4th International Radar Aeroecology Conference


Navigating transitions in the US Central Flyway: does bird migration track seasonal phenologies across latitudes and decades?

Carrie Ann Adams; Monika A. Tomaszewska; Geoffrey M. Henebry; Kyle G. Horton

Understanding the relationship between songbird migration and environmental cues is crucial for assessing the impacts of climate change on avian life histories. We quantified the seasonal timing, or phenologies, of bird migration through the US Central Flyway using 10%, 50%, and 90% cumulative passage dates at 53 weather surveillance radar stations. First, we investigated the synchronization of these migration phenologies with the seasonal transition in environmental conditions across latitudes, including temperature, greenness, relative humidity, and land surface green-up/dormancy. Contrary to expectations, spring migrants did not track any conditions across latitudes. Peak migration passed the southern US about 55 days after green-up and passed closer to green-up at higher latitudes, coinciding with green-up at 48˚N. This finding suggests that they minimized time spent on migration and optimized arrival phenology rather than tracking resource peaks en route. Conversely, peak fall passage occurred approximately 30 days before dormancy across all latitudes. Fall migration may have tracked a specific vegetation phenophase, such as fruiting, as it progressed south. Second, we investigated how the conditions experienced by migrating birds have changed over two decades. Despite long-term advancements and year-to-year plasticity in migration phenology, there were substantial long-term trends in temperature and land surface phenophases experienced by migrants. Temperatures on spring 10% passage dates increased, while 50% and 90% passage occurred closer to green-up. Temperatures also increased on fall 50% and 90% passage dates. For migratory birds, phenological adaptation has not been sufficient to mitigate climate changes within the flyway that may impact resource availability.

Phenology of swallow and martin roosting behavior in the Amazon Rainforest

Maria Carolina T. D. Belotti; Carlos Augusto Morales Rodriguez; Kyle G. Horton

Some species of swallows and martins (Hirundinidae) congregate in large non-breeding aggregations throughout the Americas. These roosts typically occur for several days in the same place and at the same time of the year and disappear suddenly as the birds continue their migratory journeys. In the Amazon Rainforest, however, there are reports of large communal roosts gathering several species of Hirundinidae throughout the year. Because this region hosts migrating swallows and martins from the Nearctic-Neotropical and the Austral migratory systems, resident species may share these roosts with populations from both systems during separate times of the year, indirectly linking the two migratory systems. Because of the high biomass density of these aggregations, we can systematically observe them using data collected by the operational S-band Doppler weather radar located in Manaus (3°08’56.0″S, 59°59’29.1″W) and controlled by the Amazon Protection System (SIPAM) of the Brazilian government. We used two years (2014, 2015) of data collected by this radar to characterize temporal and spatial patterns of roosting activity and investigate whether there is evidence of two well-defined roosting activity peaks corresponding to species’ arrival from each migration system. We processed radar scans within two hours of local sunrise and manually annotated roost detections, drawing bounding boxes around each roost. We then used reflectivity measurements within the bounding boxes to obtain relative estimates of roost size throughout the year. In our presentation, we will describe the technical specifications of Brazil’s weather radar network and present our findings on the seasonal activity patterns within the Amazonian roosts.

Radar-informed aeroconservation: practices, challenges and possibilities

Maja Bradarić; Bart Hoekstra; Bart Kranstauber; Emiel van Loon; Judy Shamoun-Baranes

Calls for aeroconservation have been growing in the recent decade, prompted by an increase in anthropogenic clutter in the airspace. High-rise buildings, aircraft, drones, power lines and wind turbines all pose a threat to aerial wildlife through collisions, habitat fragmentation, and barrier effects. Many of these threats can be minimized with proper conservation plans, and the latest research is highlighting the crucial role that radars can play in informing conservation management. However, implementing research-suggested practices into relevant aeroconservation plans remains challenging, mainly due to the pace of anthropogenic change. Here, we use case studies in the Netherlands to demonstrate how radar-based research has informed spatial planning of future wind farms, onshore and offshore wind turbine curtailments and aviation safety. We demonstrate collaboration with stakeholders, the design of conservation actions and their execution while reflecting on various challenges, from working with data of limited temporal coverage to logistical hurdles of translating science into policy. Based on the experience gained through these projects, we discuss future research directions in applied radar aeroecology.

Daily post-breeding flight activity over the open ocean by Purple Martins revealed through radar and telemetry

Jeffrey J. Buler; Katherine Bird; Steve Cottrell; Ian Stewart

The Purple Martin (Progne subis) is the largest migratory swallow in North America and forms large communal roosts during late summer before migrating to South America in autumn. Our objective was to highlight post-breeding season observations of Purple Martins using the open ocean offshore during the day. We defined “offshore” as >18 km from shore (i.e., distance that birds can see to the horizon from 25 m ASL). We tracked the post-breeding movements of individual martins using radio telemetry and the Motus Wildlife Tracking System. We tagged 152 adult and juvenile martins among four breeding colonies in southeastern PA and northern DE from April – July of 2020-2022 with a CTT LifeTag or HybridTag radio transmitter. We also analyzed weather surveillance radar observations of birds departing communal roosts at sunrise in the mid-Atlantic region from the KDOX (Dover, DE) and KAKQ (Norfolk, VA) radars during July – September 2020-2022. In 2022, radio-tagged martins were detected at four coastal receivers departing nearby roosts around sunrise (range = 3 to 10 unique birds per receiver). Three martins were detected on six different days at a receiver located 42 km offshore of Virginia Beach, VA. Radars detected thousands of martins flying out to ~50 km offshore over the Atlantic Ocean at high altitudes (1 – 4 km ASL) when departing roosts daily at sunrise. Purple Martins regularly traveled far offshore over the Atlantic Ocean during the day after sunrise departure from coastal communal roosts, presumably to forage on aerial insects. Locally breeding martins traveled widely amongst these roosts during late July through early September before migrating farther south. More study is needed to understand open ocean insect activity and foraging behavior of martins.

Factors influencing spatial patterns in migratory landbird stopover across Texas and Louisiana, USA

Amanda Y. Crandall; Jeffrey J. Buler; Jaci A. Smolinsky; Lori A. Randall; R. Randy Wilson; T.J. Zenzal Jr.

Texas (TX) and Louisiana (LA) comprise a large and diverse landscape that the U.S. North American Bird Conservation Initiative delineates into ten ecologically distinct Bird Conservation Regions (BCRs) based on similar biotic and abiotic factors. Billions of landbirds stopover in these regions each migration season to rest and refuel. Yet, nonstationarity in how stopover distribution patterns are related to land cover, climate, and anthropogenic factors remain understudied, particularly for areas of TX and LA away from the Gulf of Mexico coast. Using 13 years of data collected from 15 weather surveillance radars, we quantified the density of migratory birds departing from stopover sites at a 250 m spatial resolution. We fit boosted regression tree (BRT) models among an ensemble of 196 overlapping modeling frames (400 x 400 km extent) stratified across TX and LA to determine relative importance and relationships between 26 environmental predictor variables and seasonal mean bird density. The top-ranking covariates varied with bird density across space, between BCRs, and sometimes between seasons in respect to the direction and strength of their linear relationships. Across most modeling frames temperature, precipitation, distance to artificial light at night (ALAN), and east-west windspeed ranked highly, reflecting the importance of climate in predicting spatial distributions of birds. We also found evidence that bird responses to light differ based on scale and composition of the surrounding landscape. Specifically, there is general attraction to bright light at the broad scale and avoidance of bright light at the fine scale. These relationships varied among BCRs and with the mean distance to ALAN across the landscape. Such nonstationarity in our results mirror the complex interactions between climate, land cover, and other factors that influence bird stopover distributions across TX and LA.

Differences in terrestrial versus offshore songbird migration: Implications for offshore wind energy development and operations

Shannon R. Curley; Andrew Farnsworth; Adriaan M. Dokter; Timothy P. White

Every year, 2.5-5 billion birds embark on nocturnal migrations over the contiguous USA, including movements that take birds over water. Offshore movements are difficult to investigate due to remoteness and lack of monitoring infrastructure. Knowing the timing, locations and numbers of birds moving offshore, can inform collision mitigation and identify high-risk areas where birds can potentially interact with offshore wind. We used 15 coastal weather radars (WSR) in the western North Atlantic and Gulf of Mexico to evaluate differences in passage, altitude, and timing of migration between adjacent terrestrial and offshore habitats for spring and fall from 2014 to 2024. We used machine learning to predict unobserved low altitude densities that the radar beam may overshoot at increasing distances from the radar. We estimate 82.5 million birds/km cross the 15 radars each year with approximately 23.4 million birds/km in the offshore environment. Offshore flight altitudes were lower in both seasons by 167 m and 52 m in spring and fall, respectively. Approximately 9.4 million birds/km fly at altitudes lower than the rotor-swept zone (below 300m). Additionally, the duration of offshore cumulative migration traffic occurs on approximately half as many nights than terrestrial migration. These findings can provide essential guidance for identifying high-risk areas and times to help guide mitigation strategies to limit potential bird-wind turbine interactions during development, pre- and post-construction, operational and maintenance phases and can be implemented in developing offshore migration forecasts.

Mexican free-tailed bats nightly emergence, migration phenology, and population dynamics in south-central Texas

Yuting Deng; Caitlin J. Campbell; Maria C.T.D. Belotti; Wenlong Zhao; Gustavo Perez; Sam Simon; Meredith Nash-Martin; Elske K. Tielens; Daniel R. Sheldon; Subhransu Maji; Jeffrey F. Kelly; Kyle G. Horton

Insectivorous bats play a key role in the ecosystem and agroecology, providing services for pest control and serving as ecotourism attractions. In Texas, this is especially true, as Mexican free-tailed bats (Tadarida brasiliensis) have one of the densest aggregations of mammals anywhere on the planet. However, their migration, population, and foraging ecology in this region are understudied, with the majority of knowledge coming from just a few dense colonies. Little is known about the neighboring cave and bridge colonies throughout the south-central Texas region. Nightly, millions of bats emerge from colonies to forage around sunset — these dense aggregations in the aerial space can be captured by weather radar. We used an AI-assisted system to detect and track roost emergence automatically, with manual screening to ensure data quality. In this study, we utilized four weather surveillance radars (2000 – 2022) in south-central Texas to establish a robust quantification of free-tailed bats’ (1) timing of nightly emergence, (2) long-term phenology of different life-history phases (i.e., spring arrival, parturition, pup flight, fall migration), and (3) population trends. Moreover, we investigated how the annual timing of different life history phases changed in the face of climate and local weather by incorporating drought, temperature, humidity, precipitation, and wind data in the analyses. Our study sheds light on the plasticity of seasonal migration and nightly emergence timing of insectivorous bats under the impact of climate change, as well as filling in knowledge gaps in Mexican free-tailed bats’ regional population status.

Quantifying bird movements displayed on the polarimetric WSR-88D: The importance of the differential phase product

Sidney Gauthreaux; Dave Mayer; Elizabeth Woodworth; Edwin Herricks

The product, differential phase, produced by the polarimetric WSR-88D can be used to separate bird and insect scatterers aloft and to determine the body orientation (heading) of migrating birds. The product has also been used to quantify the reflectivity backscattered from migrating birds (Gauthreaux et al. 2019) by selection of resolution volumes of reflectivity produced by birds based on the associated values of the polarimetric variable, backscatter differential phase (δ) reported for bird scatterers. In this presentation we compare the estimates of the amount of nocturnal bird migration detected by the Dallas-Fort Worth WSR-88D (KFWS) during three spring seasons near midnight generated by the differential phase method to those produced by the bioRad method that selects resolution volumes of backscattered reflectivity based on the radial velocity of migrating birds. Even though the WSR-88D collects reflectivity and radial velocity products at different times, the similarity between the estimates of bird reflectivity generated by the two methods is highly significant, and further supports the use of polarimetric weather radar for the quantification of the reflectivity backscattered from migrating birds aloft.

Stopover ecology and conservation of migratory landbirds in the eastern United States

Fengyi Guo; Jeffrey J. Buler; Kyle G. Horton; Adriaan M. Dokter; Emily B. Cohen; Daniel Sheldon; Jaclyn A. Smolinsky; David S. Wilcove

Migratory landbirds are experiencing dramatic population declines in North America, but little is known about the important habitats they use as stopover sites during migration. We used data from weather surveillance radar to map seasonal stopover densities of landbirds across the eastern U.S. during spring and autumn migrations. We identified stopover hotspots covering 2.47 million hectares that consistently support high densities of migrants across years. However, only 16.7% of these sites are hotspots in both seasons. Deciduous forest is the most important habitat type, with high concentrations of birds in forest fragments embedded in broadly deforested regions, especially in spring. While protected areas have higher stopover densities of birds, only 1/3 of hotspots are covered, and many of these protected areas are still subject to extractive uses. We also found evidence that the agricultural Midwest is an anthropogenic migration barrier for many landbirds, affecting their flight and stopover patterns. In summary, a well-distributed network of well-protected stopover areas, complementing conservation efforts on the breeding and wintering grounds, is essential to sustaining healthy populations of migratory landbirds in North America.

Quantification of migratory insect movements across the Strait of Gibraltar

Birgen Haest; Will L. Hawkes; Alejandro Onrubia; Silke Bauer

Insect migration is a widespread phenomenon occurring on enormous scales and over vast distances. The movements of these trillions of individuals result in huge biomass, nutrient, and energy transfers, impact crop production, spread diseases, as well as provide important ecosystem services such as pollination. The spatiotemporal dynamics of these global movements, however, remain largely unknown. We quantified migratory insect movements across the Strait of Gibraltar with a vertical-looking Birdscan MR1 radar. This passage is the narrowest stretch of the western Mediterranean Sea, connecting the European and African continent, and a key migratory route for birds. In this talk, we characterise and quantify aerial migratory insect movements and directions during spring and summer of 2023, including variations in diel and seasonal activity and insect community composition. This quantification of overall insect migration across the Strait of Gibraltar, fills a knowledge gap on the scale of migratory movements between the African and European continent.

Improving ecology approaches for detecting flying animals from weather radar with machine learning

Mubin. U. Haque; J. Dabrowski J; R. Rogers; H. Parry

Monitoring flying animals such as birds, bats, and insects is important to ecologists for understanding their behaviour and managing the environment. Such animals can be detected and tracked with Weather Radar (WR) data. Detections are commonly achieved by thresholding WR variables at specific values that are determined by ecological expert data analysis. The thresholding approach is however typically over-sensitive (high recall) where it is good at identifying animal movement activities but is also prone to produce many false positive detections. False positives pose significant consequences in detecting the movement of flying animals. They can lead to wastage of resources in pest control efforts, loss of energy production due to unnecessary wind turbine shutdowns to avoid collisions, and misinterpretation of migration patterns, affecting management decisions, among other consequences. To overcome the over-sensitivity, we combine the ecologist’s thresholding approach with machine learning to produce an approach that is both accurate and robust to false positive detections. In this approach, we begin by training (or pre-training) a machine learning model to mimic the thresholding approach on a very large and diverse dataset of WR images. The ecologist’s thresholding model can thus be seen to “teach” the machine learning model how to detect animal movement. However, the machine learning model will also learn the thresholding model’s weakness and produce many false positives. We then correct this by fine-tuning the machine learning model on a small dataset where animal movement has been manually labelled by a human expert. We find that our fine-tuned machine learning model can both minimize the need for labelled data and improve on the thresholding approach. This improvement is exhibited by a good balance between sensitivity and precision where our model is good at detecting animals and does not produce many false positive detections.

Examining waterfowl distributions with NEXRAD for nationwide conservation and food security

Matthew J. Hardy; Jeffrey J. Buler; Christopher K. Williams; Brian S. Ladman

The Central Valley of California (CVC) and Mid-Atlantic (MA) regions of the U.S. are critical sites for waterfowl species in the winter, providing feeding and roosting locations for many species. Mapping waterfowl distributions using NEXRAD aids in the targeted adaptive management of important waterfowl habitat. Additionally, mapping waterfowl distributions on a broad scale may allow various government agencies to better understand the interface between wild and domestic birds and commercial agricultural practices. We used 9 years (2014–2023) of data from the US NEXRAD network to model winter waterfowl relative abundance in the CVC and MA as a function of weather, temporal, and environmental characteristics using Boosted Regression Tree modelling. We were able to quantify the variability in effect size of 28 different covariates across space and time within two geographic regions which are critical to nationwide waterfowl management and host a high density of nationally important commercial agriculture. In general, environmental and geographic predictors had the strongest relative effect on predicting wintering waterfowl relative abundance in both regions, while effects of land cover composition were more regionally and temporally specific. Our findings promote a better understanding of spatiotemporal associations of waterfowl to landscape features and may aid in conservation and biosecurity management protocols.

Linking the occurrence of migratory insects to the abundance of insectivorous birds

Will L Hawkes; Fabienne Sellinger; Oskars Keišs; Birgen Haest

Insect migration is thought to be the most important terrestrial movement of animals globally. They migrate in their trillions along routes thousands of kilometres long, transferring huge amounts of biomass, nutrients, and energy as they do so. These insects are pest-controllers, decomposers, pests, disease vectors, and crucial pollinators. However, despite their great importance to the continuing function of the planet’s ecosystems, vanishingly little is known about them. This is an especially pertinent area of research as it is thought that many insectivorous birds rely on the migratory insects as an important food source. Here, we combine a vertical-looking Birdscan MR1 radar with ground-level insect monitoring techniques to quantify insect migration along the coast of Latvia. We present data on the relationship between migratory insect and bird movements, while also analysing the relationship between ground level and high-altitude insect migration. Our results contribute understanding of the intricate links between different migratory taxa, with the potential to aid conservation and agricultural practices alike.

Niche model applications in radar aeroecology

Samuel J. I. Hodges; Ryan R. Neely III; Christopher Hassall

I will present current and future applications of environmental niche models in my research of insect aeroecology, in the United Kingdom. Niche modelling has become a popular tool in ecological sciences for understanding species spread and evolution of range boundaries in changing environments. More recently, these tools have been applied in conjunction with current climate change science to understand how vulnerable species and pest species will respond to human induced climate change. These changes have consequences for the future of human agriculture, medicine, and conservation efforts. Radar aeroecology presents a unique opportunity in remote sensing of species presence, for its ability to sample wide ranges of space in the horizontal (weather radar) and vertical (vertical-looking radar) domains. Combined with existing national weather radar networks, this would provide an unprecedented level of coverage for insect presence-absence sampling, at high spatial and temporal resolution. This data can be used with environmental niche models to increase our understanding of the spread of high-flying, long-distance-dispersal taxa, as well as the atmospheric conditions associated with flight. When coupled with dispersal models, radar aeroecology and niche modelling have the potential to definitively demonstrate the airspace as a biological habitat, and forecast future insect dispersal events.

Radar-based mapping of migratory birds for nature-inclusive wind energy

Bart Hoekstra; Stacy Shinneman; Johannes De Groeve; Berend Wijers; Bart Kranstauber; Judy Shamoun-Baranes

The millions of birds migrating over the Netherlands each spring and autumn are increasingly navigating a landscape filled with energy infrastructure. In particular, installed wind energy capacity is set to increase dramatically in the upcoming decades, impacting birds both off- and onshore through barrier effects and (fatal) collisions. While mitigation measures for these effects after construction of wind parks exist, avoiding such aerial conflicts altogether is difficult with limited information on the spatial distribution of birds. Migratory birds are considered in environmental impact assessments, but they are difficult and expensive to study, especially at night and at the scale and pace of the energy transition. We present how continuous monitoring of the Dutch airspace by weather and bird radars can be used to quantify spatial patterns of bird migration at altitudes relevant to wind energy. By aggregating radar measurements gathered during peak migratory movements across 6 years of radar observations, we have created the first high-resolution, spatially-continuous maps of migratory movements of birds covering much of the Netherlands. These maps were developed in collaboration with and for policy makers to aid in the site-selection process and mitigation decision making.

Characterization of the North American aerial migratory niche

Silvia Giuntini, Carolyn S. Burt, Annika L. Abbott, Carrie Ann Adams, Maria C. T. D. Belotti, Yuting Deng, Miguel F. Jimenez, Jeffrey F. Kelly, Subhransu Maji, Meredith Nash-Martin, Sam Simon, Daniel Sheldon, Kyle G. Horton

Earth’s lower atmosphere is a vital ecological habitat, home to trillions of organisms that live, forage, and migrate through this medium. Despite its importance, this space is seldom considered a primary habitat for ecological or conservation prioritization, making it one of the least studied environments. However, it plays a crucial role as a global conduit for the transfer of biomass, weather, and inorganic materials. Fundamental research is essential to address core ecological questions and to understand this habitat’s intricate spatial and temporal structure. To achieve this, we analyzed over 108 million 5-minute radar scans from 143 NEXRAD sites, focusing on 24-hour diel cycles across the contiguous United States. This extensive dataset, spanning from 1995 to 2022, allowed us to quantify aerial niche space by systematically identifying peak activity times, the vertical airspace that contained 50% of migration activity, and the percent of passage across diurnal and nocturnal diel cycles. We reveal that airspace usage dominates during nocturnal periods during both spring and fall (88%), while summer exhibited a more balanced distribution (54% nocturnal). Additionally, the percent of nocturnal activity increased with latitude in spring and fall but decreased in summer. Peak aerial activity typically occurred about four hours after local sunset in both spring and fall, with variations based on latitude and longitude. During these peak times, on average, half of the aerial movement was confined within a 516-m wide envelope, starting around 355 meters above ground level. Our research underscores the need to view the lower atmosphere as a structured habitat with significant ecological importance.

Radar tracking of birds movement pattern – A case study of coastal airport on birds migration flyway

Lili Jia

Each year, large quantity of shorebirds, passerines and raptors fly across Bobai Bay, located on East Asian-Australasian flyway and West Pacific Flyway, for stopover, breeding and wintering. The increasing aerial traffic volume has intensified the conflict between aircrafts and birds. Recent research on birds movement is mainly on species-specific migration in continental scale, real-time birds movement flux and nocturnal birds movement pattern in and around airports is lack of research in China. We used a set of bird radar to provide real-time birds movement flux for airports, with field observation for validation of species to present birds diurnal and nocturnal movement pattern of abundance and altitude from winter to spring. We found out that birds movement peak time often occurs at sunrise and sunset in winter, nocturnal movement is less frequent than diurnal movement, while in spring, birds movement peak time often occurs after sunrise, and before sunset. Intense migration starts at the end of March and occurs frequently in April and May.The migration often occurs right after sunset and last for several hours till sunrise,with migration peak time varying across days. The majority of birds fly below 200 m from winter to spring, while the proportion of nocturnal flight altitude above 200 m in intense migration days is higher than that in winter.To assess the potential risk of birds collision, we also compared birds movement and runway crossing distribution in high traffic volume and low traffic volume to provide statistic proof for mitigating potential birds strike risk. Reported birds collision incidents in civil aviation occurred more frequently in migration season, therefore, further study into annual birds migration pattern at specific airport location as well as on regional scale with network of radars is needed to present live regional birds migration flux and provide early warning system for airports.

Quantifying range- and topographical biases in weather surveillance radar measures of migratory bird activity

Miguel F. Jimenez; Birgen Haest; Ali Khalighifar; Annika L. Abbott; Abigail Feuka; Tao Liu; Kyle G. Horton

Weather radar systems have become a central tool in the study of nocturnal bird migration. Yet, while studies have sought to validate weather radar data through comparison to other sampling techniques, few have explicitly examined the impact of range and topographical blockage on sampling detection — critical dimensions that can bias broader inferences. Here, we assess these biases with relation to the Cheyenne, WY Next Generation Weather Radar (NEXRAD) site, one of the large-scale radars in a network of 160 weather surveillance stations based in the United States. We compared local density measures collected using a mobile, vertically looking radar with reflectivity from the NEXRAD station in the corresponding area. Both mean nightly migration activity and within night migration activity between NEXRAD and the mobile radar were strongly correlated (r=0.85 and 0.70, respectively), but this relationship degraded with both increasing distance and beam blockage. Range-corrected NEXRAD reflectively was a stronger predictor of observed mobile radar densities than uncorrected reflectivity at the mean nightly scale, suggesting that current range correction methods are somewhat effective at correcting for this bias. This was also true of within night migration activity up to 65km, but beyond this distance, uncorrected reflectivity became a stronger predictor than range-corrected reflectivity, suggesting range limitations to these corrections. Together, our findings further validate weather radar as an ornithological tool, but also highlight and quantify potential sampling biases.

The next generation of aerial biodiversity monitoring

Dominik Kleger; Silke Bauer; Birgen Haest; Felix Liechti

The airspace is a crucial habitat for aerial biodiversity but remains difficult to monitor. Remote sensing approaches like radar have emerged as important tools for large-scale airspace monitoring and can provide data on Essential Biodiversity Variables (EBV), e.g. by quantifying abundances and distributions (‘Species Populations’) and identifying the timing and routes of migrations (‘Species traits’). There are two major systems of radars – large-scale weather radars and small-scale biological radars. Weather radars provide estimates of aerial biomass at continental scales but are limited to higher altitudes (>200 m) and coarse taxonomic information, while small scale vertical-looking radars can provide detailed insights into individual bird, bat and insect movements. Swiss Birdradar Solution has developed a new vertical-looking small-scale radar that is used specifically for an autonomous monitoring of the aerial fauna (birds, bats and insects) in real time. This new radar enables whole new possibilities in terms of classification, quantification and derived features from the detected echoes. This includes 3D tracking of individual targets with high resolution (1.5 m) for an altitude range from 3 up to several hundred metres (insects) or up to a thousand metres (birds, bats). Classification of those echoes is based on various features like size, shape, wing beat pattern and frequency, Micro-Doppler signature and many more. To demonstrate the value of a network based on small scale vertical-looking radars, we present data on abundance and temporal movement patterns of insects from Finland to France. Further efforts are planned within the ongoing project HiRAD to identify and classify taxonomic groups in more details (specifically insects), but also to harmonize weather radar data with small scale radar data.

The importance of upstream environmental cues for predicting bird migration

Bart Kranstauber; Fiona Lippert; Emiel van Loon; Patrick Forré; Bart Hoekstra; Maja Bradarić; Judy Shamoun-Baranes

The intensity of migratory bird movement varies from night to night by an order of magnitude. This variation can be attributed to a host of internal and external factors. For example, weather strongly influences the speed and costs of migration. Consequently, birds need to make weather-dependent decisions both at departure and during their journey while integrating their condition to optimize migration. In recent years, there has been an increasing interest in predicting bird migration to protect migratory birds flying through wind farms and to ensure aviation safety. For accurate predictions, it is critical to consider the environmental predictors used. For example, to capture departure decisions, it is important to include representative conditions from the location where birds decide to depart or defer migration. We discuss different ways of incorporating this information into recently developed predictive models. We find that not only instantaneous local environmental conditions, but also the conditions in the past and at inferred departure locations are important both over land and sea. These ideas are integrated into a spatially explicit machine learning model predicting migration across the United States. To predict the density of migrants the departure and movement processes are modeled separately. We attribute the predictions for these processes to environmental variables, including weather at various altitudes and local conditions like land use and elevation.

Quantifying swallow roost sizes using thermal imagery

Greg W. Mitchell; Jason Duffe; Morgan Hrynyk

Swallows and martins congregate in large nocturnal roosts post-breeding. These roosts are readily detected by weather radars when birds take flight in the morning. To date, the number of birds in a roost is estimated by translating radar reflectivity values to number of birds based on an estimate of the radar cross section of a bird. However, to our knowledge, estimates of the number of birds comprising a roost have never been empirically validated. In this study we tested the ability of a drone mounted thermal imaging camera to detect individual swallows roosting in a wetland at the Big Creek National Wildlife Area, Lake Erie, ON, Canada. In August 2022 we visually confirmed the formation of a large roost of bank swallows at sunset in the wetland. We then flew a drone mounted with a thermal imaging camera between 23:00 and 2:00 am over a ~6.25 km2 area at an altitude of 25 m. We collected 648 adjacent images with 5 cm resolution. We found that birds had readily identifiable thermal signatures. Next, we randomly selected 10% of the images and manually counted the number of birds we observed. Following manual counting, we then applied a top hat filter to the same set of images to identify birds, converted these images to binary images and used a machine learning algorithm to count the number of individual birds. When comparing our manual counts with our automated counts using a linear regression, automated counts slightly underestimated the manual counts (β = 0.84, R2 = 0.61). Over our survey area and using the automated detection and counting algorithm and a correction based on our manual counts, we estimate that there were 36 bank swallows per 100 m2 of vertical vegetation. We conclude that thermal imaging of roosts is a promising method to validate estimates of the number of birds emerging from roosts based on radar reflectivity.

National scale nocturnal arthropod declines unveiled by weather radars

Ryan R. Neely III; Mansi Mungee; Maryna Lukach; Chris Shortall; James R. Bell; Elizabeth J Duncan; Freya Addison; Lee E. Brown; William Kunin; Christopher Hassall

Arthropod declines have been widely reported; however, a lack of comprehensive data has hindered our ability to assess their large-scale generality and drivers. Here, we used a novel and freely available dataset – atmospheric scans from a network of meteorological radars – to quantify high resolution aerial abundance of both, diurnal and nocturnal arthropods across the United Kingdom. Using observations between 2014 and 2021, and covering >42,000 km², we estimated that at least 2.31(±1.28) quadrillion arthropods fly over the UK each year, with high vertical and spatial heterogeneity. Our analysis revealed a widespread decline in nocturnal, but not diurnal arthropods. Furthermore, we observed more pronounced losses in northern latitudes, for both diurnal and nocturnal arthropods, attributed to changes in light pollution, land cover, and weather. While previous studies have reported declines in specific species and places, our study reveals broadscale and widespread losses, especially in the abundance of nocturnal aerial arthropods, and highlights the importance of considering spatial variation in temporal biodiversity trends. Additionally, we demonstrate the potential for weather radar datasets to enhance understanding of biodiversity decline trends and causes at fine resolution across large spatio-temporal extents.

The Aloft data repository for vertical bird profiles of European weather radar data

Cecilia Nilsson; Peter Desmet; Judy Shamoun-Baranes; Bart Kranstauber; Adriaan M. Dokter; Nadja Weisshaupt; Baptiste Schmid; Silke Bauer; Günther Haase; Bart Hoekstra; Nicolas Noe; Stijn Van Hoey; Pieter Huybrechts; Berend Wijers; Hidde Leijnse

A huge benefit of using weather radars for biodiversity monitoring is the large-scale coverage offered by networks of stations. The heterogeneity of the European weather radar network (in hardware, data processing and data availability) has long hampered development of a joint dataset containing biological weather radar data from across Europe. However, long-term and interdisciplinary collaborations, mainly through the ENRAM and GloBAM projects, have now led to the development of the Aloft repository. It is the first public repository of animal movement data derived from European weather radars, available at aloftdata.eu. The animal movement data has been extracted from OPERA supplied polar volumes using vol2bird, and data are stored as vertical profiles (VP) in HDF5 format and in time series of vertical profiles (VPTS) in the VPTS CSV format. Despite strong heterogeneity in coverage and data quality it provides the largest and most complete dataset of its kind in Europe and is updated with new data daily. The repository currently contains data from 151 radar stations in 18 different countries, however the amount of data per station varies greatly, with a maximum of 8 years of data. The repository also provides a visualization tool, CROW, where data in the repository can be explored in an interactive map. I will present the current status of the repository, some examples of ongoing applications, as well as the upcoming challenges posed by planned changes to data storage polices at EUMETNET and OPERA.

Vultures’ foraging network: a century-old hypothesis investigated with radar

Yohan Sassi; Camille Assali; Vincent Liebault; Vincent Delcourt; Martina Scacco; Olivier Duriez; Yann Tremblay

Numerous vultures coming from every direction, falling from the sky in large numbers and aggregating around a carcass is a mesmerising sight. For this phenomenon to occur, it has been hypothesized that two things are required. First, the local enhancement, a social cue due to a vulture’s sharp loss in altitude that conspecifics can rely on to locate unpredictable carrions. Second, the use of a social foraging strategy where individuals spatially distribute themselves in order to form a network in which the interindividual distance allow them to keep an eye on their flying conspecifics. This network foraging strategy has been formulated by Tristram in 1867, but never measured empirically, because of the technical difficulty to record simultaneously the positions of numerous vultures flying at high altitudes. To overcome this challenge, we used a radar to track all birds flying simultaneously into a 6 km radius during 33 days. In parallel, 2300 tracks were annotated with their corresponding species by direct field observation. We used these annotated tracks to train a machine-learning algorithm in order to probabilistically annotate the rest of the dataset. We will present here the first empirical results revealing the modalities of coordinated foraging movement patterns of griffon vultures.

Contributions of local and synoptic weather dynamics over preceding days for enhanced nocturnal bird migration forecasts

Baptiste Schmid; Thibault Désert; Vincent Delcourt; Camille Assali; Cécile Bon; Amédée Roy

The large variations between consecutive nights in the intensity of nocturnal bird migration have been associated with weather conditions to build near real-time bird migration forecast. Existing models have mostly focused on local weather conditions, implicitly assuming influences from large-scale synoptic weather patterns. This study aimed to enhance bird migration forecasts by assessing the contributions of weather dynamics at different spatial and temporal scales. We used vertical bird density data from 9 French weather radars spanning 6 years and employed gradient-boosted regression trees for prediction. The study investigated the contributions of the different meteorological metrics considered using explainable regression trees. This study not only leads to enhanced forecast accuracy, but also contributes to a deeper understanding of the factors influencing bird migration. Local and immediate weather conditions were mostly associated with low migration intensity. In contrast, weather conditions that were spatially distant and from previous days were associated with migration peaks, possibly accounting for the accumulation of migratory birds due to inclement weather. Assessing the relative contributions of local and synoptic weather dynamics deepens our understanding of the underlying migration processes and contributes to a better prediction of the nights with peak migration intensity.

Using weather surveillance radar to map insect takeoff: a case study from the US Plains region

Elske K. Tielens; Jeffrey F. Kelly

Weather surveillance radar has potential as a tool for large scale monitoring of insect biodiversity and abundance. However, its application to conservation, agriculture, and land management is limited by our ability to connect movement of insects in the aerosphere to the underlying landscape. Here we demonstrate the potential as well as challenges of using weather surveillance radar to map ground distributions of insects initiating daytime flight. We provide a case study of diurnal fall insect migration in the Plains region of the US and discuss methods to identify the radar signature of insect departure from the landscape relative to the transmigration phase in dispersal. We focus on fall diurnal insect migration at NEXRAD radar KTLX. During peak migration, the density of insect targets above 500 meters exceeds cumulative density below 500 m, indicating a significant transmigrational component in observed insect flight. We evaluate patterns in insect density and prevailing wind speed and direction to identify disjunctions between low high altitude flight indicative of different insect flight strategies. We find that insect density during takeoff accumulates slowly, while high altitude flight is characterized by a rapid increase in cumulative density. We find that days with unstable atmospheric conditions are characterized by greater layering in flight densities at low elevations. Next, we discuss a spatial approach to differentiate flight initiation from long distance dispersal. The horizontal structure of insects in the air during the takeoff phase is structured to their ground distribution, while the transmigrational phase of flight is coarsely structured. We assess correlations between spatial distributions of insects at low elevation across migration events to identify scans dominated by diurnal takeoff. Lastly we compare low elevation distributions of takeoff to vegetation and land use patterns to demonstrate insights from insect flight initiation mapping.

A post-processing framework for bird radar systems

Jens A. van Erp; E Emiel van Loon; Johannes De Groeve; Maja Bradarić; Judy Shamoun-Baranes

Dedicated bird radars can track individual birds autonomously and are an effective tool for continuous monitoring and quantification of aerial bird movement. Bird radars are deployed for aviation safety, wind energy and conservation and create valuable opportunities for ecological research in both urbanized and remote locations. However, automated tracking algorithms may not provide sufficiently reliable data. Therefore, post-processing is required but often non-trivial due to the size of the data. We present a post-processing framework that implements knowledge of the radar system and bird biology to filter the data and retrieve reliable, high-quality tracking data. The framework is split into three modules, each with a specific aim: (I) sub-setting based on prior knowledge of the radar system and bird flight, (II) improving bird track quality and (III) detecting and removing spatio-temporal sections of data that have a clear bias for false observations. We demonstrate the effectiveness of the framework by implementing it in a highly cluttered environment, an offshore wind park. Our case study compares track densities inside and outside an offshore wind farm using all bird radar tracks and the post-processed tracks and applies the workflow to a dataset of visually validated radar tracks. The framework provides a logical workflow to increase the reliability and quality of a bird radar dataset while being adaptable to the radar system and its surroundings. This is a first step towards standardizing the post-processing methodology for automated bird radar systems, which can facilitate comparative analyses of bird movement in space and time and improve the quality of ecological impact assessments.

Evaluating the potential of nocturnal flight calls in bird migration research by citizen science and weather radar observations

Nadja Weisshaupt; Juha Saari; Jarmo Koistinen

The study of nocturnal bird migration brings observational challenges because of reduced visibility and observability of birds at night. Radars have long been the preferred choice of scientists to study nocturnal migrations. A known challenge in radars is the lack of species-level information. Species-level information is typically required in activities targeting biodiversity questions. With technological advances in recent decades and with improved accessibility and affordability of acoustic tools, bird sound recordings have steeply increased in popularity. In Europe, there is no exhaustive qualitative and quantitative evaluation of the content of such acoustic databases. Therefore, the value of bioacoustics as a complement in radar studies, such as bird collision hazard assessments, is mostly unknown. The present talk contrasts acoustic recordings with citizen science observations and weather radar data to assess the qualitative and quantitative yield of acoustic recordings for migration-related research. Acoustic migration phenologies are compared to citizen science migration schedules. We identify seasonal and annual patterns observed in combined acoustic and radar analyses and discuss underlying behavioural and phenological species-level dynamics. Our study shows that about 70% of the nocturnal long-distance migrant populations and about 50% of the nocturnally migrating passerines in total is migrating silently. Hence, this affected the capacity of acoustic data to represent migrant populations aloft when long-distance migrants dominate the airspace surveilled by weather radar. On the other hand, some highly vocal and numerous species, such as thrushes, may correlate well with weather radar observations if they outweigh the silent migrants during the respective migration season. Overall, the ability of acoustic records to act as a proxy of overall migration dynamics is highly dependent on the migration period and species involved.

Active navigation and meteorological selectivity drive patterns of mass intercontinental insect migration through the Levant

Yuval Werber; Jason Chapman; Don R. Reynolds; Nir Sapir

Insect migration is crucial to many natural processes and human activities yet remains inadequately understood. On the Mediterranean’s eastern shores lies a 70-km wide stretch of hospitable habitat between the sea and the Arabian Desert, which we term the Levantine Corridor, extending 400 km south from Turkey to the edge of the Sahara. We deployed biological radars at seven locations in the corridor over an 8-year period, which recorded 6.7 million large insects (>10 mg) migrating along the corridor, suggesting that this region at the nexus of three continents constitutes a bottleneck on a major insect migration flyway. Our results, documenting the scale of the movements, phenological patterns, and responses to weather, clearly demonstrate the Levantine Corridor’s global importance, funnelling more than 800 million large insects annually. Migrants showed strong migratory directionality in spring and autumn, but migration intensity was erratic, with mass migration events separated by periods of much less intense movements. Migration intensity was strongly dependent on weather, with insects preferentially migrating on occasions with seasonally beneficial tailwinds and warmer temperatures. The study reveals a hitherto unexplored major insect migration flyway through the Levantine Corridor, with implications for food-webs, pollination, disease transmission, pest outbreaks, and species invasions across an enormous area of Western Asia, Eastern Europe, and Northeast Africa.

Hurricane Impacts to Landbirds during Autumn Migration along the Northwestern Gulf of Mexico

Theodore J. Zenzal Jr.; Amanda Y. Crandall; Lori A. Randall; Jaci A. Smolinsky; R. Randy Wilson; Jeffrey J. Buler

Habitats along the northern Gulf of Mexico support high numbers of birds when they stopover in the region to rest and refuel. Stopover habitats are often in areas experiencing human population growth and are impacted by natural disturbances and climate change. Predicted habitat loss from sea level rise and extreme weather events coupled with mismatches in the timing of peak bird migration with food abundance may limit the availability of high-quality habitats. This is expected to be the case in Texas and Louisiana, which support the billions of migratory landbirds that stopover. Understanding how acute effects of climate change (e.g., severe weather events) influence stopover distributions will help identify areas of conservation priority. We investigated how hurricanes have impacted bird migration between 1999–2017 by looking at within-season changes of bird distributions related to hurricanes Bret (1999), Rita (2005), Katrina (2005), and Harvey (2017). To assess the impact of each hurricane on stopover distributions during autumn, we compared vertically integrated reflectivity (VIR), a measure of bird stopover biomass at the ground derived from weather surveillance radars, after each hurricane to a baseline VIR averaged across the preceding three years. After modeling VIR with land cover and climate variables, the common important variables across the four hurricanes included temporal period after the storm, latitude, longitude, and distance to the hurricane. While we found proportionally more birds closer to the path of the hurricane, likely due to birds generally concentrating along the coast, our standardized differences suggest that more birds were detected farther away from the hurricane. For most hurricanes, we estimated more birds during the middle temporal period after the storm compared to the initial or last periods. Despite hurricanes being unpredictable and unique, our results improve understanding of the impacts hurricanes can have on migratory birds.


Simultaneous near-range detection of migrating birds with NEXRAD radar and moonwatching

Eli S Bridge; Valery Melnikov

Level II data from the NEXRAD weather radar network are widely used to study migrating birds in North America. However, these data products exclude a radius of a few km around each radar, and it is unclear whether reflectivity from within this radius is useful for detecting flying animals. We used a WSR-88D radar (KOUN in Norman, OK) in conjunction with an automated moonwatching device to simultaneously collect visual footage and reflectivity data from migrating birds at distances of less than 5 km. The observation angles of the two devices were matched so that they monitored the same portion of the night sky, and we recorded level I data from the radar within range gates from 250 m to 5000 m. Birds detected visually were clearly manifested in the radar reflectivity products, which included velocity and ranging information. This work points to the potential of creating a new type of bird observatory at each of the 150+ NEXRAD stations by simply analyzing each stream of ‘level I’ data to extract likely bird detections.

Incorporating radar aeroecology into U.S. State Wildlife Action Plans for migratory bird conservation

Claire E. Nemes; Gwenda L. Brewer; Jeffrey J. Buler; Fengyi Guo; Brian R. Tsuru; Emily B. Cohen

Conservation and management of stopover habitat is critical for the persistence and recovery of migratory bird populations. In the U.S., individual states develop their own State Wildlife Action Plans (SWAPs) to guide conservation and management of wildlife species and critical habitats within their borders. However, SWAPs have historically focused mainly on the breeding season of migratory species rather than habitat requirements during migration. Furthermore, unlike shorebirds that are relatively confined to discrete staging areas, migration of landbirds in North America typically occurs over a broad front, complicating efforts to identify and protect important stopover habitats. Weather surveillance radar can help fill this need, providing invaluable data of overall bird biomass to help identify and prioritize landbird stopover habitats at scales relevant to wildlife management. However, radar may be underutilized in conservation plans if researchers and practitioners do not work together to develop shared objectives and ensure that radar-derived products are accessible, interpretable, and useful to conservation practitioners. To address this disconnect, we brought together academic researchers, state wildlife biologists, and other conservation managers to co-develop plans for incorporating stopover habitat into Maryland’s 2025 SWAP. For this ongoing project, we are mapping spring and fall stopover hotspots across the state using weather radar data. In addition, we are compiling other available information about migrating bird distributions and threat sources to identify where hazards are likely to impact migrants, with a focus on species and regions of management concern in Maryland. Using a co-development approach to incorporate radar-derived information on migratory bird stopover habitat into documents that guide management actions and priorities will improve on-the-ground conservation of migratory landbird communities.

A semi-automated system to detect and track spruce budworm mass dispersal flights using weather radar

Jennie L. Pearce

Spruce Budworm (SBW) is a native moth defoliator of North American conifer forests, with balsam fir Abies balsamea and white spruce Picea glauca being the primary host plants. Trees usually die after four or five consecutive years of severe defoliation, and outbreaks can result in the defoliation of tens of millions of hectares of trees over several years. The key to mitigating impact on timber supply is the early detection of spruce budworm spread from high density to low density areas during an outbreak. Of particular importance are long-distance, mass exodus flights that can initiate new epicenters, contributing to the rapid spread of large-scale SBW outbreaks. The number of dispersal events during a flight season are limited and difficult to track because the triggers for take-off are unknown, and the trajectories are stochastic (wind-related). In an earlier study, Boulanger et al. (2017) confirmed that SBW mass exodus dispersal events could be detected by weather surveillance radar. Using historical monitoring data from an active SBW outbreak in Quebec, Canada and weather surveillance radar from nearby Canadian stations, we explore the feasibility of using weather surveillance radar to automate the detection, characterization, tracking and visualization of SBW mass exodus flights. Our ultimate goal is to develop a web-based, real-time tracking tool that will document SBW mass exodus flights within weather surveillance radar.

Seeking scale-dependent drivers of species-specific filtering from passage in migratory birds

Brian R. Tsuru; Jeffrey J. Buler; Joely G. DeSimone; Claire Nemes; Emily B. Cohen

Many bird species make long-distance migratory journeys across the globe every year. Most nocturnal migrants spend more time on the ground resting and refueling (termed stopover) than in migratory flight. When and where migrating birds decide to stop flying and “filter” out of the airspace to terrestrial stopover sites likely depends on a host of hierarchical and scale-dependent factors, both intrinsic and extrinsic. Previous work has identified some of the weather conditions and landscape features that are associated with high densities of birds on stopover (e.g., disadvantageous headwinds, abundant forest cover), and recent work suggests that migrations are also influenced by social relationships among co-migrating birds. However, little is known about how weather and terrestrial habitat interact with individual physiological condition and social relationships to filter birds out of passage flight, or how species may respond differently to these filters. Even less is known about the scales at which the drivers of filtering are most meaningful, which may also differ among species. We plan to study these filters by combining species-agnostic weather surveillance radar data, used to estimate passage rates and stopover densities of avian migrants, with species-specific data from several long-term bird banding stations, used to estimate the diversity and abundance of species on stopover. We will also incorporate remotely sensed data on atmospheric conditions and terrestrial habitat features, assessed across a range of spatiotemporal scales. In this new project, we are exploring approaches (e.g., stopover-to-passage ratio, fluid dynamics modeling) that can help discern whether, how, and at what scales different species respond to the same putative filters. Our objective is to address the species-specific drivers of filtering from the airspace to stopover at inland and coastal sites, and their role in establishing biotic interactions between co-migrants during stopover.

Environmental factors affecting radar detected departures and landings of migrating birds

Yuval Werber; Nir Sapir

Long distance migration involves real-time decision-making processes, without which organisms would be unable to reach their destination. Migrants traversing changing landscapes and weather conditions must constantly balance the urgency to arrive with delicate energy management by avoiding conditions in which migration is too costly. Flying migrants are exposed to varying weather conditions which dramatically affect the transport cost of flight. Weather can aid or hinder migration efforts, and aerial migrants are constantly faced with a choice: to fly or to stop. The decision to depart for flight integrates internal and external factors that result in specific take-off time. Similarly, the decision to stop flying also involves the integration of factors that result in a specific landing time. We utilized vertical-looking radar data to calculate individual ascent rates and explored how they are affected by meteorological conditions, opening a hatch to these complex, crucial decision-making processes. Our direct approach to document landing and departure offers a unique opportunity to study the factors affecting them in space and time. We developed a pipeline to calculate bird ascent and applied it to migrating passerines in the Hula Valley, a central stop-over site on a globally-important flyway in the Eurasian-Afrotropical migration system. Our analysis confirms expected departure and landing patterns of nocturnal migrants throughout the night and reveals that crosswinds constitute a main factor affecting take-off and landing decision in passerine migration in the region. Passerines avoid drifting towards the Mediterranean Sea by landing, and prefer to take off when winds are blowing away from the sea. Our findings represent a hitherto undescribed pattern of migration initiation and termination, with implications for migration scheduling of flight and stopover periods, as well as bird mortality due to harmful anthropogenic structures in the airspace.

Lets be more specific: Integrating species level insight into large scale radar aeroecology research

Yuval Werber

Radar’s inability to resolve taxonomic affiliation is a major limitation for the field of radar aeroecology. However, as the number of species in an environment at any moment is finite, one can taxonomically describe radar observed phenomena finitely. We propose a preferable workflow compared to the dismissal the subject receives, to complement radar studies, connect radar output to taxonomic reality based on factual data and a robust logic, and form a basis for radar driven, taxon specific conclusions. First, external information about regional phenology and species ecology can be used to create species lists containing all species potentially detected in the study. Next, informative radar parameters can be used to further refine taxonomic estimations so that the taxonomic structure of detected aerial communities can actually be assessed quite definitively.
We employed this approach in a Birdscan MR1 study of summer passerine activity in the Hula valley, Israel. We chose detections that crossed the center of detection beam (where RCS accurately reflects target size) and grouped them to 1Hz wing flapping groups. The RCS of consecutive groups was compared using Tukey’s HSD procedure, and significant differences were taken as proof that targets were morphologically different and likely represent separate species groups. We used external information to divide all passerine species in the region accordingly, and kept phenologically relevant species for each month. This resulted in a database of potential species for each passerine detection throughout the year, with the smallest group (July passerines, >20 HZ) consisting of only three species, one much more common than the others. We believe that incorporating taxonomic insight as standard practice in radar aeroecology is likely to uncover hidden discoveries and novel research directions, and recommend publishing “reference species lists” as supplementary material for radar publications.