Spiza Research Articles

The long shadow of woody encroachment: An integrated approach to modeling grassland songbird habitat.

Animals must track resources over relatively fine spatial and temporal scales, particularly in disturbance-mediated systems like grasslands. Grassland birds respond to habitat heterogeneity by dispersing among sites within and between years, yet we know little about how they make post-dispersal settlement decisions. Many methods exist to quantify the resource selection of mobile taxa, but the habitat data used in these models are frequently not collected at the same location or time that individuals were present. This spatiotemporal misalignment may lead to incorrect interpretations and adverse conservation outcomes, particularly in dynamic systems. To investigate the extent to which spatially and temporally dynamic vegetation conditions and topography drive grassland bird settlement decisions, we integrated multiple data sources from our study site to predict slope, vegetation height, and multiple metrics of vegetation cover at any point in space and time within the temporal and spatial scope of our study. We paired these predictions with avian mark-resight data for 8 years at the Konza Prairie Biological Station in NE Kansas to evaluate territory selection for Grasshopper Sparrows (Ammodramus savannarum), Dickcissels (Spiza americana), and Eastern Meadowlarks (Sturnella magna). Each species selected different types and amounts of herbaceous vegetation cover, but all three species preferred relatively flat areas with less than 6% shrub cover and less than 1% tree cover. We evaluated several scenarios of woody vegetation removal and found that, with a targeted approach, the simulated removal of just one isolated tree in the uplands created up to 14 ha of grassland bird habitat. This study supports growing evidence that small amounts of woody encroachment can fragment landscapes, augmenting conservation threats to grassland systems. Conversely, these results demonstrate that drastic increases in bird habitat area could be achieved through relatively efficient management interventions. The results and approaches reported pave the way for more efficient conservation efforts in grasslands and other systems through spatiotemporal alignment of habitat with animal behaviors and simulated impacts of management interventions.

Consequences of drought for grassland songbird reproduction

AbstractAbiotic stressors can be major sources of selection, resulting in diverse demographic responses operating via multiple direct and indirect mechanisms. However, unusual weather events are notoriously difficult to study due to their spatial and temporal unpredictability. A severe drought affected the Flint Hills of Kansas in 2018, occurring during the ongoing population‐level studies of three species of declining grassland songbirds: Eastern Meadowlarks (Sturnella magna), Grasshopper Sparrows (Ammodramus savannarum), and Dickcissels (Spiza americana). We compared nest survival, nest initiation date, and potential behavioral drivers of reproductive differences (i.e., nest orientation, investment) between the 2018 drought year and 2–6 years of average‐to‐wet years. Nest initiation in the drought year was concentrated early in the season, suggesting that birds did not renest or attempt second broods. The two species that build domed nests shifted the orientation of nest entrances away from early morning sun and toward the direction of prevailing winds in the drought year. Multiple nest‐level metrics of investment and success were similar in drought and nondrought years. These results suggest that demographic changes during droughts can reflect both direct responses and may also involve biotically mediated trophic consequences.

An efficient acoustic classifier for high‐priority avian species in the southern Great Plains using convolutional neural networks

AbstractPassive acoustic monitoring is a valuable ecological and conservation tool that allows researchers to collect data from vocal species across large geographic areas and temporal spans. Grassland bird populations, many of which are indicators of ecosystem health, have experienced precipitous declines over the past several decades. Acoustic monitoring of grassland bird populations provides opportunities to monitor declines and focus conservation practices, yet the ability to identify species efficiently and accurately from acoustic data is challenging. Therefore, development of automated classifiers such as convolutional neural networks (CNNs) are at the forefront of streamlining detection and identification of individual species. Here, we present a CNN classifier for 5 key grassland bird species across southcentral Oklahoma, a part of the southern Great Plains: northern bobwhite (Colinus virginianus), painted bunting (Passerina ciris), dickcissel (Spiza americana), eastern meadowlark (Sturnella magna), and Bell's vireo (Vireo bellii). We compiled a high‐quality training dataset consisting of 6,933 calls, built semiautonomously using template matching that can be expanded easily to any bird species of interest. Our trained multilabel CNN achieved a high level of classification accuracy (≥98%) for the 5 species using the library of test calls and field recordings played using a programmable game caller. The ability to conduct acoustic wildlife surveys across large spatial extents will allow for more efficient monitoring of wildlife to determine key population parameters and trends and effects of biotic and abiotic factors (e.g., vegetation, disturbance, weather) on these key species.

Long-term trends in grassland bird relative abundance on focal grassland landscapes in Missouri.

North American grassland birds have widely declined over the past 50 years, largely due to anthropogenic-driven loss of native prairie habitat. In response to these declines, many conservation programs have been implemented to help secure wildlife habitat on private and public lands. The Grasslands Coalition is one such initiative established to advance the conservation of grassland birds in Missouri. The Missouri Department of Conservation conducted annual point count surveys for comparison of grassland bird relative abundance between focal grassland areas and nearby paired (i.e., containing no targeted management) sites. We analyzed 17 years of point count data with a generalized linear mixed model in a Bayesian framework to estimate relative abundance and trends across focal or paired sites for nine bird species of management interest that rely on grasslands: barn swallow (Hirundo rustica), brown-headed cowbird (Molothrus ater), dickcissel (Spiza americana), eastern meadowlark (Sturnella magna), grasshopper sparrow (Ammodramus savannarum), Henslow's sparrow (A. henslowii), horned lark (Eremophila alpestris), northern bobwhite (Colinus virginianus), and red-winged blackbird (Agelaius phoeniceus). Relative abundance of all species except eastern meadowlarks declined regionally. Relative abundance of barn swallows, brown-headed cowbirds, dickcissels, eastern meadowlarks, Henslow's sparrows, and northern bobwhites was higher in focal than paired sites, though relative abundance trends were only improved in focal vs. paired areas for dickcissels and Henslow's sparrows. Relative abundance increased with increasing grassland cover at the local (250-m radius) scale for all species except horned larks and red-winged blackbirds and at the landscape (2,500-m radius) scale for all species except dickcissels, eastern meadowlarks, and northern bobwhites. Our results suggest focal areas contained greater relative abundances of several grassland species of concern, likely due to increased availability of grassland habitat at local and landscape scales. Further efforts to decrease landscape-scale fragmentation and improve habitat quality may be needed to achieve conservation goals.

Habitat suitability for Dickcissels (Spiza americana) during spring and fall migration: A species distribution modeling approach

IntroductionMigratory songbirds have experienced consistent population declines over the past half-century. An important, though often overlooked, contributor to these declines is the loss and degradation of stopover areas during migration, which are critical for allowing migrants to rest and refuel, and arrive in good condition at breeding and nonbreeding grounds.MethodsHere, we used publicly available eBird occurrence data to build species distribution models examining habitat suitability of the Dickcissel, a grassland-associated neotropical migrant, during spring and fall migration. Our models included variables representing land cover type, climate, and net primary productivity.ResultsLand cover variables were consistently better predictors of Dickcissel occurrence than climate or net primary productivity, suggesting that land cover type has a stronger impact on stopover habitat suitability than environmental factors. During spring migration, Dickcissel occurrence probability decreased with shrubland cover and precipitation seasonality. During fall migration, occurrence probability increased with proximity to water and human development, and decreased with increasing net primary productivity. We detected positive associations during both spring and fall with annual mean temperature and temperature seasonality, and a negative association with forest cover. Surprisingly, our models detected no strong associations with grassland or agriculture, despite the importance of these habitat types for Dickcissels during the breeding and nonbreeding seasons.DiscussionUltimately, our results suggest that Dickcissels exhibit greater flexibility when selecting stopover sites compared to breeding or nonbreeding areas, although their avoidance of forest and shrubland may indicate that they will be negatively impacted by further woody encroachment into open habitats across their migratory routes.

Three grassland bird species’ responses to fire and habitat structure in southern Illinois, USA suggest broad benefits of grassland size and plant diversity

Grassland birds are the most rapidly declining bird guild in North America, largely due to extensive habitat loss and fragmentation. Because many grassland bird species have different habitat preferences, managing grasslands to provide habitat for a range of species can be a challenge. We used four years of data from southern Illinois, USA grasslands to estimate the influence of prescribed fire and habitat structure on nest survival, nest density, and abundance of three grassland bird species with different habitat preferences: Dickcissel (<em>Spiza americana</em>), Field Sparrow (<em>Spizella pusilla</em>), and Common Yellowthroat (<em>Geothlypis trichas</em>). We found that Dickcissels exhibited the strongest response to prescribed fire, as nest density and nest survival both increased after previously undisturbed grasslands were burned. Fire may have also benefitted Common Yellowthroats and Field Sparrows by reducing woody cover and increasing bare ground, both of which were characteristics associated with nest survival for these birds. Dickcissel abundance was positively related to plant diversity within a grassland and agriculture in the surrounding landscape (within 400 m of a grassland patch), and negatively related to edge-interior ratio. Field Sparrows demonstrated a positive association with woody cover and proximity to forests. Common Yellowthroats were associated with tall vegetation and agriculture in the surrounding landscape. Both Field Sparrows and Common Yellowthroats associated positively with habitat characteristics that reduced nest survival, suggesting potential adaptive mismatches. Our results suggest that periodic prescribed fire, increased plant diversity, and larger patch size may simultaneously benefit a broad variety of grassland bird species with different habitat preferences.

Increased abundance and productivity of a grassland bird after experimental control of invasive tall fescue

Tall fescue (Schedonorus arundinaceus) is a widespread invasive grass in the United States that degrades habitat quality for biodiversity. Herbicide followed by seeding of native plants reduces tall fescue and is predicted to restore habitat quality over time, but little is known about short‐term (1–2 year) impacts on native species. We conducted a landscape‐scale controlled experiment to assess the short‐term effects of herbicide and seeding on the reproduction of an obligate grassland bird, the dickcissel (Spiza americana). In 2014, four sites in southern Iowa were each subdivided into three patches (mean 7 ha). One patch in each site was treated with glyphosate herbicide (spray‐only), one with herbicide and native seeding (spray‐and‐seed), with the third serving as a control. Two sites were grazed by cattle from April to July and two sites were ungrazed. We monitored dickcissel reproduction in 2016, finding that they were more abundant, built more nests, experienced less cowbird parasitism, had increased nest survival, and produced more fledglings on spray‐only and spray‐and‐seed treatments compared to control patches. Dickcissels nested infrequently on grazed sites—especially grazed control patches. We did not detect any impacts on clutch size, provisioning rates, or nestling mass, but Araneae (spiders) and Lepidoptera larvae (caterpillars) may have been smaller on sprayed patches. Positive responses by dickcissels were likely due to successful reduction of tall fescue and improved access to suitable nest sites through increased vegetation heterogeneity. Our results indicate that using herbicide and seeding to restore tall fescue‐dominated sites improves habitat quality for this grassland bird, shortly after restoration.

Cattle grazing in CRP grasslands during the nesting season: effects on avian abundance and diversity

AbstractThe Conservation Reserve Program (CRP) is a primary tool for restoring grassland in the United States, in part as wildlife habitat, which has benefited declining grassland bird populations. Among potential mid‐contract management practices used to maintain early‐successional CRP grasslands, cattle grazing had been prohibited and is currently disincentivized during the primary nesting season for birds (much of the growing season), despite the important role that large herbivores historically played in structuring grassland ecosystems. Conservative grazing of CRP grasslands could increase spatial heterogeneity in vegetation structure and plant diversity, potentially supporting higher densities of some grassland bird species and higher bird diversity. Our objective was to determine the effect of experimental cattle grazing on species‐specific relative abundance and occupancy, species diversity, and community dissimilarity of grassland birds on CRP grasslands across the longitudinal extent of Kansas, USA (a 63.5‐cm precipitation gradient) during the 2017–2019 avian breeding seasons. Fifty‐three of 108 fields were grazed by cattle during the growing seasons of 2017 and 2018 and all fields were rested from grazing in 2019. For all analyses, we examined separate model sets for semiarid western versus more mesic eastern Kansas. Using data from line transect surveys, we modeled relative abundances of 5 songbird species: grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), eastern meadowlark (Sturnella magna), western meadowlark (Sturnella neglecta), and brown‐headed cowbird (Molothrus ater). Grazing had delayed yet positive effects on abundances of grasshopper sparrow in western Kansas, and eastern meadowlark in eastern Kansas, but negative effects on dickcissel abundance in western Kansas and especially on burned fields in eastern Kansas. Somewhat counterintuitively, brown‐headed cowbirds in western Kansas were more abundant on ungrazed versus grazed fields in the years after grazing began. In addition, we modeled multi‐season occupancy of 3 gamebird species (ring‐necked pheasant [Phasianus colcicus], northern bobwhite [Colinus virginianus], mourning dove [Zenaida macroura]) and Henslow's sparrow (Centronyx henslowii); grazing did not affect occupancy of these species. In eastern Kansas, species diversity was highest in grazed, unburned fields. In western Kansas, bird communities in grazed and ungrazed fields were dissimilar, as determined from multivariate analysis. Though regionally variable, conservative stocking of cattle on CRP grasslands during the nesting season as a mid‐contract management tool might increase bird species diversity by restructuring habitat that accommodates a greater variety of species and decreasing abundances of species associated with taller, denser stands of vegetation.

Predation, parasitism, and drought counteract the benefits of patch-burn grazing for the reproductive success of grassland songbirds

Abstract Intensification of livestock production has reduced heterogeneity in vegetative structure in managed grasslands, which has been linked to widespread declines in grassland songbird populations throughout North America. Patch-burn grazing management aims to restore some of that heterogeneity in vegetative structure by burning discrete pasture sections, so that cattle preferentially graze in recently burned areas. Although patch-burn grazing can increase reproductive success of grassland songbirds, we know little about possible interactions with regional variation in predator communities or brood parasite abundance, or annual variation in weather conditions. Using six years of data from two tallgrass prairie sites in eastern Kansas, USA, we tested effects of patch-burn grazing on the rates of brood parasitism, clutch size, nest survival, and fledging success of three common grassland songbirds, Dickcissels (Spiza americana), Eastern Meadowlarks (Sturnella magna), and Grasshopper Sparrows (Ammodramus savannarum), among pastures managed with patch-burn grazing versus pastures that were annually burned and either grazed or ungrazed. Dickcissel nests experienced lower parasitism (72.8 ± 4.6% SE vs. 89.1 ± 2.2%) and Eastern Meadowlarks had higher nest survival (63.2 ± 20.5% vs. 16.5 ± 3.5%) in annually burned and ungrazed pastures than pastures managed with patch-burn grazing. However, average number of host fledglings per nesting attempt did not differ among management treatments for any species. Annual variation in weather conditions had a large effect on vegetation structure, but not on reproductive success. Probability of brood parasitism was consistently high (25.5‒84.7%) and nest survival was consistently low (9.9–16.9%) for all species pooled across treatments, sites, and years, indicating that combined effects of predation, parasitism and drought can offset potential benefits of patch-burn grazing management previously found in tallgrass prairies. Although differences in reproductive success among management treatments were minimal, patch-burn grazing management could still benefit population dynamics of grassland songbirds in areas where nest predators and brood parasites are locally abundant by providing suitable nesting habitat for bird species that require greater amounts of vegetation cover and litter, generally not present in burned pastures.

Results from Kentucky’s 10-year Bobwhite Recovery Plan

The northern bobwhite (Colinus virginianus; hereafter, bobwhite) has experienced a precipitous population decline through almost all its historical range over the last 6 decades. We initiated a 10-year restoration plan in Kentucky, USA in 2008 and reported on it through 3 published “Road to Recovery” reports along with 30 peer-reviewed articles and abstracts, 2 technical documents, 7 theses or dissertations, and 11 popular literature pieces. Seven Quail Focus Areas were selected across the state based on site personnel, geographic position (east to west), and land ownership (e.g., private, public, state, federal) for monitoring and habitat management. The focus areas averaged 11,895 acres and area managed for quail on an annual basis ranged from 9% to 42%. Management took the form of herbicide applications, disking, fire, planting, grazing, control of woody vegetation, and mowing. Hierarchical distance sampling models using time-of-removal information to inform detection processes were used to assess bobwhite density on each focus area. Models were based on spring breeding bird point counts in which a suite of grassland songbirds were recorded and fall covey counts in which only bobwhite were recorded. Roadside surveys (direct observation) and hunter harvest information were also used for statewide comparisons of focus areas and statewide trends. Across all years and focus areas a 40% increase in the quail population was observed in 20 years (38%) of the possible 53 years of survey data. Stable to increasing trends were also observed in focal area populations of dickcissel (Spiza americana), eastern meadowlark (Sturnella magna), eastern kingbird (Tyrannus tyrannus), field sparrow (Spizella pusilla), prairie warbler (Setophaga discolor), and Bell’s vireo (Vireo bellii). A focus on habitat management and associated monitoring on relatively small (<20,000 acres) areas was shown to be successful on an individual area, as determined by increases in bird numbers across years and challenges completed in the Quail Plan but did not result in an observed increase in statewide quail indices. Future quail restoration plans in Kentucky should be directed more toward open production land, which is made up of 6 million acres of pastureland, hay land, row crop agriculture, reverting fields, reclaimed mineland, and grasslands. This work will be completed by utilizing working lands, such as field borders in row crop systems and grazing native warm-season grasses in pasture or hay systems, for wildlife activities. Monitoring systems on these production lands will be in the breeding season only and autonomous recording devices will be

Cattle grazing in CRP grasslands during the nesting season: effects on avian reproduction

AbstractBird populations in grasslands have experienced declines coinciding with loss and fragmentation of prairies. The United States Department of Agriculture (USDA)‐administered Conservation Reserve Program (CRP) is the most extensive grassland restoration program in North America and it has especially benefitted grassland birds. Grazing by domestic cattle has been restricted in CRP during avian nesting seasons despite the potential improvements in structuring habitat for a greater diversity of grassland bird species. Potential negative consequences of grazing in CRP grasslands include trampling of nests by cattle, reductions in nest concealment from predators, and attraction of brood‐parasitic brown‐headed cowbirds (Molothrus ater). We designed an experiment to test for effects of cattle grazing in CRP fields during the nesting season on nest survival and brood parasitism of 5 bird species that commonly nest in CRP grasslands: mourning dove (Zenaida macroura), grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), and eastern (Sturnella magna) and western (S. neglecta) meadowlarks. Grazing was implemented during summers 2017 and 2018 on 17 of 36 fields followed by a year of rest on all fields in 2019. Of the 879 nests on grazed fields, only 4 were likely trampled by cattle (vs. 54% of all nests estimated as failing because of depredation). Experimental grazing (grazed vs. ungrazed fields) had variable effects on nest survival and cowbird parasitism among the bird species analyzed. Negative effects of grazing on daily nest survival of dickcissel and meadowlarks were apparent, at least in some years. We found no direct effects of grazing on nest survival of mourning dove or grasshopper sparrow. Probability and intensity (cowbird offspring/nest) of cowbird parasitism in dickcissel nests was higher on grazed versus ungrazed sites but only in conservation practice (CP) CP2 (vs. CP25 fields). Parasitism probability of grasshopper sparrow nests by cowbirds was higher on grazed fields in the 2 years after introduction of cattle in 2017. Greater vegetative concealment around nest sites was associated with reduced cowbird parasitism of meadowlark and grasshopper sparrow nests and higher nest survival for grasshopper sparrows. Reductions in vegetative height caused by longer‐term or high‐intensity grazing might therefore have negative consequences for some grassland birds by increasing nest site visibility and exposure to cowbird parasitism. Our results indicate that cattle grazing in CRP fields during the nesting season might have some negative effects on reproductive success of some grassland bird species, at least in the short term; however, the potential improvements of structuring habitat to accommodate more grassland bird species and increasing landowner participation in the CRP are considerable.

Plant Community Response and Implications for Wildlife Following Control of a Nonnative Perennial Grass

ABSTRACTRestoration of early successional plant communities dominated by nonnative plant species is a central focus of many state and federal agencies to improve habitat for wildlife associated with these communities. Restoration efforts largely have concentrated on controlling nonnative species followed by planting native grasses and forbs. However, there are numerous establishment problems associated with planting that warrant evaluation of alternative approaches for restoration. We conducted a field experiment to compare vegetation composition and structure as related to habitat for focal wildlife among plant communities established by planting (Planted) native grasses and forbs and revegetation from the seedbank (Seedbank) without planting following control of tall fescue (Schedonorus arundinaceus) at 15 replicated sites in Tennessee and Alabama, USA. Planted and Seedbank treatments produced similar plant communities. Vegetation structure providing cover for nesting and brooding northern bobwhite (Colinus virginianus) and wild turkey (Meleagris gallopavo) was similar between Seedbank and Planted treatments except native grass cover was greatest in Planted, and we recorded greater openness at ground level in Seedbank than Planted or tall fescue control (Control). Abundance of northern bobwhite food plants and selected white‐tailed deer (Odocoileus virginianus) forage were similar between Planted and Seedbank treatments, but nutritional carrying capacity for deer was greatest in Seedbank. Despite similarities in food abundance, and even though all forbs included in the planting mixtures were food plants, the majority of food plants in Planted were from the seedbank. The compositional and structural characteristics deemed most influential in previous studies to selection of breeding sites by dickcissel (Spiza americana), field sparrow (Spizella pusilla), grasshopper sparrow (Ammodramus savannarum), Henslow's sparrow (Ammodramus henslowii), and northern bobwhite were similar in Planted and Seedbank. Tall fescue Control was most similar to characteristics of eastern meadowlark (Sturnella magna) breeding sites. Revegetation following Seedbank produced a plant community that provided habitat for many wildlife species equal to or better than Planted and was 3.7 times less expensive than Planted. © 2021 The Wildlife Society.

Cultural conformity and persistence in Dickcissel song are higher in locations in which males show high site fidelity

Abstract Dickcissel (Spiza americana) males occupying territories in cropland sites produced songs that were less similar on average to other Dickcissel songs in their neighborhood than did Dickcissels living in grasslands, where conformity to the local vocal culture was higher. Further, Dickcissel vocal culture changed more quickly over time in cropland sites relative to grassland sites. These differences may have resulted from the lower site fidelity we observed in Dickcissel males in cropland sites relative to grassland sites. We expected this link with site fidelity because we hypothesized that conformity to local culture in Oscine songbirds and the persistence of culture over time and space are promoted by habitats that facilitate stable populations. In contrast, sites in which habitat features cause rapid population turnover provide more territory vacancies and so more opportunities for colonization. Colonization should drive cultural change, either through adult colonists importing foreign cultural variants or young colonists making errors as they learn the local song. This potential link between population turnover and cultural stability may apply to animal cultures more broadly and so may be a fruitful area for further research. Besides the link between site fidelity and cultural change over time, we also investigated the possibility that habitats with different levels of site fidelity might show differences in the spatial scale of song similarity. However, we found no evidence of such a difference. Finally, although our conclusions regarding conformity and change in vocal culture were based on many recorded songs, automated assessments of song similarity imprecisely estimated the overall degree of song similarity. Thus, we may have underestimated the strength of the effects of time and distance on song similarity.

Effects of prescribed fire timing on vigor of the invasive forb sericea lespedeza (Lespedeza cuneata), total forage biomass accumulation, plant-community composition, and native fauna on tallgrass prairie in the Kansas Flint Hills.

The predominant grazing-management practice of the Kansas Flint Hills involves annual prescribed burning in March or April with postfire grazing by yearling beef cattle at a high stocking density from April to August. There has been a dramatic increase in sericea lespedeza (Lespedeza cuneata [Dumont] G. Don) coincident with this temporally focused use of prescribed fire in the Flint Hills region. The species is an aggressive invader and a statewide noxious weed in Kansas. Control has generally been attempted using repeated herbicide applications. This approach has not limited proliferation of sericea lespedeza and resulted in collateral damage to nontarget flora and fauna. Alternative timing of prescribed fire has not been evaluated for its control. Our objectives for this 4-yr experiment were to (1) document the effects of prescribed burning during early April, early August, or early September on vigor of sericea lespedeza, standing forage biomass, and basal cover of native graminoids, forbs, and shrubs and (2) measure responses to fire regimes by grassland bird and butterfly communities. Whole-plant dry mass, basal cover, and seed production of sericea lespedeza were markedly less (P < 0.01) in areas treated with prescribed fire in August or September compared with April. Forage biomass did not differ (P ≥ 0.43) among treatments when measured during July; moreover, frequencies of bare soil, litter, and total basal plant cover were not different (P ≥ 0.29) among treatments. Combined basal covers of C4 grasses, C3 grasses, annual grasses, forbs, and shrubs also did not differ (P ≥ 0.11) between treatments. Densities of grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), and eastern meadowlark (Sturnella magna) were not negatively affected (P > 0.10) by midsummer or late-summer fires relative to early-spring fires. There were no differences (P > 0.10) in densities of grassland-specialist butterfly species across fire regimes. Under the conditions of our experiment, prescribed burning during summer produced no detrimental effects on forage production, desirable nontarget plant species, grassland birds, or butterfly communities but had strong suppressive effects on sericea lespedeza. Additional research is warranted to investigate how to best incorporate late-summer prescribed fire into common grazing-management practices in the Kansas Flint Hills.

Avian Responses to Vegetation Changes From Post Oak Savanna Restoration Efforts in Eastern Texas

AbstractOnce covering approximately 46 million hectares of the Midwestern United States extending from southern Wisconsin southward into Texas, canopy cover of oak savannas ranged from 10% to 70%, and were dominated by fire-resistant oak species such as bur oak Quercus macrocarpa and post oak Quercus stellata, with a well-developed, diverse herbaceous layer dominated by fire-adapted grasses and forbs. In response to the loss and degradation of oak savannas, associated wildlife populations have experienced long-term declines. For example, 70% of disturbance-dependent bird species in the United States have experienced declines, with most of these species being associated with grasslands, oak savannas, and open forest communities. Few studies have documented the success of restoration in post oak savanna systems in regard to breeding bird assemblages. Our objective was to quantify avian abundance, density, species richness, and assemblage structure under three site conditions (reference, restored, and partially restored [aka unrestored]) within post oak savannas at Gus Engeling Wildlife Management Area in eastern Texas. We conducted vegetation and avian transect surveys postrestoration (2016–2017) and compared our results with prerestoration baseline surveys conducted in 2009. Restoration initiated in 2010 was partially successful, with vegetation changes that closely resemble presettlement characteristics, with the appearance of obligate grassland species. Specifically, prerestoration, one dickcissel Spiza americana and no lark sparrows Chondestes grammacus were detected. By 2017, dickcissel density in the restored sites was similar to densities recorded on tallgrass prairie and other high-quality habitat in the southern portion of its range. Lark sparrows were also detected, but at low densities. We also observed the persistence and increase of several woodland and open woodland species over time. These patterns are likely attributed to the creation of a mosaic of microhabitats selected by these species, such as the persistence of mottes, as well as their increased edge-to-area ratios. Restoration sites that are larger in size and in closer proximity to other restored or remnant savannas should have a higher priority to increase their likelihood of recolonization by target species. Restoration efforts may still be successful in more isolated areas, such as Gus Engeling Wildlife Management Area, but conducting postrestoration monitoring will further elucidate site-specific restoration dynamics.

Not Singing in the Rain: Linking Migratory Songbird Declines With Increasing Precipitation and Brood Parasitism Vulnerability

Few empirical studies have quantified relationships between changing weather and migratory songbirds, but such studies are vital in a time of rapid climate change. Climate change has critical consequences for avian breeding ecology, geographic ranges, and migration phenology. Changing precipitation and temperature patterns affect habitat, food resources, and other aspects of birds’ life history strategies. Such changes may disproportionately affect species confined to rare or declining ecosystems, such as temperate grasslands, which are among the most altered and endangered ecosystems globally. We examined the influence of changing weather on the dickcissel (Spiza americana), a migratory songbird of conservation concern that is an obligate grassland specialist. Our study area in the North American Great Plains features high historic weather variability, where climate change is now driving higher precipitation and temperatures as well as higher frequencies of extreme weather events including flooding and droughts. Dickcissels share their breeding grounds with brown-headed cowbirds (Molothrus ater), brood parasites that lay their eggs in the nests of other songbirds, reducing dickcissel productivity. We used 9 years of capture-recapture data collected over an 18-year period to test the hypothesis that increasing precipitation on dickcissels’ riparian breeding grounds is associated with abundance declines and increasing vulnerability to cowbird parasitism. Dickcissels declined with increasing June precipitation, whereas cowbirds, by contrast, increased. Dickcissel productivity appeared to be extremely low, with a 3:1 ratio of breeding male to female dickcissels likely undermining reproductive success. Our findings suggest that increasing precipitation predicted by climate change models in this region may drive future declines of dickcissels and other songbirds. Drivers of these declines may include habitat and food resource loss related to flooding and higher frequency precipitation events as well as increased parasitism pressure by cowbirds. Positive correlations of June-July precipitation, temperature, and time since grazing with dickcissel productivity did not mitigate dickcissels’ declining trend in this ecosystem. These findings highlight the importance of empirical research on the effects of increasing precipitation and brood parasitism vulnerability on migratory songbird conservation to inform adaptive management under climate change.

Does Conservation Practice and Site Age Influence Vegetation Structure and Avian Abundance in Restored Fields?

ABSTRACTFarmland set‐aside programs provide important habitat for many wildlife species, yet little information exists regarding how vegetation structure and species respond to conservation practice and site age. This information could provide managers with a guide for how to implement, enhance, and maintain wildlife benefits of conservation programs. We describe how vegetation structure and avian species respond to conservation practice and time since restoration at 172 sites enrolled in the Conservation Reserve Enhancement Program (CREP) in Illinois, USA. We surveyed 172 sites enrolled in 4 different conservation practices (CP) within CREP during the breeding seasons of 2012–2015 using avian point counts and vegetation surveys. Vegetation structure and composition varied among CPs, with hardwood tree plantings (CP3A) having the greatest amount of understory vegetation and tree cover. Conversely, permanent wildlife habitat (CP4D) had the greatest grass cover and least tree cover. Many bird species were found in similar numbers across CP types; however, only dickcissel (Spiza americana) density was greater in sites enrolled as permanent wildlife habitat. Bell's vireo (Vireo bellii) and yellow‐billed cuckoo (Coccyzus americanus) were more numerous in hardwood tree plantings. Dickcissel density decreased and field sparrow (Spizella pusilla) density increased as fields aged, but the relationships were not consistent among CP types. Differences among CPs largely resulted from differences in dominance in woody vegetation due to initial habitat management and differential succession rates. Interestingly, many of our focal species had wider successional tolerances than previously suggested. Overall, our results demonstrate that conservation benefits change over time depending on the starting CP, that there can be considerable similarity in vegetation structure and bird communities among what appear to be very different conservation practices. This information can be used to target conservation benefits toward conservation priority species. © 2020 The Wildlife Society.

Do habitat preferences improve fitness? Context-specific adaptive habitat selection by a grassland songbird.

Animals are predicted to prefer high-quality over low-quality habitats, but adaptive habitat selection is less straightforward than often assumed. Preferences may improve only specific fitness metrics at particular spatial scales, with variation across time or between sexes. Preferences sometimes even reduce fitness. We investigated the context specificity of adaptive habitat selection, studying dickcissels (Spiza americana)-a polygynous songbird-as a model. From 2014 to 2015, we measured male and female habitat preferences at two scales (territories and landscape patches) on 21 grassland patches in Ringgold County, Iowa, USA. We tested whether preferences improved four fitness metrics-polygyny, avoidance of brood parasitism by brown-headed cowbirds (Molothrus ater), fledgling productivity, and offspring condition. Both sexes preferred territories where offspring attained superior condition and patches where parasitism was infrequent. Females preferred patches where nests produced more fledglings, and in 2014, males on preferred (i.e., early-established) territories attracted more mates and produced more fledglings. However, males on non-preferred (i.e., late-established) territories were more successful in 2015. This inconsistency may have arisen because females were abundant and nest-predation rates were low in May-June 2014, allowing early-settling males to produce many young. In 2015, however, females were more abundant and nests more successful later in the breeding season. Our results show that habitat preferences do not uniformly improve fitness, and some benefits differ between sexes. Moreover, preference-fitness relationships only manifest at specific scales, and annual variation in population and predation dynamics can limit consistency. Detecting adaptive habitat selection thus requires multi-year measurements and careful consideration of relevant scales.

Pasture-scale vegetation predicts Dickcissel nest-site selection and success in native and exotic grass pastures

AbstractExotic grasses such as bermudagrass (Cynodon dactylon) and tall fescue (Schedonorus arundinaceus) are widely established across the southeastern United States as livestock forage, but their structure and management can limit avian reproductive success. Native warm-season grasses (NWSG) are promoted as sustainable forage alternatives. To examine nesting suitability for tall structure specialists such as Dickcissels (Spiza americana) we established an operational-scale study in northeastern Mississippi, USA, with 4 treatments along a gradient of beef production intensity. Treatments included grazed exotic forages, 2 grazed NWSG treatments including Indiangrass (Sorghastrum nutans) monoculture and NWSG polyculture of Indiangrass, little bluestem (Schizachyrium scoparium), and big bluestem (Andropogon gerardii), and an ungrazed NWSG polyculture treatment. We monitored 208 Dickcissel nests in 2011 and 2012 to evaluate effects of treatment, vegetation structure, fire ants (Solenopsis spp.), and arthropod prey biomass on nest-site selection and nest survival. Survival rates varied among treatments and increased with pasture-scale visual obstruction reading (VOR), being lowest among grazed exotic grass, intermediate in grazed NWSG, and highest in ungrazed NWSG. Although Dickcissels selected nest sites with greater VOR, we found little support for effects of nest-site vegetation on survival. However, nest survival was lower for nests in shrubs that also occurred in pastures with greater shrub cover, and selection for shrubs declined as pasture-scale VOR increased, suggesting a functional response in selection. We found little support for food availability influencing nest survival. These results suggest NWSG pastures increase Dickcissel nest success through greater pasture-scale VOR by reducing Dickcissel selection of shrubs for nest sites, and possibly by reducing predator efficiency. Incorporating NWSG into beef production systems while maintaining availability of tall vegetation could benefit Dickcissels and other tall structure specialists.

Species-specific and temporal scale-dependent responses of birds to drought.

Global climate change is increasing the frequency and intensity of weather extremes, including severe droughts in many regions. Drought can impact organisms by inhibiting reproduction, reducing survival and abundance, and forcing range shifts. For birds, considering temporal scale by averaging drought-related variables over different time lengths (i.e., temporal grains) captures different hydrologic attributes which may uniquely influence food supplies, vegetation greenness/structure, and other factors affecting populations. However, studies examining drought impacts on birds often assess a single temporal grain without considering that different species have different life histories that likely determine the temporal grain of their drought response. Furthermore, while drought is known to influence bird abundance and drive between-year range shifts, less understood is whether it causes within-range changes in species distributions. Our objectives were to (a) determine which temporal grain of drought (if any) is most related to bird presence/absence and whether this response is species specific; and (b) assess whether drought alters bird distributions by quantifying probability of local colonization and extinction as a function of drought intensity. We used North American Breeding Bird Survey data collected over 16years, generalized linear mixed models, and dynamic occupancy models to meet these objectives. Different bird species responded to drought at different temporal grains, with most showing the strongest signal at annual or near-annual grains. For all drought-responsive species, increased drought intensity at any temporal grain always correlated with decreased occupancy. Additionally, colonization/extinction analyses indicated that one species, the dickcissel (Spiza americana), is more likely to colonize novel areas within the southern/core portion of its range during drought. Considering drought at different temporal grains, along with hydrologic attributes captured by each grain, may better reveal mechanisms behind drought impacts on birds and other organisms, and therefore improve understanding of how global climate change impacts species and the landscapes they inhabit.