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Book preview: A multi-scale analysis linking prairie breeding birds to site and landscape factors including USGS GAP data (Volume 2007) by Paul Hendricks

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Author: Paul Hendricks
Title: A multi-scale analysis linking prairie breeding birds to site and landscape factors including USGS GAP data (Volume 2007)
Publisher: Helena, Mont. : Montana Natural Heritage Program
Subject (keywords, tags): Grassland birds; Grassland birds; Bird populations; Plants; Plants


Literature cited: p. 20-23
Grassland and shrub-steppe bird populations have experienced more substantial declines during the last century than any other groups of birds throughout North America. Our study area in Southeast Montana has abundant natural habitat for these birds but invasive plant species, agricultural conversion, and energy development are altering natural conditions in the area and may affect this group of declining birds. We sampled 116 locations in southeast Montana for breeding bird presence during early summer 2007. A primary goal was to better document the distribution and abundance of this bird group in the study area. Another objective was to relate breeding bird presence, with an emphasis on Montana Species of Concern, to site and landscape factors so managers may better focus limited resources. Site vegetation and ground cover characteristics were directly measured at each sampling site. Landscape variables were derived for three landscape scales as measured in 200 m, 800 m, and 5,000 m radius circles around the sampling point. USGS GAP land cover data was aggregated into a few general classes and several other landscape variables (measures of roads, watercourses, human populations, energy leases, wetlands, topographic roughness, etc.) were derived from other GIS data sources. A univariate analysis compared differences in site ground cover and vegetation characteristics to the presence of six grassland and five shrubland bird species, six of which (four grassland and two shrubland species) are Montana Species of Concern (SOC). For the six SOC birds we additionally used logistic regression and non-metric multidimensional scaling ordination to analyze how these birds responded to site and landscape factors at 200, 800, and 5,000 m scales. The importance of site or landscape factors varied with individual species. Site factors may be more important for some species (e.g. Brewer?s Sparrow, Spizella breweri), and landscape factors for others (e.g. Sprague?s Pipit, Anthus spragueii). For other species, there was a more balanced response to site and landscape factors. Site variables, especially grass density, maximum vegetation height, and maximum sagebrush height, appeared to be strongly related to the presence of particular bird species on point counts, although the presence of some species was also related to site landcover variables (% bare ground, % grass cover, % sage canopy). Grassland species tended to occur at sites with shorter and less dense grass. Shrubland species tended to occur at sites with taller sagebrush and more extensive sagebrush cover. However, there were exceptions to these trends for both groups. Univariate patterns may have been affected by three confounding factors. First, the relatively small number of sites sampled may have masked real, but possibly weak, relationships of some bird species with the measured proximate vegetation and landcover variables. Second, point counts were conducted about evenly in two discrete time periods (mid-June and early July) during which vegetation structure (especially grass) continued to change significantly in response to wet and warm conditions; some bird species may have abandoned sites before they could be sampled, because grass density and height (especially of exotic annuals) crossed a tolerance threshold. Third, the study area was so large that some vegetation conditions favorable to particular bird species were encountered only during one of the two sample periods, and this biased the temporal results of the counts and habitat measurements. Nevertheless, significant patterns between each bird species and one or more appropriate habitat variables were identified in the univariate analysis. Despite data caveats of small sample size for some species and a relatively extended sampling season, results suggest that any management of grassland bird species will benefit from both landscape and site considerations. GAP-derived variables, especially at the 5,000 m scale, were important and often proved to be stronger predictors of breeding bird habitat choice than vegetation variables we directly measured at the site. Managers concerned with these declining grassland bird species may wish to apply species-appropriate site vegetation management with knowledge of landscape characteristics and current GAP land cover maps. With additional bird sampling data we will be able to apply our analysis techniques with available GIS data to model priority landscapes for specific birds that will enable focused conservation and habitat management. However, it is already known that maintaining the suite of grassland and shrubland bird species currently present requires maintaining a mosaic of grass and shrub habitat patches of various structures and patch sizes. Grazing and fire are two tools that, when used judiciously and based on the needs of each species, can help achieve this goal, but no net loss of grassland and shrubland habitat should b

Contributor: Montana State Library
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