du bétail dans la steppe de la région intramontagnarde de la Colombie-Britannique a des effets significatifs sur les milieux de prairie et les communautés d'oiseaux nichant au sol qui y sont associées. Nous avons testé les hypothèses suivantes : 1) Est-il possible de discriminer les sites broutés des sites non broutés à partir de leur communauté végétale? 2) L'abondance de deux espèces d'oiseaux nichant au sol, le Bruant vespéral (Pooecetes gramineus) et la Sturnelle de l'Ouest (Sturnella neglecta), diffère-t-elle selon le type de sites (broutés vs non broutés)? 3) Les variables relatives à la végétation qui diffèrent entre les sites broutés et les sites non broutés peuvent-elles servir à prévoir l'abondance des deux espèces d'oiseaux à une échelle fine? Les sites broutés ont été faciles à distinguer des sites qui n'avaient pas été broutés depuis plus de 30 ans, d'après la structure et la composition de leur communauté végétale. Toutefois, des catégories de broutement plus détaillées n'ont pas pu être déterminées à partir des caractéristiques végétales. Bien que le broutement ait des effets sur la structure et la composition végé...

Grazing and Songbird Nest Survival in Southwestern Saskatchewan

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“…Effects of livestock grazing can vary regionally to the extent that some species select, avoid, or are neutral to grazing, depending on local conditions (Bock et al 1993). The pastures and haylands of New York State (Norment et al 2010) and the intermountain semidesert region of British Columbia (Harrison et al 2010) differ from the Great Plains, where much of what is known about effects of livestock grazing on birds in North America originates. Nevertheless, Harrison et al (2010) and Norment et al (2010) concluded that livestock management is compatible with the conservation of a number of grassland bird species, consistent with many studies from the Northern Great Plains (e.g., Bareiss et al 1986, Kruse and Bowen 1996, Koper and Schmiegelow 2007.…”

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“…Because not all agricultural practices are inevitably harmful (e.g., Harrison et al 2010, Norment et al 2010, knowing which practices are and might require intervention, can help to conserve the intellectual energy of the scientific conservation community to address other worthy and complex issues, such as those presented by migration mortality (Dinsmore et al 2010) or intra-annual variability in land management (Shustack et al 2010). Where a lack of information about natural history is needed to enable conservation, scientists need to work systematically to fill those knowledge gaps (Villard and Nudds 2009).…”