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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...

Tree cavities provide a critical resource for cavity-nesting animals, and high quality cavities can be difficult for animals to acquire in habitats where competition is high. We investigated the breeding performance of Lewis’s Woodpeckers in three habitat types in British Columbia, Canada in 2013 and 2014. We also assessed whether the number of nest competitors and cavity availability influenced the habitat specific breeding performance of this threatened cavity nesting species. We found that daily nest survival rate was lower in burned habitat (0.15 ± 0.08 (0.05–0.37)) than in live pine (0.72 ± 0.10 (0.51–0.87)) or cottonwood (0.69 ± 0.09 (0.51–0.83)) habitats. However, hatching success (the proportion of eggs that hatch) was lower in live pine habitat (0.59 ± 0.09 95% CI) than burned (0.77 ± 0.19 95% CI) or cottonwood (0.80 ± 0.07 95% CI) habitat, and the fledging success of successful nests in live pine and burned habitat (1.86 ± 0.31 and 1.88 ± 0.59 95% CI, respectively) was slightly lower than in cottonwood habitat (2.61 ± 0.45 95% CI). Consequently, Lewis’s Woodpeckers in cottonwood habitat produced more fledglings per nesting attempt (2.05 ± 0.49 95% CI) than in live pine (1.53 ± 0.35 95% CI) or burned (0.79 ± 0.49 95% CI) habitat. Habitats differed in the number of nesting competitors and the number of suitable cavities surrounding active Lewis’s Woodpecker nests. Our results showed that cavity density best explained breeding performance differences although the mechanisms remain unclear. There was no evidence that the number of heterospecific nest competitors, including the invasive European Starling (Sturnus vulgaris), explained or influenced Lewis’s Woodpecker breeding performance. Cavity density influenced the productivity of successful nests but did not explain habitat differences in hatching success or daily nest survival. Further work is required to understand the mechanistic basis for the habitat specific breeding performance of Lewis’s Woodpeckers. Habitat differences in breeding performance in British Columbia are not consistent with those in other regions, highlighting the importance of regionally-specific demographic data for managing species at risk.

Territorial clustering within larger, continuous patches of seemingly appropriate habitat could indicate that a species has additional, finer scale habitat requirements. Studying fine-scale (e.g., territory-level) habitat selection using methods that elucidate individual preferences may allow us to identify resources that influence species distributions. We examined breeding territory selection in the sagebrush Brewer's Sparrow (Spizella breweri Cassin, 1856) at the northern extent of its range to test for influences on fine-scale habitat selection. We used an information-theoretic approach to evaluate models relating a suite of vegetation characteristics to breeding habitat selection. We employed two methods: (1) assessment of patch occupancy at a territory scale and (2) examination of individual decisions relating to settlement and dispersal. We found that patch occupancy was most consistently predicted by models that included the cover of big sagebrush (Artemisia tridentata Nutt.) with the greatest likelihood of occupancy at 20%-25% cover. However, assessment of settlement and dispersal decisions did not identify additional fine-scale preferences for other vegetation characteristics. Vegetation cover also did not influence breeding success, indicating that within the vegetation range found in Brewer's Sparrow territory clusters, there is little benefit in basing individual settlement or dispersal decisions on vegetation cover. Résumé : Le regroupement d'un territoire avec des taches d'habitat en apparence appropriées, mais plus grandes et continues, pourrait indiquer qu'une espèce possède des besoins additionnels d'habitat à une échelle plus fine. L'étude de la sélection d'habitat à échelle fine (par ex., au niveau du territoire) en utilisant des méthodes qui mettent en lumière les préférences individuelles permet peut-être d'identifier les ressources qui influencent la répartition des espèces. Nous examinons la sélection du territoire de reproduction chez le bruant de Brewer des armoises (Spizella breweri Cassin, 1856) à la limite boréale de son aire de répartition afin de vérifier les influences sur la sélection d'habitat à échelle fine. Nous utilisons une approche basée sur la théorie de l'information afin d'évaluer des modèles qui relient une série de caractéristiques de la végétation à la sélection de l'habitat de reproduction. Nous employons deux méthodes, (1) une évaluation de l'occupation des taches à l'échelle du territoire et (2) un examen des décisions individuelles concernant l'établissement et la dispersion. Ce sont les modèles qui incluent la couverture de la grande armoise (Artemisia tridentata Nutt.) qui prédisent l'occupation des taches de la façon la plus constante; la plus grande probabilité d'occupation se situe à une couverture de 20 % -25 %. L'évaluation des décisions d'établissement et de dispersion n'a pas, cependant, identifié de préférences additionnelles à échelle fine pour d'autres caractéristiques de la végétation. De plus, la couverture végétale n'influence pas le succès de la rep...

Livestock grazing in the shortgrass steppe of the Intermountain region of British Columbia may have a negative impact on ground‐nesting birds, but evidence of such an impact is lacking. We examined nest‐site selection and productivity of ground‐nesting Vesper Sparrows (Pooecetes gramineus) across sites with different grazing histories. From 2006 to 2008, we monitored Vesper Sparrow nests and measured vegetation characteristics known to be affected by grazing within nest patches. We used an information‐theoretic approach to test the relative importance of grazing‐affected vegetation variables as predictors of nest‐site selection, nest survival, and nestling condition. Vesper Sparrows selected nest sites with greater cover of late‐seral grass species that decrease in occurrence in response to grazing (i.e., “decreasers”) than was available in random patches in the same territories. Daily nest survival was also lower for nests surrounded by shorter vegetation (odds ratio = 1.12). However, “decreaser” cover was not associated with either of the two indices of productivity measured (daily nest survival probability and nestling condition). In addition, vegetation height, although an important driver of success, was not linked with nest‐site selection, and no vegetation‐cover variable was positively associated with productivity, despite nest concealment being central to our predictions. This suggests that predation risk for nests in areas with shorter vegetation was being elevated through some factor unrelated to concealment. Our results show that grazing reduced both the availability of suitable habitat for and nesting success of Vesper Sparrows, indicating that grazing could pose a threat to population persistence at a broader scale and could potentially contribute to observed declines. Additional research is needed to determine if grazing guidelines in the Intermountain region of British Columbia should be amended, better enforced, or both to prevent regional declines in populations of ground‐nesting grassland birds.