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Halting the global decline of migratory birds requires a better understanding of migration ecology. Stopover sites are a crucial yet understudied aspect of bird conservation, mostly due to challenges associated with understanding broad-scale patterns of transient habitat use. Here, we use a national network of weather radar stations to identify stopover hotspots and assess multiscale habitat associations of migratory landbirds across the eastern United States during autumn migration. We mapped seasonal bird densities over 5 y (2015 to 2019) from 60 radar stations covering 63.2 million hectares. At a coarse scale, we found that landbirds migrate across a broad front with small differences in migrant density between radar domains. However, relatively more birds concentrate along the Mississippi River and Appalachian Mountains. At a finer scale, we identified radar pixels that consistently harbored high densities of migrants for all 5 y, which we classify as stopover hotspots. Hotspot probability increased with percent cover of all forest types and decreased with percent cover of pasture and cultivated crops. Moreover, we found strong concentrating effects of deciduous forest patches within deforested regions. We also found that the prairie biome in the Midwest (now mostly cropland) is likely a migration barrier, with large concentrations of migrants at the prairie--forest boundary after crossing the agricultural Midwest. Overall, the broad-front migration pattern highlights the importance of locally based conservation efforts to protect stopover habitats. Such efforts should target forests, especially deciduous forests in highly altered landscapes. These findings demonstrate the value of multiscale habitat assessments for the conservation of migratory landbirds. [ABSTRACT FROM AUTHOR]

As wind energy rapidly expands worldwide, information to minimize impacts of this development on biodiversity is urgently needed. Here we demonstrate how data collected by weather radar networks can inform placement and operation of wind facilities to reduce collisions and minimize habitat‐related impacts on nocturnally migrating birds. We found over a third of nocturnal migrants flew through altitudes within the rotor‐swept zone surrounding the North American Great Lakes, a continentally important migration corridor. Migrating birds concentrated in terrestrial stopover habitats within 20‐km from shorelines, a distance well beyond the current guidelines for construction of new land‐based facilities, and their distributions varied seasonally and at local and regional scales, creating predictable opportunities to minimize impacts from wind energy development and operation. Networked radar data are available across the United States and other countries and broad application of this approach could provide information critical to bird‐friendly expansion of this globally important energy source. [ABSTRACT FROM AUTHOR]

Operational weather surveillance radars (WSRs) are permanent radars that constantly detect precipitation at regular intervals (approx. every 4–10 min) for the purpose of weather reporting and are often part of a larger network of radars. Ecological studies using WSR to detect flying animals within the airspace have been on the rise since the early 2000s. However, the vast majority of published ecological studies (>300) have occurred in the Northern Hemisphere with only two published studies occurring in the Southern Hemisphere, both on insects. The lag in uptake of the technique in the Southern hemisphere is likely due to limited WSR coverage and the challenges of data acquisition and interpretation. However, we argue that WSRs are numerous enough in the Southern Hemisphere to offer equal opportunity to understand the movement of flying animals there. Here, we explore why that might be and present a road map so that ecological researchers in the Southern Hemisphere may take advantage of this valuable data resource. [ABSTRACT FROM AUTHOR]

Urban environments impose novel selection pressures with varying impacts across species and life history stages. The post‐fledging stage for migratory passerines, defined as the period of time from when hatch‐year birds fledge until their first migration, is a poorly understood component of annual productivity that potentially limits population growth. We studied two migratory passerines with positive and negative population responses to urbanization, respectively: gray catbird Dumetella carolinensis and wood thrush Hylocichla mustelina. Our goals were to estimate post‐fledging survival rates for urban bird populations and determine which features of the urban landscape impact mortality risk during the post‐fledging stage. From 2012–2014, we tracked 127 fledglings (60 gray catbirds and 67 wood thrushes). Over 55 d after fledging, cumulative survival of gray catbirds (0.32 [95% CI: 0.22–0.47]) was approximately half that of wood thrushes (0.63 [95% CI: 0.52–0.75]). Thus, survival rates during the post‐fledging stage, taken in isolation, do not explain differential trajectories of gray catbird and wood thrush populations in urban environments. Most mortality (86%) for both species was due to predation. However, after reaching independence from parental care, 6 birds (9.4% of mortalities) died of anthropogenic causes (e.g. building, car strikes). Crossing roads significantly increased mortality risk, but increasing daily movement distance decreased mortality risk. Our results raise the question of whether anthropogenic sources of mortality are compensatory or additive to natural mortality; we emphasize the need to monitor fledgling survival beyond the parental‐dependence stage in order to fully understand the impacts of anthropogenic hazards on juvenile birds. [ABSTRACT FROM AUTHOR]

Abstract: With many of the world's migratory bird populations in alarming decline, broad‐scale assessments of responses to migratory hazards may prove crucial to successful conservation efforts. Most birds migrate at night through increasingly light‐polluted skies. Bright light sources can attract airborne migrants and lead to collisions with structures, but might also influence selection of migratory stopover habitat and thereby acquisition of food resources. We demonstrate, using multi‐year weather radar measurements of nocturnal migrants across the northeastern U.S., that autumnal migrant stopover density increased at regional scales with proximity to the brightest areas, but decreased within a few kilometers of brightly‐lit sources. This finding implies broad‐scale attraction to artificial light while airborne, impeding selection for extensive forest habitat. Given that high‐quality stopover habitat is critical to successful migration, and hindrances during migration can decrease fitness, artificial lights present a potentially heightened conservation concern for migratory bird populations. [ABSTRACT FROM AUTHOR]

The current network of weather surveillance radars within the United States readily detects flying birds and has proven to be a useful remote-sensing tool for ornithological study. Radar reflectivity measures serve as an index to bird density and have been used to quantitatively map landbird distributions during migratory stopover by sampling birds aloft at the onset of nocturnal migratory flights. Our objective was to further develop and validate a similar approach for mapping wintering waterfowl distributions using weather surveillance radar observations at the onset of evening flights. We evaluated data from the Sacramento, CA radar (KDAX) during winters 1998-1999 and 1999-2000. We determined an optimal sampling time by evaluating the accuracy and precision of radar observations at different times during the onset of evening flight relative to observed diurnal distributions of radio-marked birds on the ground. The mean time of evening flight initiation occurred 23 min after sunset with the strongest correlations between reflectivity and waterfowl density on the ground occurring almost immediately after flight initiation. Radar measures became more spatially homogeneous as evening flight progressed because birds dispersed from their departure locations. Radars effectively detected birds to a mean maximum range of 83 km during the first 20 min of evening flight. Using a sun elevation angle of -5° (28 min after sunset) as our optimal sampling time, we validated our approach using KDAX data and additional data from the Beale Air Force Base, CA (KBBX) radar during winter 1998-1999. Bias-adjusted radar reflectivity of waterfowl aloft was positively related to the observed diurnal density of radio-marked waterfowl locations on the ground. Thus, weather radars provide accurate measures of relative wintering waterfowl density that can be used to comprehensively map their distributions over large spatial extents. [ABSTRACT FROM AUTHOR]

Predicting species presence requires knowledge of detection of individuals, scale of model variables, model selection uncertainty, and spatial autocorrelation. Our objective was to incorporate recent modeling advances to predict potential habitat occupancy of northern bobwhite (Colinus virginianus). From 15 May-15 August 2008 and 2009, we conducted repeat-visit surveys at 360 sites within Delaware to sample presence of bobwhite. We randomly selected half the data to model scale-dependent relationships of bobwhite presence with metrics of landscape- and site-scale habitat composition and configuration. The final averaged habitat-occupancy model fit the remainder testing dataset with an area under the receiver operating characteristic curve value of 0.62. At the site scale, bobwhite presence was negatively related to interspersion and juxtaposition of early successional habitat (ESH; grassland and shrubland), ESH to forest edge density, and agriculture to forest edge density, though relative effect sizes were weak to moderate after accounting for model selection uncertainty. At the landscape scale, bobwhite presence was negatively related to patch cohesion of human development within 2.5 km and positively related to patch cohesion of ESH within 2.0 km, with both variables exerting strong effects. Bobwhite presence was also weakly and positively related to percentage of shrubland habitat within 1.0 km of the sampling point. We applied our habitat occupancy model to map the predicted presence of breeding bobwhite within the Delmarva Peninsula, USA. The modeling results and distribution map will provide guidance to State and Federal private land management programs in the Mid-Atlantic to identify where habitat management efforts will be most effective. Our methodology can also serve as a basis for future habitat modeling of bobwhite and other grassland-shrubland species across their range. [ABSTRACT FROM AUTHOR]

Increasingly, data from weather surveillance radars are being used by biologists investigating the ecology and behavior of birds, insects, and bats in the aerosphere. Unfortunately, these radars quantify echoes caused by layered biological targets such as migrating birds in a manner that introduces bias in radar measures. We investigated the performance of a bias-adjustment algorithm that adjusts radar measures for vertical variation of reflectivity, nonstandard beam refraction, and spatial displacement of radar targets. We evaluated the efficacies of four variations of this algorithm by their ability to increase correspondence between radar reflectivity measured at two weather radar sites and the ground density of migrating birds measured during two autumn seasons and two spring seasons among 24 hardwood forest sites along the northern coast of the Gulf of Mexico. The algorithm integrated close-range reflectivity data from the five lowest elevation angle sweeps to derive high-resolution vertical profiles of reflectivity (VPRs) that closely corresponded to the observed vertical target density profiles based on a vertically oriented portable radar. The radar reflectivity of birds aloft near the onset of migratory flight was positively correlated with the bird density on the ground. All four radar data adjustment schemes that we tested produced significant improvement in the accuracy of bird density estimates relative to unadjusted radar data. In general, adjusting reflectivity based solely on the VPRs derived using observed refractive conditions yielded the most accurate radar-based estimates of bird density. [ABSTRACT FROM AUTHOR]

Most of our understanding of habitat use by migrating land birds comes from studies conducted at single, small spatial scales, which may overemphasize the importance of intrinsic habitat factors, such as food availability, in shaping migrant distributions. We believe that a multi-scale approach is essential to assess the influence of factors that control en route habitat use. We determined the relative importance of eight variables, each operating at a habitat-patch, landscape, or regional spatial scale, in explaining the differential use of hardwood forests by Nearctic-Neotropical land birds during migration. We estimated bird densities through transect surveys at sites near the Mississippi coast during spring and autumn migration within landscapes with variable amounts of hardwood forest cover. At a regional scale, migrant density increased with proximity to the coast, which was of moderate importance in explaining bird densities, probably due to constraints imposed on migrants when negotiating the Gulf of Mexico. The amount of hardwood forest cover at a landscape scale was positively correlated with arthropod abundance and had the greatest importance in explaining densities of all migrants, as a group, during spring, and of insectivorous migrants during autumn. Among landscape scales ranging from 500 m to 10 km radius, the densities of migrants were, on average, most strongly and positively related to the amount of hardwood forest cover within a 5 km radius. We suggest that hardwood forest cover at this scale may be an indicator of habitat quality that migrants use as a cue when landing at the end of a migratory flight. At the patch scale, direct measures of arthropod abundance and plant community composition were also important in explaining migrant densities, whereas habitat structure was of little importance. The relative amount of fleshy-fruited trees was positively related and was the most important variable explaining frugivorous migrant density during autumn. Although constraints extrinsic to habitat had a moderate role in explaining migrant distributions, our results are consistent with the view that food availability is the ultimate factor shaping the distributions of birds during stopover. [ABSTRACT FROM AUTHOR]

Features a study that examined nest predation in a Louisiana pine forest from 1997 to 1998 through comparison of predation between artificial and natural open-cup nests. Significance of artificial-nest experiments on nest predation studies; Methodology of the study; Results and discussion; Conclusion.

ABSTRACT Identifying features of breeding habitat that influence occupancy and modeling the distribution of grassland birds is needed to direct conservation efforts to reduce population declines associated with habitat loss and fragmentation. Many recent studies on grassland bird habitat use incorporate both local and landscape attributes. However, few studies have determined the appropriate spatial scales at which to measure these relationships. We conducted roadside point counts within Delaware, USA, to determine the presence of grasshopper sparrows ( Ammodramus savannarum). We quantified both land cover composition and configuration at local and landscape scales at our survey sites using data from the National Oceanic and Atmospheric Administration Coastal Change Analysis Program. We determined the spatial scales at which grasshopper sparrow presence was most strongly related to landscape metrics and modeled grasshopper sparrow habitat occupancy at multiple scales, while accounting for variation in detection. At the site scale, occupancy was negatively related to forest and shrub composition. At the landscape scale, grasshopper sparrow occupancy was positively related to the amount of grasslands and pastures, and negatively related to mean inter-patch distance of grasslands and amount of low-intensity development. Our model had good predictive accuracy (area under the receiver operating characteristics curve = 0.717). We present our predictive model applied to the Delmarva Peninsula, USA. © 2013 The Wildlife Society. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) on tall or upward-pointed lighting installations affects the flight behavior of night-migrating birds. We hypothesized that common low-rise lights pointing downward also affect the movement of nocturnal migrants. We predicted that birds in flight will react close to low-rise lights, and be attracted and grounded near light sources, with a stronger effect on juveniles during their autumn migration. We conducted a controlled longitudinal experiment with light-emitting diode floodlights and considered nearby structures that turn on lights at night. We analyzed 1501 high-resolution 3D nocturnal flight paths of free-flying migrants and diurnally captured 758–2009 birds around experimental lights during spring and autumn 2016, and spring 2017. We identified change points along flight paths where birds turned horizontally or vertically, and we considered these indicative of reactions. Flight paths with and without reactions were generally closer to our experimental site in spring than in autumn when the lights were on. Reactions were up to 40% more likely to occur in autumn than in spring depending on the threshold magnitude of turning angle. Reactions in spring were up to ∼60% more likely to occur at ∼35 m from the lights than at >1.5 km. In autumn, some vertical reactions were ∼40% more likely to occur at ∼50 m from the lights than at >2.2 km. Interactions between distance to lights and visibility or cloud cover were consistent with known effects of ALAN on nocturnal migrants. Under poor visibility, reactions were up to 50% more likely to occur farthest from structures in spring, but up to 60% more likely to occur closest to lights in autumn. Thus, the effects of ALAN on night-migrating land birds are not limited to bright lights pointing upward or lights on tall structures in urban areas. Diurnal capture rates of birds were not different when lights were on or off for either season. To our knowledge, this is the first study to show that low-rise lights pointing downward affect night-migrating birds. Although the interpreted reactions constitute subtle modifications in the linearity of flight paths, we discuss future work that could verify whether the protection of nocturnal migrants with lights-out programs would have greater impact if implemented beyond urban areas and include management of low-rise lights. [ABSTRACT FROM AUTHOR]

Migrating birds require en route habitats to rest and refuel. Yet, habitat use has never been integrated with passage to understand the factors that determine where and when birds stopover during spring and autumn migration. Here, we introduce the stopover‐to‐passage ratio (SPR), the percentage of passage migrants that stop in an area, and use 8 years of data from 12 weather surveillance radars to estimate over 50% SPR during spring and autumn through the Gulf of Mexico and Atlantic coasts of the south‐eastern US, the most prominent corridor for North America's migratory birds. During stopovers, birds concentrated close to the coast during spring and inland in forested landscapes during autumn, suggesting seasonal differences in habitat function and highlighting the vital role of stopover habitats in sustaining migratory communities. Beyond advancing understanding of migration ecology, SPR will facilitate conservation through identification of sites that are disproportionally selected for stopover by migrating birds. [ABSTRACT FROM AUTHOR]

Migratory animals are affected by various factors during their journeys, and the study of animal movement by radars has been instrumental in revealing key influences of the environment on flying migrants. Radars enable the simultaneous tracking of many individuals of almost all sizes within the radar range during day and night, and under low visibility conditions. We review how atmospheric conditions, geographic features and human development affect the behavior of migrating insects and birds as recorded by radars. We focus on flight initiation and termination, as well as in‐flight behavior that includes changes in animal flight direction, speed and altitude. We have identified several similarities and differences in the behavioral responses of aerial migrants including an overlooked similarity in the use of thermal updrafts by very small (e.g. aphids) and very large (e.g. vultures) migrants. We propose that many aerial migrants modulate their migratory flights in relation to the interaction between atmospheric conditions and geographic features. For example, aerial migrants that encounter crosswind may terminate their flight or continue their migration and may also drift or compensate for lateral displacement depending on their position (over land, near the coast or over sea). We propose several promising directions for future research, including the development and application of algorithms for tracking insects, bats and large aggregations of animals using weather radars. Additionally, an important contribution will be the spatial expansion of aeroecological radar studies to Africa, most of Asia and South America where no such studies have been undertaken. Quantifying the role of migrants in ecosystems and specifically estimating the number of departing birds from stopover sites using low‐elevation radar scans is important for quantifying migrant–habitat relationships. This information, together with estimates of population demographics and migrant abundance, can help resolve the long‐term dynamics of migrant populations facing large‐scale environmental changes. [ABSTRACT FROM AUTHOR]

Background: Forests in urban landscapes differ from their rural counterparts in ways that may alter vector-borne disease dynamics. In urban forest fragments, tick-borne pathogen prevalence is not well characterized; mitigating disease risk in densely-populated urban landscapes requires understanding ecological factors that affect pathogen prevalence. We trapped blacklegged tick (Ixodes scapularis) nymphs in urban forest fragments on the East Coast of the United States and used multiplex real-time PCR assays to quantify the prevalence of four zoonotic, tick-borne pathogens. We used Bayesian logistic regression and WAIC model selection to understand how vegetation, habitat, and landscape features of urban forests relate to the prevalence of B. burgdorferi (the causative agent of Lyme disease) among blacklegged ticks. Results: In the 258 nymphs tested, we detected Borrelia burgdorferi (11.2% of ticks), Borrelia miyamotoi (0.8%) and Anaplasma phagocytophilum (1.9%), but we did not find Babesia microti (0%). Ticks collected from forests invaded by non-native multiflora rose (Rosa multiflora) had greater B. burgdorferi infection rates (mean = 15.9%) than ticks collected from uninvaded forests (mean = 7.9%). Overall, B. burgdorferi prevalence among ticks was positively related to habitat features (e.g. coarse woody debris and total understory cover) favorable for competent reservoir host species. Conclusions: Understory structure provided by non-native, invasive shrubs appears to aggregate ticks and reservoir hosts, increasing opportunities for pathogen transmission. However, when we consider pathogen prevalence among nymphs in context with relative abundance of questing nymphs, invasive plants do not necessarily increase disease risk. Although pathogen prevalence is greater among ticks in invaded forests, the probability of encountering an infected tick remains greater in uninvaded forests characterized by thick litter layers, sparse understories, and relatively greater questing tick abundance in urban landscapes. [ABSTRACT FROM AUTHOR]

The dynamic weather conditions that migrating birds experience during flight likely influence where they stop to rest and refuel, particularly after navigating inhospitable terrain or large water bodies, but effects of weather on stopover patterns remain poorly studied. We examined the influence of broad-scale weather conditions encountered by nocturnally migrating Nearctic-Neotropical birds during northward flight over the Gulf of Mexico (GOM) on subsequent coastal stopover distributions. We categorized nightly weather patterns using historic maps and quantified region-wide densities of birds in stopover habitat with data collected by 10 weather surveillance radars from 2008 to 2015. We found spring weather patterns over the GOM were most often favorable for migrating birds, with winds assisting northward flight, and document regional stopover patterns in response to specific unfavorable weather conditions. For example, Midwest Continental High is characterized by strong northerly winds over the western GOM, resulting in high-density concentrations of migrants along the immediate coastlines of Texas and Louisiana. We show, for the first time, that broad-scale weather experienced during flight influences when and where birds stop to rest and refuel. Linking synoptic weather patterns encountered during flight with stopover distributions contributes to the emerging macro-ecological understanding of bird migration, which is critical to consider in systems undergoing rapid human-induced changes. [ABSTRACT FROM AUTHOR]

The distributions of birds during migratory stopovers are influenced by a hierarchy of factors. For example, in temperate regions, migrants are concentrated near areas of bright artificial light at night (ALAN) and also the coastlines of large water bodies at broad spatial scales. However, less is known about what drives broad-scale stopover distributions in the tropics. We quantified seasonal densities of nocturnally migrating landbirds during spring and fall of 2011–2015, using two weather radars on the Yucatan peninsula, Mexico (Sabancuy and Cancun). We tested the influence of environmental predictors in explaining broad-scale bird stopover densities. We predicted higher densities in areas (1) closer to the coast in the fall and farther away in spring and (2) closer to bright ALAN and with lower ALAN intensity in both seasons. We found that birds were more concentrated near the coastline in the fall and away from it in spring around Cancun but not Sabancuy. Counter to our expectations, we detected increased bird densities with increased distance from lights in spring around Sabancuy, and in both seasons around Cancun, suggesting avoidance of bright areas during those seasons. This is the first evidence of broad-scale bird avoidance of bright areas during stopover. [ABSTRACT FROM AUTHOR]