Grassland Bird Species Research Articles

Ants and plants as indicators of biodiversity, ecosystem services, and conservation value in constructed grasslands

Grasslands are constructed for soil and wildlife conservation in agricultural landscapes across Europe and North America. Constructed grasslands may mitigate habitat loss for grassland-dependent animals and enhance ecosystem services that are important to agriculture. The responses of animal species richness and abundance to grassland habitat quality are often highly variable, however, and monitoring of multiple taxa is often not feasible. We evaluated whether multiple animal taxa responded to variation in constructed grassland habitats of southwest Ohio, USA, in ways that could be predicted from indicators based on quality assessment indices, Simpson diversity, and the species richness of ants and plants. The quality assessment indices included a widely used Floristic Quality Assessment (FQA) index, and a new Ant Quality Assessment (AntQA) index, both based on habitat specificity and species traits. The ant and plant indicators were used as predictor variables in separate general linear models of four target taxa—bees, beetles, butterflies and birds—with response variables of overall species richness and abundance, and subsets of taxa that included the abundance of ecosystem-service providers and grassland-associated species. Plant Simpson diversity was the best-fitting predictor variable in models of overall bee and beetle abundance, and the abundance of bees classified as ecosystem-service (ES) providers. FQA and plant richness were the best predictors of overall butterfly species richness and abundance. Ant species richness was the best predictor of overall bird species richness and abundance as well as the abundance of ES birds, while the AntQA index was the best predictor for the abundance of grassland bird and butterfly species. Thus, plant Simpson diversity and ant species richness were the most effective indicators for complementary components of grassland animal communities, whereas quality assessment indices were less robust as indicators and require more knowledge on the habitat specificity of individual ant and plant species.

Cattle grazing and grassland birds in the northern tallgrass prairie

ABSTRACTWith the loss of over 70% of North America's grasslands (Samson et al. 2004), grassland birds increasingly rely on habitat that is privately owned and managed for livestock production. Therefore, it is critical to understand how livestock grazing influences grassland bird abundance and community structure. We evaluated the response of 4 obligate grassland bird species to grazing intensity, vegetation structure, ecological site description, and burning across a landscape including pastures with no recent grazing to pastures experiencing grazing intensities similar to that for private livestock production operations. We evaluated models using a binomial N‐mixture model implemented in the R package unmarked. Overall, 3 of the 4 obligate species included positive relationships with grazing intensity in the top abundance model (i.e., grasshopper sparrow [Ammodramus savannarum], bobolink [Dolichonyx oryzivorus], and upland sandpiper [Bartramia longicauda]), suggesting the range of grazing intensities evaluated (0–4.57 animal months/ha) did not negatively affect the abundance of these species. Marbled godwit (Limosa fedoa) abundance, however, was higher with greater variability in litter depth but was not directly related to grazing intensity. Finally, the effect of year was correlated with decreasing precipitation over the course of the study and had the greatest influence on community composition with some community separation by grazing intensity. Our results suggest that cattle grazing can positively influence the abundance of some grassland bird species but annual variation in weather patterns can influence community composition at sites regardless of management decisions. © 2016 The Wildlife Society.

Conservation-priority grassland bird response to urban landcover and habitat fragmentation

As urbanization in the landscape increases, some urban centers are setting aside habitat for wildlife. This habitat may be particularly valuable to declining or conservation-priority species. One group in particular need of conservation actions that may benefit from habitat located in urban areas is grassland birds. Declines of grassland bird species have been particularly severe in the Midwestern U.S., where most grassland cover has been lost, fragmented, and surrounded by unsuitable habitat. Conservation efforts have focused on protecting large grasslands surrounded by minimal amounts of trees and development. Although urban development is considered hostile to grassland birds, this assumption has received little attention. In heavily fragmented landscapes where habitat is limited, urban grasslands may be of significant value to grassland birds. We examined grassland bird response to development and additional landscape and habitat variables in the greater Chicago metropolitan area. In 2012 and 2013, we surveyed bird communities in grassland patches along a gradient of urbanization and patch sizes. Density of Savannah Sparrows (Passerculus sandwichensis) increased with amount of development, while density of Sedge Wrens (Cistothorus platensis) decreased. Development did not appreciably impact Bobolinks (Dolichonyx oryzivorus), Dickcissels (Spiza americana), Eastern Meadowlarks (Sturnella magna), Grasshopper Sparrows (Ammodramus savannarum), or Henslow’s Sparrows (Ammodramus henslowii). Patch size had a positive effect on species densities. These results indicate that for many conservation-priority grassland birds, urban landcover surrounding grasslands generally has neutral rather than negative effects on habitat use. Therefore, grasslands in developed landscapes may provide valuable contributions to regional conservation efforts.

Effects of water level and grassland management on alpha and beta diversity of birds in restored wetlands

Summary Nearly 60% of European wetlands have been lost to drainage or to the cessation of grassland management. Large amounts of resources are put into wetland restoration with the aim to recover biodiversity. However, few studies have simultaneously evaluated effects of management, wetness and flooding dynamics on biodiversity of restored wetlands such as seasonally flooded wet grasslands. We inventoried bird communities over 4 years at 137 sites (each 3·1 ha) within five restored wet grassland areas in Sweden to investigate whether species richness and occurrence of 12 common wet grassland species were related to (i) local conditions such as management (grazing, mowing and unmanaged areas), basic wetness and spring flooding dynamics. Further, we investigated whether (ii) the composition of the adjacent landscape (20 ha) related to local bird diversity and (iii) species turnover (i.e. beta diversity) differed between sites characterized by their basic wetness, degree of flooding and predominant management regime. Local species richness was positively linked to degree of flooding and basic wetness of grasslands but not to type of grassland management. Species richness tended also to be negatively linked to proportion of forest at the landscape scale. Although variable, the same results were also true concerning the probability of the occurrence of a single species at the local scale. Species turnover between sites, and thus total species richness, was distinctly higher in (i) grazed as compared to mowed grasslands except in dry non‐flooded grasslands and (ii) flooded as compared to non‐flooded sites. Similar patterns held for the subset of 12 red‐listed species. We suggest that the high beta diversity in grazed and flooded grasslands is driven by the heterogeneous vegetation structure, resulting in good conditions for foraging and nesting for several wet grassland bird species. Synthesis and applications. The selection of wetlands for conserving wet grassland birds should prioritize temporary flooded grasslands of moderate wetness, preferably far from forest edges. Restoration and management of wet grasslands should include water level management, removal of shrubs and trees, and low‐intensity grazing, whereas mowing could be used in non‐flooded grasslands of low basic wetness.

Do ducks and songbirds initiate more nests when the probability of survival is greater?

Nesting chronology in grassland birds can vary by species, locality, and year. The date a nest is initiated can influence the subsequent probability of its survival in some grassland bird species. Because predation is the most significant cause of nest loss in grassland birds, we examined the relation between timing of nesting and nest survival. Periods of high nest survival that correspond with the peak of nesting activity might reflect long-term adaptations to specific predation pressures commonly recurring during certain periods of the nesting cycle. We evaluated this theory by comparing timing of nesting with date-specific nest survival rates for several duck and passerine species breeding in north-central North Dakota during 1998–2003. Nest survival decreased seasonally with date for five of the seven species we studied. We found little evidence to support consistent relations between timing of nesting, the number of nest initiations, and nest survival for any species we studied, suggesting that factors other than nest predation may better explain nesting chronology for these species. The apparent mismatch between date-specific patterns of nest survival and nest initiation underscores uncertainty about the process of avian nest site selection driven mainly by predation. Although timing of nesting differed among species, the general nesting period was fairly predictable across all years of study, suggesting the potential for research activities or management actions to be timed to take advantage of known periods when nests are active (or inactive). However, our results do not support the notion that biologists can take advantage of periods when many nests are active and survival is also high.

Avoidance of unconventional oil wells and roads exacerbates habitat loss for grassland birds in the North American great plains

Oil development in the Bakken shale region has increased rapidly as a result of new technologies and strong demand for fossil fuel. This region also supports a particularly high density and diversity of grassland bird species, which are declining across North America. We examined grassland bird response to unconventional oil extraction sites (i.e. developed with hydraulic fracturing and horizontal drilling techniques) and associated roads in North Dakota. Our goal was to quantify the amount of habitat that was indirectly degraded by oil development, as evidenced by patterns of avoidance by birds. Grassland birds avoided areas within 150m of roads (95% CI: 87–214m), 267m of single-bore well pads (95% CI: 157–378m), and 150m of multi-bore well pads (95% CI: 67–233m). Individual species demonstrated variable tolerance of well pads. Clay-colored sparrows (Spizella pallida) were tolerant of oil-related infrastructure, whereas Sprague's pipit (Anthus spragueii) avoided areas within 350m (95% CI: 215–485m) of single-bore well pads. Given these density patterns around oil wells, the potential footprint of any individual oil well, and oil development across the region, is greatly multiplied for sensitive species. Efforts to reduce new road construction, concentrate wells along developed corridors, combine numerous wells on multi-bore pads rather than build many single-bore wells, and to place well pads near existing roads will serve to minimize loss of suitable habitat for birds. Quantifying environmental degradation caused by oil development is a critical step in understanding how to better mitigate harm to wildlife populations.

Patch-burn grazing management, vegetation heterogeneity, and avian responses in a semi-arid grassland

Anthropogenic changes to disturbance regimes in grasslands, and associated homogenization of vegetation structure, have been implicated as factors contributing to declines in populations of grassland birds in North America. We examined the influence of patch-burn grazing management, which employs spatiotemporal interactions between fire and livestock grazing guided by historical disturbance patterns, on vegetation structure and bird abundance in shortgrass steppe in northeastern Colorado, USA. All study pastures were grazed by cattle at moderate stocking rates from May to October each year. In the patch-burn treatment, we burned 25% of each pasture in autumn (Oct or Nov) each year during 2007–2010; control pastures were not burned. Patch-burn grazing management increased vegetation heterogeneity by generating short (<4 cm), sparse vegetation on recent burns. Although cattle selectively grazed recent burns, this did not alter vegetation structure in unburned portions of patch-burned pastures relative to controls. Of the 6 grassland bird species we examined, mountain plovers (Charadrius montanus) occurred exclusively on recent burns, whereas grasshopper sparrows (Ammodramus savannarum) occurred exclusively in grassland not burned for ≥3 years. Two species (lark bunting [Calamospiza melanocorys] and western meadowlark [Sturnella neglecta]) were 2–3 times less abundant on recent burns compared to controls, whereas densities of horned larks (Eremophila alpestris) and McCown's longspur (Rhynchophanes mccownii) were unaffected by burning. Lark bunting, western meadowlark, and grasshopper sparrow densities varied substantially among years. In the years when they were abundant, all 3 species increased in density across the time-since-burning gradient. Consistent with this pattern, patch-burn grazing management reduced the abundance of all 3 species at the whole-pasture scale. We found no evidence that unburned patches within the patch-burned pastures differed from unburned pastures in terms of the abundance of any bird species. Patch-burn grazing management was an effective strategy to create breeding habitat for mountain plovers. However, our findings suggest that in the shortgrass steppe, additional strategies that generate taller, more dense vegetation than occurs under moderate cattle grazing need to be considered in combination with patch-burn grazing management to sustain breeding habitat for the full suite of native grassland birds. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Habitat use by grassland birds in natural areas and soybean fields in southern Brazil and Uruguay

Livestock production and the replacement of semi-natural grasslands by crops result in land use changes and as consequence some habitat is no longer suitable for all species of grassland birds. Although some generalist species could benefit from such changes, habitat alteration is detrimental to the populations of most sensitive species. In this study, we investigated the patterns of habitat use by breeding grassland birds through the assessment of their presence/absence and abundance in a landscape composed of semi-natural grasslands and croplands in southern Brazil and Uruguay. We sampled grassland birds in 160 100-m radius point counts: 80 in a semi-natural grassland dominated landscape and 80 in soybean fields with grassland patches. We classified vegetation cover on a 100-m radius buffer following three classes of land use: semi-natural grasslands, wet grasslands, and soybean fields. We used GLMM to analyze presence/absence and abundance of grassland birds found in the region. Nine species showed a positive response to the semi-natural grasslands and/or wet grassland vegetation cover categories. Five species recorded are of conservation concern. Most of the grassland bird species preferred sites with high semi-natural grassland cover and only one species used primarily soybean fields. Grassland birds required around 80% of semi-natural grassland cover to maintain larger abundances. Research across landscapes and a better understanding of the responses of grassland birds to habitat modification are still needed to establish conservation practices of natural grasslands and their avifauna in southern Brazil and Uruguay.

The importance of range edges for an irruptive species during extreme weather events

Threats to wildlife species from extreme events, such as droughts, are predicted to increase in frequency and magnitude with climate change. Extreme events can cause mortality and community-level changes, but for some mobile species, movement away from areas affected may be a viable option. We examined the effect of extreme weather on spatial patterns of abundance for an irruptive grassland bird species, the Dickcissel (Spiza americana). We calculated route-level annual abundances and abundance anomalies from 1980 to 2012 from North American Breeding Bird Survey data, and classified the Dickcissel’s range into core and edge regions using these abundances. We then compared abundances in the core and edge regions to the standardized precipitation evapotranspiration index, a measure of drought, in linear regressions. We found that Dickcissel irruptions in the northern range edges were related to drought conditions in the range core, potentially a consequence of birds being ‘pushed’ to the range edge when weather was unsuitable. Specifically, Dickcissels moved into refuge sites containing a high proportion of cultivated crops, with higher vegetation greenness, than those areas they leave during drought years. In a changing climate where more frequent extreme weather may be more common, conservation strategies for weather-sensitive species may require consideration of habitat in the edges of species’ ranges, even though non-core areas may be unoccupied in ‘normal’ years. Our results highlight the conservation importance of range edges in providing refuge from extreme events, such as drought, and climate change.

The Potential Impacts of Saltcedar Eradication (Tamarix sp.) on the Birds of the Cimarron National Grassland

Saltcedar (Tamarix sp.) is a non-native woody invasive species that reduces groundwater supplies. Natural resource agencies and private landowners are seeking to eradicate this exotic species from watersheds in western Kansas, including from along the Cimarron River on the Cimarron National Grasslands. Our research studied the effects of saltcedar eradication on species richness and abundance of avian populations in riparian habitats. Nine, 500-m transects were established. Three were located in areas of dense saltcedar, three were in treated areas where saltcedar had been removed, and three were in areas dominated by cottonwood (Populus deltoides). For four consecutive years (2006–2009), each of the nine transects was walked twice during the typical avian breeding season (22 May to 5 July). The number of individuals for each bird species seen or heard within 50 m of the 500-m transect line was recorded. Twenty-seven bird species were found to be nesting in saltcedar. Saltcedar eradication efforts may negatively impact local populations of these species. Yellow-breasted Chat (Icteria virens), Field Sparrow (Spizella pusilla), and Indigo Bunting (Passerina cyanea) were found only in saltcedar-encroached areas and therefore may be particularly negatively affected by saltcedar removal. The removal of the woody vegetation created more grassland habitat thereby potentially benefiting the seven species of grassland birds found exclusively in the treated areas. Riparian areas dominated by cottonwood had the highest species richness with 36 species found, including 14 species that were found only in these areas. If successful, the current efforts of the US Forest Service (USFS) to establish and maintain cottonwood forest along the Cimarron River likely will result in significantly increased avian species richness.

Greater prairie‐chicken brood‐site selection and survival in the Nebraska sandhills

ABSTRACTThe greater prairie‐chicken (Tympanuchus cupido pinnatus) is a grassland bird species of conservation concern, although the region of the Nebraska Sandhills has the largest and most stable population in North America. The Sandhills region is semiarid and dominated by privately owned rangeland; vegetation in the region is typically less dense than the tall grass ecosystem. Most management recommendations for the greater prairie‐chicken are based on work in tall grass prairies, so our goal was to estimate the responses of brood‐site selection and survival to the unique vegetation characteristics of the Sandhills region. We studied prairie‐chickens on private rangelands in Rock and Brown Counties from 2009 to 2011. We radio‐marked 139 females and monitored females with broods from May through July using pickup‐mounted and handheld telemetry systems. We used discrete choice models to assess micro‐scale habitat selection within used pastures. Specifically, we investigated the effect of local heterogeneity of vegetation structure and composition on site selection. The contiguous grasslands of the Sandhills contain variation in soils, slope, and proximity to water table, so we also assessed selection of these ecological sites (the equivalent of land‐use categories in fragmented landscapes) for brood‐rearing within the broad landscape (macro‐scale). Last, we assessed variation in brood survival in response to weather and vegetation structure and composition. Prairie‐chicken females with broods selected sands ecological sites (upland, rolling hills sites) that had thicker vegetation with higher visual obstruction reading (VOR; = 7.7 cm, SE = 0.4), more variable VOR ( = 20.1, ±2.1), and greater litter depth ( = 0.07 cm, ±0.01) than at coupled random locations (VOR: = 6.6 cm, ±0.1; variance VOR: = 15.6, ±0.8; litter depth: = 0.05 cm, ±0.01). The selection function for brood sites peaked for sites with approximately 10 cm VOR, which was significantly less than the range of 20–30 cm of visual obstruction suggested for management of tallgrass prairies. In fact, only 5.0% of random sites and 5.4% of sites used by hens with broods had VOR &gt;20 cm. However, VOR and litter depth did not explain variability in brood survival, and we found considerable uncertainty in our analysis of daily survival. Models with forb cover were ranked highest in the survival analyses (combined ωAIC c = 0.63), which provided some support for a positive effect of forb cover on brood survival (βforb cover = 0.327, SE = 0.337). We suggest that land managers in the Sandhills region provide brooding habitat in grazed, upland ecological sites that is characterized by minimal bare ground, a consistent distribution of litter, a forb component, and VOR levels of 4–11 cm in pastures in the vicinity of leks. © 2015 The Wildlife Society.

Avian Use of Black-Tailed Prairie Dog Colonies in Shortgrass Prairie

Downward trends in populations of many grassland bird species are of conservation concern. Declines in black-tailed prairie dog ( Cynomys ludovicianus ) populations result in loss of habitat for birds and other species associated with their colonies. We measured abundance, diversity, and species composition of avian communities on prairie dog colonies and noncolony sites in the Texas Panhandle. More resident species ( P &lt; 0.001) occurred on prairie dog colonies than on noncolony areas whereas, more nearctic-neoptropical migrants ( P = 0.003) and nearctic-temperate migrants ( P &lt; 0.001) occurred on noncolony sites. Total avian abundance was greater ( P &lt; 0.001) on noncolony sites than at prairie dog colonies, and differed by season ( P &lt; 0.001). Barn swallows ( Hirundo rustica ), red-winged blackbirds ( Agelaius phoeniceus ), horned larks ( Eremophila alpestris ), and chipping sparrows ( Spizella passerina ) were more abundant on noncolony sites than on prairie dog colonies. Burrowing owl ( Athene cunicularia ), Cassin’s sparrow ( Peucaea cassinnii ), and lark bunting ( Calamospiza melanocorys ) abundances were greater on prairie dog colonies. Vegetative alterations made by prairie dogs may not influence bird populations as much in these shortgrass prairies as has been reported in mixed-grass prairies.

Do natural areas in urban landscapes support successful reproduction by a group of conservation priority birds?

AbstractIf conservation priority birds are to persist in an increasingly anthropogenically altered world, suitable habitat must be created or preserved in potentially unsuitable landscapes. While natural areas in urban environments may provide habitat for declining groups of birds, little is known about effects of urbanization on the reproductive success of birds, such as grassland birds, that are typically thought to be associated with more rural landscapes. While typical conservation efforts have focused on conserving large patches of grassland in landscapes containing minimal amounts of woody vegetation and development, the assumption that habitat located in developed landscapes is of poor quality has not been tested and may wrongly devalue grasslands located in an urban matrix. To examine the influence of development on habitat quality for grassland birds, we studied grassland bird nest predation and brood parasitism in patches of varying size along an urbanization gradient in northeastern Illinois. Because nest predation is the primary cause of reproductive failure and a potentially limiting factor for grassland bird populations, we used miniature video cameras to identify predators at a subset of nests. From 2012 to 2013, we monitored 432 nests of 16 grassland bird species. Nest predation rates decreased with urbanization in the landscape as did probability of brood parasitism. We filmed 44 nests and documented 19 predation events. We found that coyotes Canis latrans, white‐tailed deer Odocoileus virginianus and thirteen‐lined ground squirrels Ictidomys tridecemlineatus were important nest predators in our study system. Contrary to prior assumptions, our results suggest that grasslands located in urban landscapes may provide habitat of equal or greater quality than many rural grasslands.

Edge Effects on Avian Diversity and Density of Native Grass Conservation Buffers

Conservation Reserve Program Conservation Practice 33 (CP33: Conservation Buffers for Upland Birds) provides habitat for grassland birds in agriculture-dominated landscapes. However, landscape context and adjacency of other land covers may influence colonization, occupancy, and reproductive performance of breeding grassland birds in buffers. Our objective was to determine how edge effects influence diversity and density of breeding grassland birds in CP33 buffers. Data collected during transect surveys in CP33 buffers at a privately-owned farm in Clay County, Mississippi, USA during the 2007􀀁2009 breeding seasons indicated that buffers with a woody edge had the least diversity and density of grassland and facultative grassland birds. Dickcissels (Spiza americana), the most abundant grassland bird species detected in buffers, had a lower density in woodland-bordered buffers than in grassland-bordered buffers. Red-winged Blackbirds (Agelaius phoeniceus) had a lower density in buffers adjacent to woodlands than buffers adjacent to developed areas and those bordered on both sides by crop fields. Conversely, Indigo Buntings, (Passerina cyanea) a woodland edge species, had the greatest density in woodland-bordered buffers when compared to buffers adjacent to grassland and developed areas. These results demonstrate that adjacency influences colonization processes and conservation design should explicitly incorporate local landscape context in field and farm-scale conservation plans. Where conservation of obligate grassland birds is a primary objective of native grass conservation buffers, avoidance of buffer establishment adjacent to woodlands may maximize environmental services as measured by grassland bird diversity and density.

Bird Communities and Biomass Yields in Potential Bioenergy Grasslands

Demand for bioenergy is increasing, but the ecological consequences of bioenergy crop production on working lands remain unresolved. Corn is currently a dominant bioenergy crop, but perennial grasslands could produce renewable bioenergy resources and enhance biodiversity. Grassland bird populations have declined in recent decades and may particularly benefit from perennial grasslands grown for bioenergy. We asked how breeding bird community assemblages, vegetation characteristics, and biomass yields varied among three types of potential bioenergy grassland fields (grass monocultures, grass-dominated fields, and forb-dominated fields), and assessed tradeoffs between grassland biomass production and bird habitat. We also compared the bird communities in grassland fields to nearby cornfields. Cornfields had few birds compared to perennial grassland fields. Ten bird Species of Greatest Conservation Need (SGCN) were observed in perennial grassland fields. Bird species richness and total bird density increased with forb cover and were greater in forb-dominated fields than grass monocultures. SGCN density declined with increasing vertical vegetation density, indicating that tall, dense grassland fields managed for maximum biomass yield would be of lesser value to imperiled grassland bird species. The proportion of grassland habitat within 1 km of study sites was positively associated with bird species richness and the density of total birds and SGCNs, suggesting that grassland bioenergy fields may be more beneficial for grassland birds if they are established near other grassland parcels. Predicted total bird density peaked below maximum biomass yields and predicted SGCN density was negatively related to biomass yields. Our results indicate that perennial grassland fields could produce bioenergy feedstocks while providing bird habitat. Bioenergy grasslands promote agricultural multifunctionality and conservation of biodiversity in working landscapes.

Relatively high prevalence of pox-like lesions in Henslow's sparrow (Ammodrammus henslowii) among nine species of migratory grassland passerines in Wisconsin, USA.

Globally, Avipoxvirus species affect over 230 species of wild birds and can significantly impair survival. During banding of nine grassland songbird species (n=346 individuals) in southwestern Wisconsin, USA, we noted species with a 2-6% prevalence of pox-like lesions (possible evidence of current infection) and 4-10% missing digits (potential evidence of past infection). These prevalences approach those recorded among island endemic birds (4-9% and 9-20% for the Galapagos and Hawaii, respectively) for which Avipoxvirus species have been implicated as contributing to dramatic population declines. Henslow's Sparrow Ammodramus henslowii (n=165 individuals) had the highest prevalence of lesions (6.1%) and missing digits (9.7%). Among a subset of 26 Henslow's Sparrows from which blood samples were obtained, none had detectable antibody reactive to fowlpox virus antigen. However, four samples (18%) had antibody to canarypox virus antigen with test sample and negative control ratios (P/N values) ranging from 2.4 to 6.5 (median 4.3). Of four antibody-positive birds, two had lesions recorded (one was also missing a digit), one had digits missing, and one had no signs. Additionally, the birds with lesions or missing digits had higher P/N values than did the antibody-positive bird without missing digits or recorded lesions. This study represents an impetus for considering the impacts and dynamics of disease caused by Avipoxvirus among North American grassland bird species.

A multiscale assessment of tree avoidance by prairie birds

In North America, grassland bird abundances have declined, likely as a result of loss and degradation of prairie habitat. Given the expense and limited opportunity to procure new grasslands, managers are increasingly focusing on ways to improve existing habitat for grassland birds, using techniques such as tree removal. To examine the potential for tree removal to benefit grassland birds, we conducted 446 point counts on 35 grassland habitat patches in the highly fragmented landscape of west-central Minnesota during 2009–2011. We modeled density of four grassland bird species in relation to habitat composition at multiple scales, focusing on covariates that described grass, woody vegetation (trees and large shrubs), or combinations of grass and woody vegetation. The best-supported models for all four grassland bird species incorporated variables measured at multiple scales, including local features such as grass height, litter depth, and local tree abundance, as well as landscape-level measures of grass and tree cover. Savannah Sparrows (Passerculus sandwichensis), Sedge Wrens (Cistothorus platensis), and Bobolinks (Dolichonyx oryzivorus) responded consistently and negatively to woody vegetation, but response to litter depth, grass height, and grassland extent were mixed among species. Our results suggest that reducing shrub and tree cover is more likely to increase the density of grassland birds than are attempts to improve grass quality or quantity. In particular, tree removal is more likely to increase density of Savannah Sparrows and Sedge Wrens than any reasonable changes in grass quality or quantity. Yet tree removal may not result in increased abundance of grassland birds if habitat composition is not considered at multiple scales. Managers will need to either manage at large scales (80–300 ha) or focus their efforts on removing trees in landscapes that contain some grasslands but few nearby wooded areas.

Habitat availability is a more plausible explanation than insecticide acute toxicity for U.S. grassland bird species declines.

Grassland bird species have experienced substantial declines in North America. These declines have been largely attributed to habitat loss and degradation, especially from agricultural practices and intensification (the habitat-availability hypothesis). A recent analysis of North American Breeding Bird Survey (BBS) “grassland breeding” bird trends reported the surprising conclusion that insecticide acute toxicity was a better correlate of grassland bird declines in North America from 1980–2003 (the insecticide-acute-toxicity hypothesis) than was habitat loss through agricultural intensification. In this paper we reached the opposite conclusion. We used an alternative statistical approach with additional habitat covariates to analyze the same grassland bird trends over the same time frame. Grassland bird trends were positively associated with increases in area of Conservation Reserve Program (CRP) lands and cropland used as pasture, whereas the effect of insecticide acute toxicity on bird trends was uncertain. Our models suggested that acute insecticide risk potentially has a detrimental effect on grassland bird trends, but models representing the habitat-availability hypothesis were 1.3–21.0 times better supported than models representing the insecticide-acute-toxicity hypothesis. Based on point estimates of effect sizes, CRP area and agricultural intensification had approximately 3.6 and 1.6 times more effect on grassland bird trends than lethal insecticide risk, respectively. Our findings suggest that preserving remaining grasslands is crucial to conserving grassland bird populations. The amount of grassland that has been lost in North America since 1980 is well documented, continuing, and staggering whereas insecticide use greatly declined prior to the 1990s. Grassland birds will likely benefit from the de-intensification of agricultural practices and the interspersion of pastures, Conservation Reserve Program lands, rangelands and other grassland habitats into existing agricultural landscapes.

Assessing multiregion avian benefits from strategically targeted agricultural buffers.

Mounting evidence of wildlife population gains from targeted conservation practices has prompted the need to develop and evaluate practices that are integrated into production agriculture systems and targeted toward specific habitat objectives. However, effectiveness of targeted conservation actions across broader landscapes is poorly understood. We evaluated multiregion, multispecies avian densities on row-crop fields with native grass field margins (i.e., buffers) as part of the first U.S. agricultural conservation practice designed to support habitat and population recovery objectives of a national wildlife conservation initiative. We coordinated breeding season point transect surveys for 6 grassland bird species on 1151 row-crop fields with and without native grass buffers (9-37 m) in 14 U.S. states (10 ecoregions) from 2006 to 2011. In most regions, breeding season densities of 5 of 6 targeted bird species were greater in the 500-m surrounding survey points centered on fields with native grass buffers than in landscapes without buffers. Relative effect sizes were greatest for Northern Bobwhite (Colinus virginianus), Dickcissel (Spiza americana), and Field Sparrow (Spizella pusilla) in the Mississippi Alluvial Valley and Eastern Tallgrass Prairie regions. Other species (e.g., Eastern Meadowlark [Sturnella magna], Grasshopper Sparrow [Ammodramus savannarum]) exhibited inconsistent relative effect sizes. Bird densities on fields with and without buffers were greatest in the Central Mixed-grass Prairie region. Our results suggest that strategic use of conservation buffers in regions with the greatest potential for relative density increases in target species will elicit greater range-wide population response than diffuse, uninformed, and broadly distributed implementation of buffers. We recommend integrating multiple conservation practices in broader agricultural landscapes to maximize conservation effectiveness for a larger suite of species.

Rolling Pampas agroecosystem: which landscape attributes are relevant for determining bird distributions?

Agricultural intensification is among the main factors affecting biodiversity. The Rolling Pampas of Argentina have undergone through a process of landscape transformation and agricultural intensification that altered avian diversity patterns. Grassland area loss is argued to be the main reason for grassland bird species declines, but there is a lack of studies that compare cropland vs. pastures including other landscape features as determinants of species richness and distribution. Also, it is needed to understand how these relations are modified at different spatial scales. In this study, we explored how species are associated to different landscape attributes and elements like land use, roadside vegetation, trees, homesteads, and water bodies. Our aim was to explore how bird species are associated to the new elements of the Pampas agroecosystem at different spatial scales to reveal which are important for avian management. We ran field surveys covering a range of land use and landscape complexity, defined by the variety of component features. We performed canonical correspondence and diversity partition analyses to determine the association of species with land use, landscape complexity, and particular anthropogenic elements. Our results show that land use type is an important driver of bird species distributions, but it is also controlled by the presence of trees, houses, and water bodies that provide nesting and food resources. Simple landscapes have higher species turnover rates (beta diversity) than complex ones with similar gamma diversity, demonstrating that the effect of landscape simplification on bird diversity differs across spatial scales, leading to different possible management and conservation strategies. New approaches are needed to manage agroecosystems for avian conservation. We need to take pragmatic approaches, and in highly disturbed ecosystems, anthropic elements have to be included as constituent parts of the system.