Breeding Grassland Birds Research Articles

Contrasting effects of eucalyptus, pine and oak plantations on nest predation risk in Mediterranean grasslands

Large scale afforestation (i.e., establishment of forests on farmland, grassland and other land not previously forested) is increasingly regarded as a cost-effective option to mitigate climate change by promoting carbon sequestration. However, this strategy can have negative biodiversity impacts, potentially causing the loss and fragmentation of open habitats of conservation value, as well as edge effects that can extend well beyond forest boundaries. Mitigating impacts of afforestation programs thus requires a detailed understanding of the mechanisms whereby they affect biodiversity, particularly where new plantations are established close to areas important for open habitat species. Here, we examined how afforestation with oak, pine or eucalyptus trees, commonly planted in Mediterranean Europe, may have distinct effects on nest predation risk of grassland birds in southern Portugal. We used artificial nests with quail eggs and camera traps to: (i) identify nest predators and estimate predation risk of ground-nesting birds in grasslands adjacent to oak, pine and eucalyptus plantations across a distance gradient (0 m to 300 m) from the plantation edge; and (ii) examine how predation risk was influenced by avian predator abundance, sward height and vegetation clearing for photo-monitoring (nest-site manipulation), and their interactions with plantation type. Carrion crow was by far the main egg predator identified, followed by Montagu’s harrier, raven and magpie. Overall, nest predation risk and predator abundance were higher around eucalyptus plantations, compared to either pine or oak plantations. Predation decreased with increasing sward height, but this effect was less noticeable when vegetation around nests was cleared. In pine and oak plantations, predation risk was slightly higher close to edges, and decreased with distance from the edge. Conversely, in eucalyptus plantations predation was lower close to edges, and increased with distance to edges. Distance effects around eucalyptus plantation were, however, absent in manipulated nests. Overall, results show that afforestation with different tree species has distinct impacts on predation risk of artificial nests in Mediterranean farmland. This is probably a consequence of an increasing structural complexity of the plantations, from oak to eucalyptus, driven by differences in tree growth rates and undergrowth cover. These findings suggest that farmland afforestation should favour agro-forest plantations with slow growing species (oak and pine) to mitigate negative effects on breeding grassland birds in adjacent open habitats.

Limited Land Base and Competing Land Uses Force Societal Tradeoffs When Siting Energy Development

AbstractAs human populations grow, decisions regarding use of the world's finite land base become increasingly complex. We adopted a land use–conflict scenario involving renewable energy to illustrate one potential cause of these conflicts and resulting tradeoff decisions. Renewable energy industries wishing to expand operations in the United States are limited by multijurisdictional regulations in finding developable land. Interest groups entreat industries to avoid land for various reasons, including avoidance of prime wildlife habitat in accordance with an “avoidance-first” mitigation strategy. By applying a uniform set of rules for renewable energy facilities to the Prairie Pothole Region and portions of the Northern Great Plains, we evaluated the effects of regulations and avoidance of prime wildlife habitat on the amount of land available for development. In our scenario, existing regulations excluded 39% of the project area from potential development, with human infrastructure accounting for 30% (10–66% among states), whereas federally protected species accounted for < 1% at project area and state levels. Unregulated lands accounted for 61% of the project area, with conservation areas predicted as high-quality sites for breeding grassland birds and waterfowl and for migrating whooping cranes Grus americana accounting for 19% within the project area (6–27% among states). This model demonstrated a limited land base available for new development when accounting for regulations and concerns of a subset of societal interest groups. Additional interest groups likely will have different and competing concerns, further emphasizing the complexity of future land-use decisions as the available land base for development diminishes.

Plant invasions alter settlement patterns of breeding grassland birds

AbstractAnimals have evolved strategies to identify areas that provide the resources and environmental conditions they need to survive and reproduce. To explore how invasions by nonnative plants might disrupt this fundamental process, we evaluated settlement patterns of migratory birds that breed in grasslands being invaded by two structurally different congeneric grasses. We established 40, 2.25‐ha plots across an area where the composition of each nonnative grass ranged from 0% to nearly 100% of total grass cover, which provided individuals with the full range of alternatives in species composition. We then used the temporal sequence by which birds established territories to infer their habitat preferences. We evaluated responses of the most common species that settled the area, two confamilial sparrows that differed markedly in habitat breadth. The species with narrower habitat breadth, the grasshopper sparrow (Ammodramus savannarum ammolegus), first established territories in areas dominated by native grasses, where grass height and cover were substantially lower than in areas dominated by the nonnative grasses. As the settlement period progressed, they increasingly established territories in areas dominated by the smaller nonnative grass (Eragrostis lehmanniana), but never established territories in areas dominated by the larger grass (E. curvula). In contrast, the species with broader habitat breadth, the Botteri's sparrow (Peucaea botterii arizonae), established territories without regard to grass composition, likely because both nonnative grasses were within the structural range of native grasses used by this grassland generalist. Our results demonstrate that in areas invaded by nonnative plants, changes in habitat use by animals can reflect the interaction between their habitat breadth and the amount of structural contrast between invading plants and the native plant species that are displaced. This interaction provides a mechanism to explain the variation in responses among species to invasions by nonnative plants, which has consequences for broad‐scale changes in the geographic distribution of many species.

Adaptive rangeland management benefits grassland birds utilizing opposing vegetation structure in the shortgrass steppe.

Rangelands are temporally and spatially complex socioecological systems on which the predominant land use is livestock production. In North America, rangelands also contain approximately 80% of remaining habitat for grassland birds, a guild of species that has experienced precipitous declines since the 1970s. While livestock grazing management may benefit certain grassland bird species by generating the vegetation structure and density they prefer, these outcomes are poorly understood for avian species breeding in the shortgrass steppe. We evaluated how two grazing management systems, continuous, season-long grazing and adaptive, rest-rotational grazing, affected grassland bird abundance from 2013 to 2017 in Colorado's shortgrass steppe. We examined grazing impacts in conjunction with ecological sites, which constitute unique soil and plant communities. When grazing management was evaluated in conjunction with spatial variation in ecological sites, we found three of our five focal bird species responded to grazing management. McCown's Longspur abundance decreased in pastures rested from grazing the previous year. The effect of grazing on Horned Lark and Grasshopper Sparrow depended on ecological site: Horned Lark density was highest in pastures that were intensively grazed and Grasshopper Sparrow density was highest in pastures that were rested the previous year in the least productive ecological site. In addition, densities of all species varied across ecological sites. Our results suggest consideration of soil and vegetation characteristics can inform how adaptive management is applied on a landscape to benefit the full suite of breeding grassland birds, including species that have seemingly contrasting habitat needs. For example, a manager could target adaptive drought mitigation practices, such as resting pastures for 1 yr to generate grassbanks, in less productive soils to benefit grassland birds that prefer taller/denser vegetation structure, or could apply intensive, short-duration grazing on less productive soils to benefit species preferring shorter/sparser vegetation. A single year of intensive, short-duration grazing (i.e., one component of our rotational treatment) across the landscape, however, might not create sufficient habitat for species that prefer short/sparse vegetation in our system (e.g.,McCown's Longspur). Ultimately, our study indicates how cattle production on rangelands can congruently support grassland bird populations in the shortgrass steppe.

Conservation of breeding grassland birds requires local management strategies when hay maturation and nutritional quality differ among regions

Early hay harvest can negatively affect grassland bird reproduction. Agriculturists may delay harvest in support of grassland bird conservation if hay quality is not jeopardized. We examined changes in hay quality over time at three latitudes in Ontario, and for the central region, we related results to bobolink (Dolichonyx oryzivorus) breeding phenology. We collected hay samples at all latitudes from 1 June through 16 July and quantified changes in percent crude protein (CP), acid detergent fibre (ADF), calcium (Ca) and phosphorus (P). At the same time, we also monitored breeding behaviour of all grassland birds but sufficient data for analyses and comparative purposes were collected only for bobolinks in central Ontario. Most Ontario hayfields sampled were low in energy and digestibility throughout the growing season (mean ADF values>35%). Ca levels were more than adequate for most livestock but P supplementation may be required depending on the production goals of the farmer. Crude protein levels were higher in forage samples collected from northern study plots and fell below 10% one week later than in central and southern Ontario. In central Ontario, CP levels were highest in the first week of June (12–15%). In the last two weeks of June through to mid-July, mean CP levels dropped from 11% to 9.5%, roughly 0.5% per week. Fledgling bobolinks were first observed on 14 and 16 June; they were counted in larger numbers after 20 June and reached a peak 1–14 July. A delayed hay harvest (mid-July) in this region would support bobolink reproduction without compromising forage quality for a variety of livestock enterprises. Timing of hay harvest to benefit grassland birds in regions to the north and south may differ depending on local geologic and climatic conditions and breeding bird behaviour. Based on our results, farmers that opt to manage their hayfields in support of grassland birds can delay the timing of hay harvest with trade-offs not as severe as once thought. The delayed hay harvest strategy may have wider applications to agro-ecosystems globally; its feasibility would only require knowledge of local breeding bird activity and forage quality over time.

Interpreting failure to reject the null hypothesis of displacement from wind turbines in three species of grassland birds: Response to Johnson (2016)

ABSTRACT Johnson (2016) criticized our 3-year study investigating displacement in breeding grassland birds at an operational wind facility in the southern Great Plains. Although Johnson characterized our statistical methods as inappropriate and our study as intentionally misleading, his claims are based on his own view of the appropriate analysis and interpretation. Although we failed to reject the null hypothesis of no displacement in breeding grassland birds at our study site, the main message of our manuscript was a cautionary tale—that is, that at many wind facilities it will be difficult to isolate the effect of distance to turbine from other factors that covary with distance.

Effects of wind‐energy facilities on breeding grassland bird distributions

The contribution of renewable energy to meet worldwide demand continues to grow. Wind energy is one of the fastest growing renewable sectors, but new wind facilities are often placed in prime wildlife habitat. Long-term studies that incorporate a rigorous statistical design to evaluate the effects of wind facilities on wildlife are rare. We conducted a before-after-control-impact (BACI) assessment to determine if wind facilities placed in native mixed-grass prairies displaced breeding grassland birds. During 2003-2012, we monitored changes in bird density in 3 study areas in North Dakota and South Dakota (U.S.A.). We examined whether displacement or attraction occurred 1 year after construction (immediate effect) and the average displacement or attraction 2-5 years after construction (delayed effect). We tested for these effects overall and within distance bands of 100, 200, 300, and >300 m from turbines. We observed displacement for 7 of 9 species. One species was unaffected by wind facilities and one species exhibited attraction. Displacement and attraction generally occurred within 100 m and often extended up to 300 m. In a few instances, displacement extended beyond 300 m. Displacement and attraction occurred 1 year after construction and persisted at least 5 years. Our research provides a framework for applying a BACI design to displacement studies and highlights the erroneous conclusions that can be made without the benefit of adopting such a design. More broadly, species-specific behaviors can be used to inform management decisions about turbine placement and the potential impact to individual species. Additionally, the avoidance distance metrics we estimated can facilitate future development of models evaluating impacts of wind facilities under differing land-use scenarios.

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.

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.

Habitat and landscape effects on abundance of Missouri's grassland birds

AbstractOf 6 million ha of prairie that once covered northern and western Missouri, <36,500 ha remain, with planted, managed, and restored grasslands comprising most contemporary grasslands. Most grasslands are used as pasture or hayfields. Native grasses largely have been replaced by fescue (Festuca spp.) on most private lands (almost 7 million ha). Previously cropped fields set aside under the Conservation Reserve Program (CRP) varied from a mix of cool‐season grasses and forbs, or mix of native warm‐season grasses and forbs, to simple tall‐grass monocultures. We used generalized linear mixed models and distance sampling to assess abundance of 8 species of breeding grassland birds on 6 grassland types commonly associated with farm practices in Missouri and located in landscapes managed for grassland‐bird conservation. We selected Bird Conservation Areas (BCAs) for their high percentage of grasslands and grassland‐bird species, and for <5% forest cover. We used an information‐theoretic approach to assess the relationship between bird abundance and 6 grassland types, 3 measures of vegetative structure, and 2 landscape variables (% grassland and edge density within a 1‐km radius). We found support for all 3 levels of model parameters, although there was less support for landscape than vegetation structure effects likely because we studied high‐percentage‐grassland landscapes (BCAs). Henslow's sparrow (Ammodramus henslowii) counts increased with greater percentage of grassland, vegetation height‐density, litter depth, and shrub cover and lower edge density. Henslow's sparrow counts were greatest in hayed native prairie. Dickcissel (Spiza americana) counts increased with greater vegetation height‐density and were greatest in planted CRP grasslands. Grasshopper sparrow (A. savannarum) counts increased with lower vegetation height, litter depth, and shrub cover. Based on distance modeling, breeding densities of Henslow's sparrow, dickcissel, and grasshopper sparrow in the 6 grassland types ranged 0.9–2.6, 1.4–3.2, and 0.1–1.5 birds/ha, respectively. We suggest different grassland types and structures (vegetation height, litter depth, shrub cover) are needed to support priority grassland‐bird species in Missouri. © 2011 The Wildlife Society.

Influences of Management Regimes on Breeding Bird Densities and Habitat in Mixed-Grass Prairie: An Example from North Dakota

It is well known that North American grassland bird populations appear to be declining (Igl and Johnson 1997, Sauer et al. 2004). Most of these birds breed and winter in North America, so declines are likely associated with continental processes (Knopf 1994). Scientists have also observed parallel declines among species that have overlapping breeding ranges but disparate wintering distributions (Igl and Johnson 1997). These patterns suggest declines may be linked to problems on the breeding grounds. Across the Great Plains, the breeding grounds for many of these species, one primary land-use is grazing by domestic cattle. Before European settlement, most of this region was grazed by freeranging herbivores, particularly bison (Hartnett et al. 1997). With settlement, bison were mostly extirpated from the region, and cattle grazing systems were established. This species replacement may have transformed the landscape because bison and cattle grazing regimes differ somewhat (Harnett et al. 1997). Bison and cattle possess slightly different foraging preferences and patterns (Hartnett et al. 1997), and cattle herds are spatially constrained whereas historic bison herds roamed freely (Steuter and Hidinger 1999). Moreover, grassland fire is usually suppressed and rarely prescribed in modern cattle-managed systems, yet during the time of the bison, naturally occurring fires burned at varying frequencies in the Great Plains (Steuter and Hidinger 1999). Today, some land managers are trying to reestablish this ecological condition by reintroducing smaller bison herds to various locations in the region, along with prescribed fire (Hartnett et al. 1997, Griebel et al. 1998). Given this recent trend, it is an opportune time to compare how a widespread, modern land-management regime and a re-created historic regime affect breeding grassland birds. Only Zimmerman (1997) and Griebel et al. (1998) have compared effects of bison and cattle grazing regimes on birds, in tallgrass prairie and sandhills prairie, respectively. Moreover, only Griebel et al. (1998) studied the effects of a bison regime that included fire. Thus, our study is the first to compare effects of these regimes in mixed-grass prairie. Of these 3 studies, ours is also unique because we estimate bird densities using distance sampling. We evaluated bird population densities and their habitats under cattle and bison management regimes in mixedgrass prairie. Our objectives were to 1) determine the influence of these different range-management regimes on habitat structure, composition, and heterogeneity; and 2) determine whether bird breeding densities differ between regimes.

GRASSLAND BIRD USE OF RIPARIAN FILTER STRIPS IN SOUTHEAST IOWA

The U.S. Department of Agriculture (USDA) under its Continuous Enrollment Conservation Reserve Program (CRP) has actively promoted establishment of conservation buffers. Although these programs are intended to benefit wildlife in addition to protecting soil and water resources, benefits to grassland birds may be compromised by narrow widths, presence of woody vegetation, and high predation pressure. During 2001 and 2002, we surveyed breeding grassland birds and searched for nests in 33 CRP filter strips that varied in planting mixture (cool-season vs. warm-season grasses) and adjacent edge type (non-wooded vs. wooded). The most abundant species in filter strips were red-winged blackbird (Agelaius phoeniceus), dickcissel (Spiza americana), song sparrow (Melospiza melodia), and common yellowthroat (Geothlypis trichas). Relative abundances of birds and nests were similar between cool-season and warm-season planting mixtures. Dickcissels and red-winged blackbirds and their nests were relatively less abundant at wooded than non-wooded sites. Our nest success estimates generally were low in all treatments, and nest success varied little with the variables we studied. Predation was the major cause of nest failure; 62% of all nests were depredated. Although the most common birds using filter strips are generalists, filter strips also have potential to provide breeding habitat for some species of management concern.

Tree and shrub invasion in northern mixed-grass prairie: implications for breeding grassland birds

North American grasslands continue to decline in quantity and quality. In the northern mixed-grass prairie, potential edge and fragmentation effects on grassland birds are poorly understood and conclusions are based largely on data from outside the region. Lands in and adjacent to J. Clark Salyer National Wildlife Refuge in north-central North Dakota comprise one of the largest contiguous patches of northern mixed-grass prairie remaining in North America. However, within the region, aspen (Populus tremuloides), willow (Salix spp.), and other woody species have increased, such that continued existence of grasslands is threatened. We examined how breeding grassland birds responded to habitat that has been variably fragmented by encroaching woody vegetation. The probability of occurrence decreased markedly for 11 of 15 bird species (including 3 endemic to the northern Great Plains) as percent woodland, tall shrub, or brush cover increased. Bird species were increasingly affected as the height of woody plants increased from brush to tall shrubs to trees. Grasslands became largely unsuitable for 9 species as woodland cover exceeded 25%. Derived models can be used by land managers to predict the outcome of management actions that alter plant community succession or that restore grasslands degraded by woody invasion.

Habitat and Landscape Associations of Breeding Birds in Native and Restored Grasslands

In the midwestern United States, less than 1% of the original tallgrass prairie ecosystem remains. State and federal agencies have responded to this habitat loss with programs and land acquisition that have increased the amount of grassland on the landscape by restoring grassland from other land-use practices. We assessed the effects of habitat restoration and the relative contribution of local habitat and landscape factors on breeding grassland birds in northern Iowa. During the 1999 and 2000 breeding seasons, we surveyed grassland birds in 10 tallgrass prairies and 10 restored grasslands that contained a wide diversity of habitat and landscape conditions. Densities of common bird species were similar between habitat types, except for grasshopper sparrows (Ammodramus savannarum) and savannah sparrows (Passerculus sandwichensis), which were 4 and 9 times more dense in restored grasslands, respectively. Species richness of breeding birds was similar between habitat types. Habitat structure was different in prairies and restored grasslands; restored grasslands had 7% less total vegetation cover and 3% more bare ground. A nested, multiscale analysis indicated that habitat structure explained some variation in species richness and bird density of all common species, yet addition of landscape structure improved models for species richness and for density of 4 of 8 species considered, explaining an additional 10-29% of the variation. Edge-density metrics were the most common variables entering into landscape models; most species had lower densities in landscapes with high edge density. Our results indicate that restored grassland habitats contain bird communities generally similar to those in native prairie habitats in northern Iowa, suggesting that restored grasslands may provide similar habitat suitability for most grassland birds. In addition, both local habitat and landscape factors can be important for managing breeding grassland birds.

Do Artificial Song-Perches Affect Habitat Use by Grassland Birds in Maine?

-To test the hypothesis that absence of song-perches limits use of habitat by breeding grassland birds, we placed artificial 1-m tall song-perches in two experimental plots in Maine. We found no evidence to support this hypothesis. Although these artificial songperches were used frequently as singing perches, species composition and territory densities on these plots were nearly identical to those found on two reference plots. Furthermore, we found no differences in territory densities between species that sing flight-songs and species that sing from fixed perches. Our results indicate that: (1) the absence of song-perches did not limit grassland birds at this site, and (2) that a variety of habitat parameters probably influence the habitat selection process. Thus, it appears unlikely that the long-term population declines reported for many species of grassland birds in eastern North America can be mitigated by simple measures such as adding artificial song-perches to grassland habitats. It is more likely that a variety of factors, possibly on both the breeding and wintering grounds, are involved in these long-term declines.

Prey Choice by Three Insectivorous Grassland Birds: Reevaluating Opportunism

Assemblages of breeding grassland birds have typically been considered dietary opportunists. We studied prey selection by an assemblage of three breeding insectivores grasshopper sparrows, lark sparrows, and western meadowlarks ― in the Sandhills grasslands of Nebraska, USA and we contrast three foraging models with a null model of opportunism. Handling times and %-chitin varied among prey taxa. The profitability (grams of non-chitin intake/handling time) of acridids, a major part of the diet of all three birds, declined with body size of grasshoppers. We measured Selectivities by comparing arthropods recovered from avian guts with those recovered from sweep sampling. Birds preferred some prey taxa (e.g., acridids, tettigoniids, small Coleoptera) over others (e.g., Homoptera, Hymenoptera, spiders)