Grassland Bird Responses to Land Management in the Largest Remaining Tallgrass Prairie

Abstract: Extensive habitat loss and changing agricultural practices have caused widespread declines in grassland birds throughout North America. The Flint Hills of Kansas and Oklahoma—the largest remaining tallgrass prairie—is important for grassland bird conservation despite supporting a major cattle industry. In 2004 and 2005, we assessed the community, population, and demographic responses of grassland birds to the predominant management practices (grazing, burning, and haying) of the region, including grasslands restored under the Conservation Reserve Program (CRP). We targeted 3 species at the core of this avian community: the Dickcissel (Spiza americana), Grasshopper Sparrow (Ammodramus savannarum), and Eastern Meadowlark (Sturnella magna). Bird diversity was higher in native prairie hayfields and grazed pastures than CRP fields, which were dominated by Dickcissels. Although Dickcissel density was highest in CRP, their nest success was highest and nest parasitism by Brown‐headed Cowbirds (Moluthrus ater) lowest in unburned hayfields (in 2004). Conversely, Grasshopper Sparrow density was highest in grazed pastures, but their nest success was lowest in these pastures and highest in burned hayfields, where cowbird parasitism was also lowest (in 2004). Management did not influence density and nest survival of Eastern Meadowlarks, which were uniformly low across the region. Nest success was extremely low (5–12%) for all 3 species in 2005, perhaps because of a record spring drought. Although the CRP has benefited grassland birds in agricultural landscapes, these areas may have lower habitat value in the context of native prairie. Hayfields may provide beneficial habitat for some grassland birds in the Flint Hills because they are mowed later in the breeding season than elsewhere in the Midwest. Widespread grazing and annual burning have homogenized habitat—and thus grassland‐bird responses—across the Flint Hills. Diversification of management practices could increase habitat heterogeneity and enhance the conservation potential of the Flint Hills for grassland birds.     

A counterfactual approach to measure the impact of wet grassland conservation on U.K. breeding bird populations

Wet grassland populations of wading birds in the United Kingdom have declined severely since 1990. To help mitigate these declines, the Royal Society for the Protection of Birds has restored and managed lowland wet grassland nature reserves to benefit these and other species. However, the impact of these reserves on bird population trends has not been evaluated experimentally due to a lack of control populations. We compared population trends from 1994 to 2018 among 5 bird species of conservation concern that breed on these nature reserves with counterfactual trends created from matched breeding bird survey observations. We compared reserve trends with 3 different counterfactuals based on different scenarios of how reserve populations could have developed in the absence of conservation. Effects of conservation interventions were positive for all 4 targeted wading bird species: Lapwing (Vanellus vanellus), Redshank (Tringa totanus), Curlew (Numenius arquata), and Snipe (Gallinago gallinago). There was no positive effect of conservation interventions on reserves for the passerine, Yellow Wagtail (Motacilla flava). Our approach using monitoring data to produce valid counterfactual controls is a broadly applicable method allowing large-scale evaluation of conservation impact.     

Optimizing conservation in species-specific agricultural landscapes

Recovery of grassland birds in agricultural landscapes is a global imperative. Agricultural landscapes are complex, and the value of resource patches may vary substantially among species. The spatial extent at which landscape features affect populations (i.e., scale of effect) may also differ among species. There is a need for regional-scale conservation planning that considers landscape-scale and species-specific responses of grassland birds to environmental change. We developed a spatially explicit approach to optimizing grassland conservation in the context of species-specific landscapes and prioritization of species recovery and applied it to a conservation program in Kentucky (USA). We used a hierarchical distance-sampling model with an embedded scale of effect predictor to estimate the relationship between landscape structure and abundance of eastern meadowlarks (Sturnella magna), field sparrows (Spizella pusilla), and northern bobwhites (Colinus virginianus). We used a novel spatially explicit optimization procedure rooted in multi-attribute utility theory to design alternative conservation strategies (e.g., prioritize only northern bobwhite recovery or assign equal weight to each species’ recovery). Eastern meadowlarks and field sparrows were more likely to respond to landscape-scale resource patch adjacencies than landscape-scale patch densities. Northern bobwhite responded to both landscape-scale resource patch adjacencies and densities and responded strongly to increased grassland density. Effects of landscape features on local abundance decreased as distance increased and had negligible influence at 0.8 km for eastern meadowlarks (0.7–1.2 km 95% Bayesian credibility intervals [BCI]), 2.5 km for field sparrows (1.5–5.8 km 95% BCI), and 8.4 km for bobwhite (6.4–26 km 95% BCI). Northern bobwhites were predicted to benefit greatly from future grassland conservation regardless of conservation priorities, but eastern meadowlark and field sparrow were not. Our results suggest similar species can respond differently to broad-scale conservation practices because of species-specific, distance-dependent relationships with landscape structure. Our framework is quantitative, conceptually simple, customizable, and predictive and can be used to optimize conservation in heterogeneous ecosystems while considering landscape-scale processes and explicit prioritization of species recovery.     

A Comparison of Landscapes Occupied by Increasing and Decreasing Populations of Grassland Birds

Abstract:  For several decades, many grassland bird species have been declining in abundance throughout the Midwest and Great Plains regions of the United States, possibly due to loss of natural grassland habitat and increasing urbanization. I used 20 years of data from the North American Breeding Bird Survey to identify increasing, decreasing, and stable populations of 36 grassland-nesting bird species. I characterized the immediate landscape (circle with radius = 30 km) surrounding each population based on data from the National Resources Inventory. For each landscape, I calculated the proportion of eight different land-cover types: restored grassland, rangeland, cultivated cropland, pasture, noncultivated cropland, forest, urban land, and water. Using a null model, I compared landscape composition of increasing, decreasing, and stable populations. As predicted on the basis of the habitat preferences of grassland birds, increasing populations inhabited landscapes that contained significantly more restored grassland and rangeland but significantly less forest land and urban land than landscapes inhabited by decreasing populations. There was no significant difference in the proportion of cropland within the landscapes of increasing and decreasing populations, although cropland composed a large proportion (>30%) of many landscapes. In contrast, restored grassland typically composed a very small proportion (<3.5%) of total land cover, yet it was significantly more common in the landscapes of increasing than decreasing populations. These results suggest that grassland birds may benefit from government initiatives, such as the Conservation Reserve Program, that promote the restoration of grassland at a landscape scale.     

Building a better baseline to estimate 160 years of avian population change and create historically informed conservation targets

Globally, anthropogenic land-cover change has been dramatic over the last few centuries and is frequently invoked as a major cause of wildlife population declines. Baseline data currently used to assess population trends, however, began well after major changes to the landscape. In the United States and Canada, breeding bird population trends are assessed by the North American Breeding Bird Survey, which began in the 1960s. Estimates of distribution and abundance prior to major habitat alteration would add historical perspective to contemporary trends and allow for historically based conservation targets. We used a hindcasting framework to estimate change in distribution and abundance of 7 bird species in the Willamette Valley, Oregon (United States). After reconciling classification schemes of current and 1850s reconstructed land cover, we used multiscale species distribution models and hierarchical distance sampling models to predict spatially explicit densities in the modern and historical landscapes. We estimated that since the 1850s, White-breasted Nuthatch (Sitta carolinensis) and Western Meadowlark (Sturnella neglecta) populations, 2 species sensitive to fragmentation of oak woodlands and grasslands, declined by 93% and 97%, respectively. Five other species we estimated nearly stable or increasing populations, despite steep regional declines since the 1960s. Based on these estimates, we developed historically based conservation targets for amount of habitat, population, and density for each species. Hindcasted reconstructions provide historical perspective for assessing contemporary trends and allow for historically based conservation targets that can inform current management.     

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. Evaluación de los Beneficios de la Mutliregionalidad de Aves a Partir de Amortiguadores Agriculturales Estratégicamente Señalados     

Long-term declines of European insectivorous bird populations and potential causes

Evidence of declines in insect populations has recently received considerable scientific and societal attention. However, the lack of long-term insect monitoring makes it difficult to assess whether declines are geographically widespread. By contrast, bird populations are well monitored and often used as indicators of environmental change. We compared the population trends of European insectivorous birds with those of other birds to assess whether patterns in bird population trends were consistent with declines of insects. We further examined whether declines were evident for insectivores with different habitats, foraging strata, and other ecological preferences. Bird population trends were estimated for Europe (1990–2015) and Denmark (1990–2016). On average, insectivores declined over the study period (13% across Europe and 28% in Denmark), whereas omnivores had stable populations. Seedeaters also declined (28% across Europe; 34% in Denmark), but this assessment was based on fewer species than for other groups. The effects of insectivory were stronger for farmland species (especially grassland species), for ground feeders, and for cold-adapted species. Insectivory was associated with long-distance migration, which was also linked to population declines. However, many insectivores had stable populations, especially habitat generalists. Our findings suggest that the decline of insectivores is primarily associated with agricultural intensification and loss of grassland habitat. The loss of both seed and insect specialists indicates an overall trend toward bird communities dominated by diet generalists.     

Assessing strategies to reconcile agriculture and bird conservation in the temperate grasslands of South America

Globally, agriculture is the greatest source of threat to biodiversity, through both ongoing conversion of natural habitat and intensification of existing farmland. Land sparing and land sharing have been suggested as alternative approaches to reconcile this threat with the need for land to produce food. To examine which approach holds most promise for grassland species, we examined how bird population densities changed with farm yield (production per unit area) in the Campos of Brazil and Uruguay. We obtained information on biodiversity and crop yields from 24 sites that differed in agricultural yield. Density–yield functions were fitted for 121 bird species to describe the response of population densities to increasing farm yield, measured in terms of both food energy and profit. We categorized individual species according to how their population changed across the yield gradient as being positively or negatively affected by farming and according to whether the species’ total population size was greater under land‐sparing, land‐sharing, or an intermediate strategy. Irrespective of the yield, most species were negatively affected by farming. Increasing yields reduced densities of approximately 80% of bird species. We estimated land sparing would result in larger populations than other sorts of strategies for 67% to 70% of negatively affected species, given current production levels, including three threatened species. This suggests that increasing yields in some areas while reducing grazing to low levels elsewhere may be the best option for bird conservation in these grasslands. Implementing such an approach would require conservation and production policies to be explicitly linked to support yield increases in farmed areas and concurrently guarantee that larger areas of lightly grazed natural grasslands are set aside for conservation.     

Application of multiple-population viability analysis to evaluate species recovery alternatives

Population viability analysis (PVA) is a powerful conservation tool, but it remains impractical for many species, particularly species with multiple, broadly distributed populations for which collecting suitable data can be challenging. A recently developed method of multiple-population viability analysis (MPVA), however, addresses many limitations of traditional PVA. We built on previous development of MPVA for Lahontan cutthroat trout (LCT) (Oncorhynchus clarkii henshawi), a species listed under the U.S. Endangered Species Act, that is distributed broadly across habitat fragments in the Great Basin (U.S.A.). We simulated potential management scenarios and assessed their effects on population sizes and extinction risks in 211 streams, where LCT exist or may be reintroduced. Conservation populations (those managed for recovery) tended to have lower extinction risks than nonconservation populations (mean = 19.8% vs. 52.7%), but not always. Active management or reprioritization may be warranted in some cases. Eliminating non-native trout had a strong positive effect on overall carrying capacities for LCT populations but often did not translate into lower extinction risks unless simulations also reduced associated stochasticity (to the mean for populations without non-native trout). Sixty fish or 5–10 fish/km was the minimum reintroduction number and density, respectively, that provided near-maximum reintroduction success. This modeling framework provided crucial insights and empirical justification for conservation planning and specific adaptive management actions for this threatened species. More broadly, MPVA is applicable to a wide range of species exhibiting geographic rarity and limited availability of abundance data and greatly extends the potential use of empirical PVA for conservation assessment and planning.     

Determinants of bird conservation‐action implementation and associated population trends of threatened species

Conservation actions, such as habitat protection, attempt to halt the loss of threatened species and help their populations recover. The efficiency and the effectiveness of actions have been examined individually. However, conservation actions generally occur simultaneously, so the full suite of implemented conservation actions should be assessed. We used the conservation actions underway for all threatened and near‐threatened birds of the world (International Union for Conservation of Nature Red List of Threatened Species) to assess which biological (related to taxonomy and ecology) and anthropogenic (related to geoeconomics) factors were associated with the implementation of different classes of conservation actions. We also assessed which conservation actions were associated with population increases in the species targeted. Extinction‐risk category was the strongest single predictor of the type of conservation actions implemented, followed by landmass type (continent, oceanic island, etc.) and generation length. Species targeted by invasive nonnative species control or eradication programs, ex situ conservation, international legislation, reintroduction, or education, and awareness‐raising activities were more likely to have increasing populations. These results illustrate the importance of developing a predictive science of conservation actions and the relative benefits of each class of implemented conservation action for threatened and near‐threatened birds worldwide.     

Validating graph-based connectivity models with independent presence–absence and genetic data sets

Habitat connectivity is a key objective of current conservation policies and is commonly modeled by landscape graphs (i.e., sets of habitat patches [nodes] connected by potential dispersal paths [links]). These graphs are often built based on expert opinion or species distribution models (SDMs) and therefore lack empirical validation from data more closely reflecting functional connectivity. Accordingly, we tested whether landscape graphs reflect how habitat connectivity influences gene flow, which is one of the main ecoevolutionary processes. To that purpose, we modeled the habitat network of a forest bird (plumbeous warbler [Setophaga plumbea]) on Guadeloupe with graphs based on expert opinion, Jacobs’ specialization indices, and an SDM. We used genetic data (712 birds from 27 populations) to compute local genetic indices and pairwise genetic distances. Finally, we assessed the relationships between genetic distances or indices and cost distances or connectivity metrics with maximum-likelihood population-effects distance models and Spearman correlations between metrics. Overall, the landscape graphs reliably reflected the influence of connectivity on population genetic structure; validation R² was up to 0.30 and correlation coefficients were up to 0.71. Yet, the relationship among graph ecological relevance, data requirements, and construction and analysis methods was not straightforward because the graph based on the most complex construction method (species distribution modeling) sometimes had less ecological relevance than the others. Cross-validation methods and sensitivity analyzes allowed us to make the advantages and limitations of each construction method spatially explicit. We confirmed the relevance of landscape graphs for conservation modeling but recommend a case-specific consideration of the cost-effectiveness of their construction methods. We hope the replication of independent validation approaches across species and landscapes will strengthen the ecological relevance of connectivity models.     

A global ecological signal of extinction risk in terrestrial vertebrates

To determine the distribution and causes of extinction threat across functional groups of terrestrial vertebrates, we assembled an ecological trait data set for 18,016 species of terrestrial vertebrates and utilized phylogenetic comparative methods to test which categories of habitat association, mode of locomotion, and feeding mode best predicted extinction risk. We also examined the individual categories of the International Union for Conservation of Nature Red List extinction drivers (e.g., agriculture and logging) threatening each species and determined the greatest threats for each of the four terrestrial vertebrate groups. We then quantified the sum of extinction drivers threatening each species to provide a multistressor perspective on threat. Cave dwelling amphibians (p < 0.01), arboreal quadrupedal mammals (all of which are primates) (p < 0.01), aerial and scavenging birds (p < 0.01), and pedal (i.e., walking) squamates (p < 0.01) were all disproportionately threatened with extinction in comparison with the other assessed ecological traits. Across all threatened vertebrate species in the study, the most common risk factors were agriculture, threatening 4491 species, followed by logging, threatening 3187 species, and then invasive species and disease, threatening 2053 species. Species at higher risk of extinction were simultaneously at risk from a greater number of threat types. If left unabated, the disproportionate loss of species with certain functional traits and increasing anthropogenic pressures are likely to disrupt ecosystem functions globally. A shift in focus from species- to trait-centric conservation practices will allow for protection of at-risk functional diversity from regional to global scales.     

Bridging gaps in demographic analysis with phylogenetic imputation

Phylogenetically informed imputation methods have rarely been applied to estimate missing values in demographic data but may be a powerful tool for reconstructing vital rates of survival, maturation, and fecundity for species of conservation concern. Imputed vital rates could be used to parameterize demographic models to explore how populations respond when vital rates are perturbed. We used standardized vital rate estimates for 50 bird species to assess the use of phylogenetic imputation to fill gaps in demographic data. We calculated imputation accuracy for vital rates of focal species excluded from the data set either singly or in combination and with and without phylogeny, body mass, and life-history trait data. We used imputed vital rates to calculate demographic metrics, including generation time, to validate the use of imputation in demographic analyses. Covariance among vital rates and other trait data provided a strong basis to guide imputation of missing vital rates in birds, even in the absence of phylogenetic information. Mean NRMSE for null and phylogenetic models differed by <0.01 except when no vital rates were available or for vital rates with high phylogenetic signal (Pagel's λ > 0.8). In these cases, including body mass and life-history trait data compensated for lack of phylogenetic information: mean normalized root mean square error (NRMSE) for null and phylogenetic models differed by <0.01 for adult survival and <0.04 for maturation rate. Estimates of demographic metrics were sensitive to the accuracy of imputed vital rates. For example, mean error in generation time doubled in response to inaccurate estimates of maturation time. Accurate demographic data and metrics, such as generation time, are needed to inform conservation planning processes, for example through International Union for Conservation of Nature Red List assessments and population viability analysis. Imputed vital rates could be useful in this context but, as for any estimated model parameters, awareness of the sensitivities of demographic model outputs to the imputed vital rates is essential.     

Effectiveness of Predator Removal for Enhancing Bird Populations

Abstract: Predation pressure on vulnerable bird species has made predator control an important issue for international nature conservation. Predator removal by culling or translocation is controversial, expensive, and time‐consuming, and results are often temporary. Thus, it is important to assess its effectiveness from all available evidence. We used explicit systematic review methodology to determine the impact of predator removal on four measurable responses in birds: breeding performance (hatching success and fledging success) and population size (breeding and postbreeding). We used meta‐analysis to summarize results from 83 predator removal studies from six continents. We also investigated whether characteristics of the prey, predator species, location, and study methodology explained heterogeneity in effect sizes. Removing predators increased hatching success, fledging success, and breeding populations. Removing all predator species achieved a significantly larger increase in breeding population than removing only a subset. Postbreeding population size was not improved on islands, or overall, but did increase on mainlands. Heterogeneity in effect sizes for the four population parameters was not explained by whether predators were native or introduced; prey were declining, migratory, or game species; or by the study methodology. Effect sizes for fledging success were smaller for ground‐nesting birds than those that nest elsewhere, but the difference was not significant. We conclude that current evidence indicates that predator removal is an effective strategy for the conservation of vulnerable bird populations. Nevertheless, the ethical and practical problems associated with predator removal may lead managers to favor alternative, nonlethal solutions. Research is needed to provide and synthesize data to determine whether these are effective management practices for future policies on bird conservation.     

Modelling trade-offs between livestock grazing and wader conservation in a grassland agroecosystem

The objective of this study was to model the trade-offs between ecological and productive performance of a grassland agroecosystem. We developed a dynamic model linking grass dynamics controlled by livestock grazing to stochastic population dynamics of two wader bird species with high conservation value. Bird dynamics were driven by both direct and indirect effects of grazing. Viable control framework was used to predict grazing strategies ensuring production and conservation and to generate the whole trade-off curve between ecological and productive performance. Bird population size was used as an indicator of ecological performance and the total number of grazing days defined productive performance. Model results show that conciliating ecological and productive performance implies a temporal shift in grazing sequences. The best ecological performance was obtained at intermediate levels of productive performance. Without grazing or with too low a grazing intensity, it was not possible to maintain any of the bird populations due to the indirect effects of grazing on habitat quality. However, too high a level of grazing implied fast population decline for both populations due to direct negative effects of grazing on nest survival. Field data on current grazing regimes and grass height showed a low proportion of suitable fields in our case study area. This result indicates an antagonism between direct and indirect effects of grazing on wader birds, implying the need of very specific management of grassland. Our results illustrate the fact that European grasslands are anthropic habitats which are highly dependent on human activity. In such habitats, trade-off curves are not expected to be strictly decreasing or increasing.     

Population Bottlenecks and Increased Hatching Failure in Endangered Birds

Abstract: Severe population bottlenecks are expected to lead to increases in inbreeding depression and to reduce the long‐term viability of populations. We compared hatching failure across 51 threatened bird species to test the relation between the size of population bottleneck and population viability. Bottleneck size was defined as the lowest population size recorded in a species. Hatching failure was estimated as the proportion of eggs that failed to hatch due to infertility and embryonic death, both of which increase with inbreeding. The size of the bottleneck varied from 4 to 20,000 individuals across species and had a significant negative effect on hatching failure, a pattern that was consistent when we controlled for the confounding effects of phylogeny, body size, clutch size, time since the bottleneck occurred, and latitude. Hatching failure varied from 3 to 64% across species and was more than 10% in all populations passing through bottlenecks below 100–150 individuals. Our results show that the negative consequences of bottlenecks on hatching success are widespread in the populations of species we examined, and emphasize the conservation benefit of preventing bottlenecks below 150 individuals.     

Effects of temperature and precipitation on grassland bird nesting success as mediated by patch size

Grassland birds are declining faster than any other bird guild across North America. Shrinking ranges and population declines are attributed to widespread habitat loss and increasingly fragmented landscapes of agriculture and other land uses that are misaligned with grassland bird conservation. Concurrent with habitat loss and degradation, temperate grasslands have been disproportionally affected by climate change relative to most other terrestrial biomes. Distributions of grassland birds often correlate with gradients in climate, but few researchers have explored the consequences of weather on the demography of grassland birds inhabiting a range of grassland fragments. To do so, we modeled the effects of temperature and precipitation on nesting success rates of 12 grassland bird species inhabiting a range of grassland patches across North America (21,000 nests from 81 individual studies). Higher amounts of precipitation in the preceding year were associated with higher nesting success, but wetter conditions during the active breeding season reduced nesting success. Extremely cold or hot conditions during the early breeding season were associated with lower rates of nesting success. The direct and indirect influence of temperature and precipitation on nesting success was moderated by grassland patch size. The positive effects of precipitation in the preceding year on nesting success were strongest in relatively small grassland patches and had little effect in large patches. Conversely, warm temperatures reduced nesting success in small grassland patches but increased nesting success in large patches. Mechanisms underlying these differences may be patch‐size‐induced variation in microclimates and predator activity. Although the exact cause is unclear, large grassland patches, the most common metric of grassland conservation, appears to moderate the effects of weather on grassland‐bird demography and could be an effective component of climate‐change adaptation.     

Bird conservation and the land sharing-sparing continuum in farmland-dominated landscapes of lowland England

Empirical evidence from many regions suggests that most species would be least negatively affected if human food demand were met through high-yield agricultural production and conservation of nonfarm ecosystems (land sparing), rather than through wildlife-friendly farming over a larger area (land sharing). However, repeated glaciation and a long history of agriculture may lead to different results in regions such as western Europe. We compared the consequences of land sparing and land sharing on breeding bird species in 2 lowland regions of England, The Fens, with 101 species, and Salisbury Plain, with 83. We derived density–yield responses for each species and then estimated regional population size under regional food production strategies, including land sharing and land sparing, a range of intermediate strategies, and a novel mixed strategy. In both regions, more species achieved maximum regional population size under land sparing than land sharing. In The Fens, the majority of birds were loser species (estimated to have smaller populations under all food production strategies than in the preagricultural baseline scenario), whereas in Salisbury Plain the majority were winners (smaller populations in the preagricultural baseline scenario). Loser species overwhelmingly achieved maximum regional population size under land sparing, whereas winner species achieved maximum regional population size under either land sharing or an intermediate strategy, highlighting the importance of defining which groups of species are the target of conservation. A novel 3-compartment strategy (combining high-yield farming, natural habitat, and low-yield farming) often performed better than either land sharing or land sparing. Our results support intermediate or 3-compartment land-sparing strategies to maximize bird populations across lowland agricultural landscapes. To deliver conservation outcomes, any shift toward land sparing must, however, ensure yield increases are sustainable in the long term, do not entail increased negative effects on surrounding areas, and are linked to allocation of land for nature.     

Optimal Management of a Multispecies Shorebird Flyway under Sea‐Level Rise

Every year, millions of migratory shorebirds fly through the East Asian–Australasian Flyway between their arctic breeding grounds and Australasia. This flyway includes numerous coastal wetlands in Asia and the Pacific that are used as stopover sites where birds rest and feed. Loss of a few important stopover sites through sea‐level rise (SLR) could cause sudden population declines. We formulated and solved mathematically the problem of how to identify the most important stopover sites to minimize losses of bird populations across flyways by conserving land that facilitates upshore shifts of tidal flats in response to SLR. To guide conservation investment that minimizes losses of migratory bird populations during migration, we developed a spatially explicit flyway model coupled with a maximum flow algorithm. Migratory routes of 10 shorebird taxa were modeled in a graph theoretic framework by representing clusters of important wetlands as nodes and the number of birds flying between 2 nodes as edges. We also evaluated several resource allocation algorithms that required only partial information on flyway connectivity (node strategy, based on the impacts of SLR at nodes; habitat strategy, based on habitat change at sites; population strategy, based on population change at sites; and random investment). The resource allocation algorithms based on flyway information performed on average 15% better than simpler allocations based on patterns of habitat loss or local bird counts. The Yellow Sea region stood out as the most important priority for effective conservation of migratory shorebirds, but investment in this area alone will not ensure the persistence of species across the flyway. The spatial distribution of conservation investments differed enormously according to the severity of SLR and whether information about flyway connectivity was used to guide the prioritizations. With the rapid ongoing loss of coastal wetlands globally, our method provides insight into efficient conservation planning for migratory species. Gestión Óptima de una Ruta Migratoria de Múltiples Especies de Aves Costeras Sometida a Incremento del Nivel del Mar