Managing Mixed-Grass Prairies for Songbirds Using Variable Cattle Stocking Rates

Most remaining grasslands are used for livestock grazing; stocking rates could be managed to help stop declining songbird populations. We examined the effects of stocking rates on grassland songbirds in northern mixed-grass prairies using a beyond-Before-After-Control-Impact manipulative experiment in Canada's Grasslands National Park and adjacent community pastures. The study area consisted of nine 300-ha pastures grazed at a range of stocking rates starting in 2008. We conducted songbird surveys at six upland plots in each pasture from 2006-2010 and measured vegetation structure within each plot from 2008-2010 (n = 54). We evaluated the effects of stocking rates on habitat structure and songbird abundance using linear and generalized linear mixed models. Baird's sparrow (Ammodramus bairdii) relative abundance declined with increasing stocking rates. Chestnut-collared longspur (Calcarius ornatus) relative abundance increased only at higher stocking rates, indicating a possible threshold effect. Savannah sparrow (Passerculus sandwichensis) relative abundance decreased with stocking rates above 0.4 AUM after a year of grazing. Sprague's pipit (Anthus spragueii) relative abundance declined with grazing, but the effect was weak and only significant in 1 year. Western meadowlark (Sturnella neglecta) abundance was unaffected by grazing. Stocking rates may be used to benefit grassland songbirds and may alter avian communities after as little as 1 month of livestock grazing. Applying a range of stocking rates regionally may provide habitat for many species. © 2015 Society for Range Management. Published by Elsevier Inc. All rights reserved.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Data from: Differences in spatial synchrony and interspecific concordance inform guild-level population trends for aerial insectivorous birds

Many animal species exhibit spatiotemporal synchrony in population fluctuations, which may provide crucial information about ecological processes driving population change. We examined spatial synchrony and concordance among population trajectories of five aerial insectivorous bird species: chimney swift Chaetura pelagica, purple martin Progne subis, barn swallow Hirundo rustica, tree swallow Tachycineta bicolor, and northern rough-winged swallow Stelgidopteryx serripennis. Aerial insectivores have undergone severe guild-wide declines that were considered more prevalent in northeastern North America. Here, we addressed four general questions including spatial synchrony within species, spatial concordance among species, frequency of declining trends among species, and geographic location of declining trends. We used dynamic factor analysis to identify large-scale common trends underlying stratum-specific annual indices for each species, representing population trajectories shared by spatially synchronous populations, from 46 yr of North American Breeding Bird Survey data. Indices were derived from Bayesian hierarchical models with continuous autoregressive spatial structures. Stratum-level spatial concordance among species was assessed using cross-correlation analysis. Probability of long-term declining trends was compared among species using Bayesian generalized linear models. Chimney swifts exhibited declining trends throughout North America, with less severe declines through the industrialized Mid-Atlantic and Great Lakes regions. Northern rough-winged swallows exhibited declining trends throughout the west. Spatial concordance among species was limited, the proportion of declining trends varied among species, and contrary to previous reports, declining trends were not more prevalent in the northeast. Purple martins, barn swallows, and tree swallows exhibited synchrony across smaller spatial scales. The extensive within-species synchrony and limited concordance suggest that population trajectories of these aerial insectivores are responding to large-scale but complex and species- and region-specific environmental conditions (e.g. climate, land use). A single driver of trends for aerial insectivores as a guild appears unlikely