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From Agricultural Benefits to Aviation Safety: Realizing the Potential of Continent-Wide Radar Networks

From Agricultural Benefits to Aviation Safety: Realizing the Potential of Continent-Wide Radar... Forum From Agricultural Benefits to Aviation Safety: Realizing the Potential of Continent-Wide Radar Networks SILKE BAUER, JASON W. CHAPMAN, DON R. REYNOLDS, JOSÉ A. ALVES, ADRIAAN M. DOKTER, MYLES M. H. MENZ, NIR SAPIR, MICHAŁ CIACH, LARS B. PETTERSSON, JEFFREY F. KELLY, HIDDE LEIJNSE, AND JUDY SHAMOUN-BARANES Migratory animals provide a multitude of services and disservices—with benefits or costs in the order of billions of dollars annually. Monitoring, quantifying, and forecasting migrations across continents could assist diverse stakeholders in utilizing migrant services, reducing disservices, or mitigating human–wildlife conflicts. Radars are powerful tools for such monitoring as they can assess directional intensities, such as migration traffic rates, and biomass transported. Currently, however, most radar applications are local or small scale and therefore substantially limited in their ability to address large-scale phenomena. As weather radars are organized into continent-wide networks and also detect “biological targets,” they could routinely monitor aerial migrations over the relevant spatial scales and over the timescales required for detecting responses to environmental perturbations. To tap these unexploited resources, a concerted effort is needed among diverse fields of expertise and among stakeholders to recognize the value of the existing infrastructure and data beyond weather forecasting. AQ1 t is increasingly recognized that migrating organisms  Shamoun-Baranes et  al. 2014) and the recognition of the Ihave ecological effects on resident communities and eco- airspace as habitat that may also need conservation (Diehl systems (Bauer and Hoye 2014), and these can represent 2013, Lambertucci 2014). a multitude of services and disservices that are relevant to A variety of radar systems exists, from specialized human infrastructure, agriculture, and welfare. Services bird- or insect-detecting radars to meteorological radars. provided by migrant animals include economic benefits in Although the latter are primarily designed to detect pre- the order of billions of dollars annually (Boyles et al. 2011); cipitation, they can also detect a wide range of “biological likewise, their disservices and human–wildlife conflicts (e.g., targets.” Meteorological radar has mostly been used in bird–aircraft collisions) produce significant costs, both eco- ornithological research (a) to quantify aerial biomass nomically, and in terms of human and animal lives (Allan fluxes of birds, as well as flight speeds and directions and Orosz 2001, Marra et  al. 2009). If we want to make across altitude profiles and over time (e.g., Dokter et  al. better use of the services migratory animals provide, reduce 2011, Farnsworth et  al. 2016); (b) to quantify migratory their disservices, and mitigate human–wildlife conflicts, stopovers from low-elevation scans at the moment of we require large-scale and long-term monitoring tools for synchronized mass departures around sunset (Buler and quantifying and, ultimately, forecasting migrations across Dawson 2014); and (c) to detect locations and emergence continents (Kelly and Horton 2016). behaviors at localized roosts (e.g., Bridge et  al. 2016). Among the various existing methods, radars are excellent Recent upgrades of meteorological radars to dual polar- tools for monitoring mass movements of aerial organisms. ization have improved the distinction between meteoro- They have been used in ecological research for decades logical and biological targets, between various taxa aloft (e.g., Gauthreaux and Belser 2003) but have recently under- (Stepanian et  al. 2016), as well as their body alignments gone a renaissance with the emergence of aeroecology (Horton et  al. 2016). Meteorological radar observations as a di stinct research field (Chilson et  al. 2012a, 2012b, of bats have so far remained limited to mass foraging BioScience 67: 912–918. © The Author(s) 2017. Published by Oxford University Press on behalf of the American Institute of Biological Sciences. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com doi:10.1093/biosci/bix074 Advance Access publication 28 June 2017 912 BioScience • October 2017 / Vol. 67 No. 10 https://academic.oup.com/bioscience Forum flights from roosts (Horn and Kunz 2007, Krauel et  al. (Bauer and Hoye 2014, Hu et al. 2016). The sheer presence of 2015). Interestingly, mass movements of small insects migrants may create human–wildlife conflicts; their trans- also show prominently in meteorological radar data, and port and trophic effects may be essential and economically their movements typically dominate meteorological radar beneficial but can also pose health risks or inflict damage. returns during daytime (Nieminen et al. 2000, Drake and Examples of the multitude of highly desirable services Reynolds 2012). Insects have the potential to provide trac- include Brazilian free-tailed bats (Tadarida braziliensis), ers of wind in “clear-air” (nonprecipitation) conditions, which consume large quantities of migrant moths, such as but insect movements with a directed body orientation can corn earworm (Helicoverpa zea), one of the most important be observed over large geographic areas (Rennie 2014), agricultural pests in North America (Boyles et  al. 2011). and the observed velocities may not be representative of Migratory bats have also long been acknowledged for their the wind flow. pollination services (of, e.g., columnar cacti and agave), Because meteorological radars are organized in conti- which play vitally important roles in the plants’ fruit pro- nent-wide networks within a permanent and continuously duction (Fleming and Valiente-Banuet 2002, Kunz et  al. operational infrastructure, they can provide standardized 2011). Similarly, migratory birds can enhance the dispersal long-term and large-scale monitoring and quantification of of plant seeds or small invertebrates and therefore increase aerial migrants, in addition to their meteorological products. the genetic exchange between (fragmented) populations and Using such networks for following aerial migrants would potentially assist with ecosystem recovery (van Leeuwen exceed the spatial and temporal coverage of current methods et  al. 2012, Viana et  al. 2016). Among other ecosystem by orders of magnitude and provide essential information services, migratory bogong moths (Agrotis infusa) are an for groundbreaking and complementary applications, as important food source for wildlife and aboriginal people in well as answer important long-standing and novel questions Australia (Green 2011). Although the overall economic ben- in migration ecology and beyond (Kelly and Horton 2016). efit of these services is difficult to estimate, the value of, for As we will detail in the following, the products of radar example, Brazilian free-tailed bats to the agricultural industry networks are, or could be, relevant to a diverse array of in terms of crop damage avoided and reduction in pesticide stakeholders, including airport and windfarm operators, use amounts to billions of dollars per year (Boyles et al. 2011). agricultural managers and farmers, public-health agencies, In contrast to these services, migrants can also directly policymakers, and conservation practitioners (figure 1). inflict harm or damage, either by feeding on crops or by However, as yet, the potential of existing radar networks affecting important ecosystem functions. For instance, a has remained largely untapped for diverse reasons: First, the square-kilometer-sized swarm of locusts (e.g., Schistocerca societal benefits of the existing radar infrastructure beyond gregaria) contains about 40 million individuals that will eat meteorological purposes are not broadly recognized. Second, the same amount of food per day as about 35,000 people no standards have been established for quality, sharing, and (www.fao.org/ag/locusts/en/info/info/faq). Similarly, many archiving of “biological” radar data. Furthermore, meteo- migratory goose populations have thrived over the past rological radar operators tend to be focused on providing decades, and their foraging is increasingly causing conflicts “clean” meteorological radar scans for aviation and short- with agriculture and raising concern for the functioning of term weather forecasting, often regarding biological signals their Arctic breeding grounds as a global carbon sink (Van as contamination to be removed instead of as a valuable Der Wal et al. 2007). data product. Finally, many operational applications such Another harmful effect of migrants is their role in the as early-warning systems for agriculture, flight safety, or the long-distance transport of parasites and pathogens of plants, spread of vector-borne diseases remain to be developed. animals, and humans (e.g., Reynolds et al. 2006, Altizer et al. Therefore, we aim here at raising the awareness of stake- 2011, Dao et  al. 2014, Chapman et  al. 2015): Many insects holders (and of society as a whole) to the benefits of using not only are agricultural pest species per se but also vector a radar networks for monitoring aerial migrations. To this end, variety of plant viruses (e.g., Rhopalosiphum padi aphids vec- we outline the services and disservices of aerial migrants for tor barley yellow dwarf virus). Also, bats may carry agents human well-being and ecosystem functioning and provide of serious human diseases (e.g., the recent Ebola outbreak examples of how radars are currently used to monitor aerial in Western Africa originated from migratory straw-colored movements. Furthermore, we highlight the challenges that fruit bats, Eidolon helvum; Peel et  al. 2013). And finally, need to be addressed regarding future extensions, which migratory birds have regularly been blamed for spreading require joint efforts by meteorologists and ecologists, radar pathogens such as avian influenza virus, West Nile virus, or and signal-processing engineers, and information scientists. other disease vectors (e.g., Tian et al. 2015). The often-immense numbers of migrants may create seri- Services and disservices of aerial migrants ous human–wildlife conflicts: For instance, the annual costs Migrations involve immense numbers of individuals and of bird collisions with aircraft are up to $1.2 billion world- constitute massive shifts of biomass that influence com- wide (Allan and Orosz 2001)—a widely publicized example munities and ecosystems through the transport of nutrients, being US Airways flight 1549, which made an emergency energy, or other organisms and through trophic interactions landing on the Hudson River after colliding with a flock https://academic.oup.com/bioscience October 2017 / Vol. 67 No. 10 • BioScience 913 Forum Figure 1. A variety of stakeholders can benefit from better using the services of aerial migrants, reducing their disservices and mitigating human–wildlife conflicts—a few of which are exemplarily depicted in the outer images. Photos and graphics (clockwise from top): (a) Flock of birds surrounding an airplane, copyright Konwicki Marcin (shutterstock. com). (b) Bird watchers during Batumi Raptor Count in Georgia, copyright Albert de Jong. (c) Visualization of bird migration data as identified from weather radars in Belgium and The Netherlands, modified from Shamoun-Baranes and colleagues (2016). (d) Veterinarians taking preventive measures to contain spread of avian influenza, copyright Irina Gor (shutterstock.com). (e) Lesser long-nosed bat (Leptonycteris yerbabuenae) pollinating a saguaro cactus, copyright Merlin Tuttle. (f ) Locust swarm, copyright aaabbbccc (shutterstock.com). (g) Brazilian free-tailed bat (Tadarida brasiliensis) catching a moth, copyright Merlin Tuttle. (h) Distribution of Natura 2000 sites in the European Union (2014), copyright European Environment Agency (EEA). (i) Flock of foraging barnacle geese (Branta leucopsis) copyright Hugh Jansman. (j) Geese passing wind turbines, copyright roundstripe (shutterstock.com). of geese (Marra et  al. 2009). Collisions with manmade information: Where are migrants going, when, and how structures such as power lines, wind turbines, or towers can many? These are fundamental questions in migration ecol- disrupt their normal functioning and kill large numbers of ogy for which radar methods are particularly useful as they birds and bats annually, but there is great variation in esti- can assess directional intensities, such as fluxes and migra- mates of costs, fatalities, and their ecological significance tion traffic rates (Drake and Reynolds 2012), and/or biomass (Cryan et al. 2014). transported along migration pathways (Hu et al. 2016). Small-scale, local radars are used at airports worldwide The potential of continent-wide radar networks to enhance aviation safety by monitoring bird movements A prerequisite for managing the effects of migrants on in near real time (Gauthreaux and Schmidt 2013). For ecosystems and their interactions with humans is basic instance, in the United States, the Netherlands, and Belgium, 914 BioScience • October 2017 / Vol. 67 No. 10 https://academic.oup.com/bioscience Forum operational weather radars are used for warnings that changes in spatial distribution and timing of aerial migra- inform ground-based bird control units of potential threats tions in response to environmental perturbations such as or that lead to changes in aircraft takeoffs and landings in large-scale habitat alterations or long-term climatic changes. order to reduce the risk of bird strikes (see, e.g., www.flysafe- Basic data on key migration routes and stopover sites pro- birdtam.eu; Shamoun-Baranes et  al. 2008). Some countries vided by radar monitoring can be used to prioritize conser- have also developed predictive (i.e., forecast) models from vation efforts (Gauthreaux and Belser 2003) and support the radar monitoring, which provide advanced warnings of establishment of aerial protected areas (Diehl 2013). potential risks from birds (Van Belle et  al. 2007). However, Furthermore, weather-radar networks would also provide such forecasts are still rare because robust predictive models the long-term data sets of broader spatial scope needed to can only be developed with data collected over several years develop robust (forecast) models and improve early-warning at specific areas, and they need to convert bird densities to systems such that actions can be initiated before migrants warnings that can easily be interpreted by air-traffic control- actually arrive in an area of interest. Although still largely lers, flight planners, and pilots. speculative, these networks could identify the pathways used Similarly, collision risk at wind turbines could be severely by potential disease vectors, which may assist national health reduced with radar-based shutdowns on demand—that is, agencies in containing zoonotic diseases and prevent out- when radar monitoring is installed in regions with high breaks by the early application of control measures—similar numbers of wind turbines and the detection of high num- to the timely application of control measures that currently bers of birds passing through will automatically interrupt reduces the spread of insect agricultural pests into surround- operation (Marques et al. 2014). ing areas and controls massive infestations (e.g., Drake and Special-purpose entomological radars have been used Wang 2013). for more than 40 years in applied research on the migra- Thus, standardized large-scale and long-term monitoring tion of insect pests (Drake and Reynolds 2012). These will not only lead to an improved understanding of animal include investigations on pests such as African army- migrations but could also ultimately support key areas of worm (Spodoptera exempta) and cotton bollworm moths industry, such as agriculture and the (wind) energy indus- (Helicoverpa armigera), rice planthoppers, Australian plague try, as well as facilitate the implementation of preventative locusts (Chortoicetes terminifera), and aphids (Drake and measures to mitigate human–wildlife conflicts, and thereby Reynolds 2012), but there have been rather few attempts assist in nature conservation and the planning of protected at operational use. Currently, radar inputs into decision- areas. support systems take two forms: those from dedicated vertical-beam profiling systems and those from operational A roadmap for implementing continent-wide radar networks of weather-surveillance radars. An example of the networks first is the monitoring and forecasting of Australian plague Continental radar networks already exist for meteorological locust (Chortoicetes terminifera), which rely on the inputs data and products, such as the Operational Programme for from autonomously operating insect-monitoring radars the Exchange of Weather Radar Information (OPERA net- that detect major nocturnal movements (Drake and Wang work) in Europe (Huuskonen et al. 2014). In addition, Next 2013). Examples for the second are early warnings of pest Generation Radar (NEXRAD) is used in the United States, insects invading cropping regions, which rely on meteoro- and large radar networks are also operational in Russia logical and research radars integrated with trap catches and and China. Adapting these to monitor aerial migrations as atmospheric dispersion modeling. Prominent among these recently initiated in Europe through the European Network are the warnings of mass immigrations of bird cherry aphids for the Radar Surveillance of Animal Movement (www. (Rhopalosiphum padi) and diamondback moths (Plutella enram.eu; Shamoun-Baranes et  al. 2014) and in the United xylostella) into southern Finland (Leskinen et  al. 2011) States (Kelly et  al. 2016) would yield extraordinary added or corn earworm moths into the southern United States value and provide answers to the problems raised above. (Westbrook et  al. 2014), which have been identified from This would be a cost-effective solution for establishing long- weather-radar outputs. term and near-real-time ecological monitoring and early- Thus, there are already many (economically) important warning networks. However, although several milestones applications of radar monitoring; however, most of these are have been reached, there are a number of challenges that local or small scale and target only a subset of the problems need to be addressed before we can tap these resources (see raised above. We could greatly benefit if we would extend table 1 and points 1–5 below). Several of these challenges are them to the spatial scales relevant to migratory movements, probably common to all radar networks but there are also to the longer timescales required for detecting responses to some specific differences. For instance, a major obstacle in anthropogenic or environmental changes, and to other novel Europe is the diversity in national weather radars in terms applications. Once such monitoring has become standard, of radar types, settings during operation, and quality of long-term archives of aerial migrations would provide more data for biological purposes, as well as rules, regulations, complementary and comprehensive data than small-scale and national cost models that may limit access to, and the scattered studies and set an important baseline for detecting exchange of, data. https://academic.oup.com/bioscience October 2017 / Vol. 67 No. 10 • BioScience 915 Forum Table 1. Recent milestones and remaining challenges in implementing continent-wide networks of weather radars. Topic Recent milestones Remaining challenges Radar data collection, Radar data collection and • Standardization of meteorological data • Create European archive and harmonize exchange, and exchange formats national historical archives infrastructure • Setup of radar data centers, such as • Harmonize scanning schemes between ODYSSEY (OPERA data center) and countries NOAA’s national centers for environmental • Provide open access to data information (NCEI) • Exchange of complete raw radar data Radar hardware and • Upgrades of weather radars to dual • Conform radar settings between countries settings polarization • Improve low-altitude (less than 100 meters) coverage • Apply meteorological filters only after retrieval of biological signals Big-data information • Algorithms for extraction of biological • Install (cloud-)computing infrastructure for technology signals integrated into meteorological processing radar data data center in Europe • Setup data portal for biological radar • NEXRAD data on Amazon Web Services products From radar data to Classification of biological • Automated algorithms for • Develop algorithms for biological information targets, ground-truthing, – generating vertical profiles for broad- – accurate removal of precipitation and validation front migration – identification of insects and bird–insect – distinction of rain-, insect- and bird- mixtures dominated cases – quantification of flocking and soaring – peak-emergence flights bird migration • Body shape and alignment from dual- • Cross-validate radar types in as-yet polarimetric data underrepresented regions • Cross-validation between bird, insect, and weather radars in some regions Integration of data • Correction methods for bias with distance • Close gaps between individual radars from multiple sources, from radar • Merge scans of different radars visualization • Visualizations based on vertical profiles • Combine data of multiple radars into for data exploration and outreach contiguous velocity–density fields • Integrate radar data with complementary data on, for example, habitat use, land cover, ringing, individual tracking, etc. Operational services • Regional flight safety model • Develop continent-wide flight safety • Pest insect warning systems models • Develop warning systems for migration of disease vectors The most important common challenges are probably and organizational differences need to be harmonized and to raise the awareness of public agencies, radar operators, should preferably be embedded in open-data policies. and stakeholders of the value of radar networks beyond meteorology; to install additional data infrastructure and Data infrastructure. Access to radar data is often the prime implement efficient classification algorithms; and to develop practical bottleneck for biological applications. Therefore, operational services for existing and novel applications, we need investments in infrastructure for data archiving and possibly complementing weather-radar data with other data efficient access to data, in computational power for process- (table 1). ing and analyzing the voluminous data, and in personnel for creating reliable, reproducible, and real-time radar products. Radar data collection and exchange. Although great progress Ideally, data would be archived in publicly accessible cloud has been made in harmonizing and exchanging meteorolog- storage, similar to the NEXRAD archive in the United States. ical data at national and international levels in Europe (e.g., These actions should lead to a well-designed and docu- by the EUMETNET OPERA program; Huuskonen et  al. mented data infrastructure and workflow to support collab- 2014), this still features high on the task list for biological orative research and the development of sustainable services. data. Currently, many countries do not store and exchange the complete basic weather-radar data needed to extract Toolbox of classification algorithms. Improving the distinction biological information (polar volume data, also referred between biological and nonbiological targets in weather- to as level-2 data in the United States). Furthermore, data radar data will also benefit meteorologists because biologi- quality substantially differs between countries, and radar cal targets frequently contaminate meteorological data, and settings may not always yield high-quality biological data, clearly (or more comprehensively) excluding “bioscatter” such as when filter settings are too exclusive for the weak will improve meteorological products (Rennie et  al. 2015). (but highly detectable) biological signals or when biologi- However, the classification of biological targets also needs cal signals are removed before data are stored. Finally, data improvement; this can be achieved in part through cross- policies that often vary between countries due to political calibration efforts using different sensors under a broad 916 BioScience • October 2017 / Vol. 67 No. 10 https://academic.oup.com/bioscience Forum range of environmental conditions and across geographic Animal Movement (ENRAM), in facilitating this collabo- regions (Dokter et al. 2011). Furthermore, dual-polarization ration. JFK’s contribution was supported by NSF grant no. radar has great potential for improving target classifica- DGE-1545261. tion (Stepanian et  al. 2016). Finally, robust algorithms for extracting animal migration parameters should be imple- References cited mented into a basic “toolbox” that runs on all weather radars Allan JR, Orosz AP. 2001. The costs of birdstrikes to commercial aviation. in a network. Pages 217–226 in Bird Strike Committee–USA/Canada. Bird Strike Committee Proceedings. University of Nebraska. 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International Aveiro, Campus de Santiago, in Portugal, and with the South Iceland Journal of Biometeorology 44: 172–181. Research Centre at the University of Iceland, in Selfoss. Adriaan M. Peel AJ, et  al. 2013. Continent-wide panmixia of an African fruit bat Dokter and Judy Shamoun-Baranes are affiliated with the Institute for facilitates transmission of potentially zoonotic viruses. Nature Biodiversity and Ecosystem Dynamics at the University of Amsterdam, in Communications 4 (art. 2770). The Netherlands. AMD is also affiliated with the Lab of Ornithology at Rennie SJ. 2014. Common orientation and layering of migrating insects Cornell University, in Ithaca, New York. Myles M. H. Menz is affiliated in southeastern Australia observed with a Doppler weather radar. with the Institute of Ecology and Evolution at the University of Bern, in Meteorological Applications 21: 218–229. Switzerland, and with the School of Biological Sciences at the University Rennie SJ, et  al. 2015. Bayesian echo classification for Australian single- of Western Australia, in Crawley. Nir Sapir is with the Department of polarization weather radar with application to assimilation of radial Evolutionary and Environmental Biology at the University of Haifa, in velocity observations. Journal of Atmospheric and Oceanic Technology Israel. Michał Ciach is affiliated with the Department of Forest Biodiversity 32: 1341–1355. at the University of Agriculture, in Krakow, Poland. Lars B. Pettersson is Reynolds DR, Chapman JW, Harrington R. 2006. The migration of insect with the Biodiversity Unit, Department of Biology, at the University of vectors of plant and animal viruses. Advances in Virus Research Lund, in Sweden. Jeffrey F. Kelly is affiliated with the Oklahoma Biological 67: 453–517. Survey and the Department of Biology at the University of Oklahoma, Shamoun-Baranes J, Bouten W, Buurma L, DeFusco R, Dekker A, Sierdsema in Norman. Hidde Leijnse is with the Royal Netherlands Meteorological H, Sluiter F, van Belle J, van Gasteren H, van Loon E. 2008. Avian Institute, in De Bilt, The Netherlands. 918 BioScience • October 2017 / Vol. 67 No. 10 https://academic.oup.com/bioscience http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Bioscience Pubmed Central

From Agricultural Benefits to Aviation Safety: Realizing the Potential of Continent-Wide Radar Networks

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Forum From Agricultural Benefits to Aviation Safety: Realizing the Potential of Continent-Wide Radar Networks SILKE BAUER, JASON W. CHAPMAN, DON R. REYNOLDS, JOSÉ A. ALVES, ADRIAAN M. DOKTER, MYLES M. H. MENZ, NIR SAPIR, MICHAŁ CIACH, LARS B. PETTERSSON, JEFFREY F. KELLY, HIDDE LEIJNSE, AND JUDY SHAMOUN-BARANES Migratory animals provide a multitude of services and disservices—with benefits or costs in the order of billions of dollars annually. Monitoring, quantifying, and forecasting migrations across continents could assist diverse stakeholders in utilizing migrant services, reducing disservices, or mitigating human–wildlife conflicts. Radars are powerful tools for such monitoring as they can assess directional intensities, such as migration traffic rates, and biomass transported. Currently, however, most radar applications are local or small scale and therefore substantially limited in their ability to address large-scale phenomena. As weather radars are organized into continent-wide networks and also detect “biological targets,” they could routinely monitor aerial migrations over the relevant spatial scales and over the timescales required for detecting responses to environmental perturbations. To tap these unexploited resources, a concerted effort is needed among diverse fields of expertise and among stakeholders to recognize the value of the existing infrastructure and data beyond weather forecasting. AQ1 t is increasingly recognized that migrating organisms  Shamoun-Baranes et  al. 2014) and the recognition of the Ihave ecological effects on resident communities and eco- airspace as habitat that may also need conservation (Diehl systems (Bauer and Hoye 2014), and these can represent 2013, Lambertucci 2014). a multitude of services and disservices that are relevant to A variety of radar systems exists, from specialized human infrastructure, agriculture, and welfare. Services bird- or insect-detecting radars to meteorological radars. provided by migrant animals include economic benefits in Although the latter are primarily designed to detect pre- the order of billions of dollars annually (Boyles et al. 2011); cipitation, they can also detect a wide range of “biological likewise, their disservices and human–wildlife conflicts (e.g., targets.” Meteorological radar has mostly been used in bird–aircraft collisions) produce significant costs, both eco- ornithological research (a) to quantify aerial biomass nomically, and in terms of human and animal lives (Allan fluxes of birds, as well as flight speeds and directions and Orosz 2001, Marra et  al. 2009). If we want to make across altitude profiles and over time (e.g., Dokter et  al. better use of the services migratory animals provide, reduce 2011, Farnsworth et  al. 2016); (b) to quantify migratory their disservices, and mitigate human–wildlife conflicts, stopovers from low-elevation scans at the moment of we require large-scale and long-term monitoring tools for synchronized mass departures around sunset (Buler and quantifying and, ultimately, forecasting migrations across Dawson 2014); and (c) to detect locations and emergence continents (Kelly and Horton 2016). behaviors at localized roosts (e.g., Bridge et  al. 2016). Among the various existing methods, radars are excellent Recent upgrades of meteorological radars to dual polar- tools for monitoring mass movements of aerial organisms. ization have improved the distinction between meteoro- They have been used in ecological research for decades logical and biological targets, between various taxa aloft (e.g., Gauthreaux and Belser 2003) but have recently under- (Stepanian et  al. 2016), as well as their body alignments gone a renaissance with the emergence of aeroecology (Horton et  al. 2016). Meteorological radar observations as a di stinct research field (Chilson et  al. 2012a, 2012b, of bats have so far remained limited to mass foraging BioScience 67: 912–918. © The Author(s) 2017. Published by Oxford University Press on behalf of the American Institute of Biological Sciences. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com doi:10.1093/biosci/bix074 Advance Access publication 28 June 2017 912 BioScience • October 2017 / Vol. 67 No. 10 https://academic.oup.com/bioscience Forum flights from roosts (Horn and Kunz 2007, Krauel et  al. (Bauer and Hoye 2014, Hu et al. 2016). The sheer presence of 2015). Interestingly, mass movements of small insects migrants may create human–wildlife conflicts; their trans- also show prominently in meteorological radar data, and port and trophic effects may be essential and economically their movements typically dominate meteorological radar beneficial but can also pose health risks or inflict damage. returns during daytime (Nieminen et al. 2000, Drake and Examples of the multitude of highly desirable services Reynolds 2012). Insects have the potential to provide trac- include Brazilian free-tailed bats (Tadarida braziliensis), ers of wind in “clear-air” (nonprecipitation) conditions, which consume large quantities of migrant moths, such as but insect movements with a directed body orientation can corn earworm (Helicoverpa zea), one of the most important be observed over large geographic areas (Rennie 2014), agricultural pests in North America (Boyles et  al. 2011). and the observed velocities may not be representative of Migratory bats have also long been acknowledged for their the wind flow. pollination services (of, e.g., columnar cacti and agave), Because meteorological radars are organized in conti- which play vitally important roles in the plants’ fruit pro- nent-wide networks within a permanent and continuously duction (Fleming and Valiente-Banuet 2002, Kunz et  al. operational infrastructure, they can provide standardized 2011). Similarly, migratory birds can enhance the dispersal long-term and large-scale monitoring and quantification of of plant seeds or small invertebrates and therefore increase aerial migrants, in addition to their meteorological products. the genetic exchange between (fragmented) populations and Using such networks for following aerial migrants would potentially assist with ecosystem recovery (van Leeuwen exceed the spatial and temporal coverage of current methods et  al. 2012, Viana et  al. 2016). Among other ecosystem by orders of magnitude and provide essential information services, migratory bogong moths (Agrotis infusa) are an for groundbreaking and complementary applications, as important food source for wildlife and aboriginal people in well as answer important long-standing and novel questions Australia (Green 2011). Although the overall economic ben- in migration ecology and beyond (Kelly and Horton 2016). efit of these services is difficult to estimate, the value of, for As we will detail in the following, the products of radar example, Brazilian free-tailed bats to the agricultural industry networks are, or could be, relevant to a diverse array of in terms of crop damage avoided and reduction in pesticide stakeholders, including airport and windfarm operators, use amounts to billions of dollars per year (Boyles et al. 2011). agricultural managers and farmers, public-health agencies, In contrast to these services, migrants can also directly policymakers, and conservation practitioners (figure 1). inflict harm or damage, either by feeding on crops or by However, as yet, the potential of existing radar networks affecting important ecosystem functions. For instance, a has remained largely untapped for diverse reasons: First, the square-kilometer-sized swarm of locusts (e.g., Schistocerca societal benefits of the existing radar infrastructure beyond gregaria) contains about 40 million individuals that will eat meteorological purposes are not broadly recognized. Second, the same amount of food per day as about 35,000 people no standards have been established for quality, sharing, and (www.fao.org/ag/locusts/en/info/info/faq). Similarly, many archiving of “biological” radar data. Furthermore, meteo- migratory goose populations have thrived over the past rological radar operators tend to be focused on providing decades, and their foraging is increasingly causing conflicts “clean” meteorological radar scans for aviation and short- with agriculture and raising concern for the functioning of term weather forecasting, often regarding biological signals their Arctic breeding grounds as a global carbon sink (Van as contamination to be removed instead of as a valuable Der Wal et al. 2007). data product. Finally, many operational applications such Another harmful effect of migrants is their role in the as early-warning systems for agriculture, flight safety, or the long-distance transport of parasites and pathogens of plants, spread of vector-borne diseases remain to be developed. animals, and humans (e.g., Reynolds et al. 2006, Altizer et al. Therefore, we aim here at raising the awareness of stake- 2011, Dao et  al. 2014, Chapman et  al. 2015): Many insects holders (and of society as a whole) to the benefits of using not only are agricultural pest species per se but also vector a radar networks for monitoring aerial migrations. To this end, variety of plant viruses (e.g., Rhopalosiphum padi aphids vec- we outline the services and disservices of aerial migrants for tor barley yellow dwarf virus). Also, bats may carry agents human well-being and ecosystem functioning and provide of serious human diseases (e.g., the recent Ebola outbreak examples of how radars are currently used to monitor aerial in Western Africa originated from migratory straw-colored movements. Furthermore, we highlight the challenges that fruit bats, Eidolon helvum; Peel et  al. 2013). And finally, need to be addressed regarding future extensions, which migratory birds have regularly been blamed for spreading require joint efforts by meteorologists and ecologists, radar pathogens such as avian influenza virus, West Nile virus, or and signal-processing engineers, and information scientists. other disease vectors (e.g., Tian et al. 2015). The often-immense numbers of migrants may create seri- Services and disservices of aerial migrants ous human–wildlife conflicts: For instance, the annual costs Migrations involve immense numbers of individuals and of bird collisions with aircraft are up to $1.2 billion world- constitute massive shifts of biomass that influence com- wide (Allan and Orosz 2001)—a widely publicized example munities and ecosystems through the transport of nutrients, being US Airways flight 1549, which made an emergency energy, or other organisms and through trophic interactions landing on the Hudson River after colliding with a flock https://academic.oup.com/bioscience October 2017 / Vol. 67 No. 10 • BioScience 913 Forum Figure 1. A variety of stakeholders can benefit from better using the services of aerial migrants, reducing their disservices and mitigating human–wildlife conflicts—a few of which are exemplarily depicted in the outer images. Photos and graphics (clockwise from top): (a) Flock of birds surrounding an airplane, copyright Konwicki Marcin (shutterstock. com). (b) Bird watchers during Batumi Raptor Count in Georgia, copyright Albert de Jong. (c) Visualization of bird migration data as identified from weather radars in Belgium and The Netherlands, modified from Shamoun-Baranes and colleagues (2016). (d) Veterinarians taking preventive measures to contain spread of avian influenza, copyright Irina Gor (shutterstock.com). (e) Lesser long-nosed bat (Leptonycteris yerbabuenae) pollinating a saguaro cactus, copyright Merlin Tuttle. (f ) Locust swarm, copyright aaabbbccc (shutterstock.com). (g) Brazilian free-tailed bat (Tadarida brasiliensis) catching a moth, copyright Merlin Tuttle. (h) Distribution of Natura 2000 sites in the European Union (2014), copyright European Environment Agency (EEA). (i) Flock of foraging barnacle geese (Branta leucopsis) copyright Hugh Jansman. (j) Geese passing wind turbines, copyright roundstripe (shutterstock.com). of geese (Marra et  al. 2009). Collisions with manmade information: Where are migrants going, when, and how structures such as power lines, wind turbines, or towers can many? These are fundamental questions in migration ecol- disrupt their normal functioning and kill large numbers of ogy for which radar methods are particularly useful as they birds and bats annually, but there is great variation in esti- can assess directional intensities, such as fluxes and migra- mates of costs, fatalities, and their ecological significance tion traffic rates (Drake and Reynolds 2012), and/or biomass (Cryan et al. 2014). transported along migration pathways (Hu et al. 2016). Small-scale, local radars are used at airports worldwide The potential of continent-wide radar networks to enhance aviation safety by monitoring bird movements A prerequisite for managing the effects of migrants on in near real time (Gauthreaux and Schmidt 2013). For ecosystems and their interactions with humans is basic instance, in the United States, the Netherlands, and Belgium, 914 BioScience • October 2017 / Vol. 67 No. 10 https://academic.oup.com/bioscience Forum operational weather radars are used for warnings that changes in spatial distribution and timing of aerial migra- inform ground-based bird control units of potential threats tions in response to environmental perturbations such as or that lead to changes in aircraft takeoffs and landings in large-scale habitat alterations or long-term climatic changes. order to reduce the risk of bird strikes (see, e.g., www.flysafe- Basic data on key migration routes and stopover sites pro- birdtam.eu; Shamoun-Baranes et  al. 2008). Some countries vided by radar monitoring can be used to prioritize conser- have also developed predictive (i.e., forecast) models from vation efforts (Gauthreaux and Belser 2003) and support the radar monitoring, which provide advanced warnings of establishment of aerial protected areas (Diehl 2013). potential risks from birds (Van Belle et  al. 2007). However, Furthermore, weather-radar networks would also provide such forecasts are still rare because robust predictive models the long-term data sets of broader spatial scope needed to can only be developed with data collected over several years develop robust (forecast) models and improve early-warning at specific areas, and they need to convert bird densities to systems such that actions can be initiated before migrants warnings that can easily be interpreted by air-traffic control- actually arrive in an area of interest. Although still largely lers, flight planners, and pilots. speculative, these networks could identify the pathways used Similarly, collision risk at wind turbines could be severely by potential disease vectors, which may assist national health reduced with radar-based shutdowns on demand—that is, agencies in containing zoonotic diseases and prevent out- when radar monitoring is installed in regions with high breaks by the early application of control measures—similar numbers of wind turbines and the detection of high num- to the timely application of control measures that currently bers of birds passing through will automatically interrupt reduces the spread of insect agricultural pests into surround- operation (Marques et al. 2014). ing areas and controls massive infestations (e.g., Drake and Special-purpose entomological radars have been used Wang 2013). for more than 40 years in applied research on the migra- Thus, standardized large-scale and long-term monitoring tion of insect pests (Drake and Reynolds 2012). These will not only lead to an improved understanding of animal include investigations on pests such as African army- migrations but could also ultimately support key areas of worm (Spodoptera exempta) and cotton bollworm moths industry, such as agriculture and the (wind) energy indus- (Helicoverpa armigera), rice planthoppers, Australian plague try, as well as facilitate the implementation of preventative locusts (Chortoicetes terminifera), and aphids (Drake and measures to mitigate human–wildlife conflicts, and thereby Reynolds 2012), but there have been rather few attempts assist in nature conservation and the planning of protected at operational use. Currently, radar inputs into decision- areas. support systems take two forms: those from dedicated vertical-beam profiling systems and those from operational A roadmap for implementing continent-wide radar networks of weather-surveillance radars. An example of the networks first is the monitoring and forecasting of Australian plague Continental radar networks already exist for meteorological locust (Chortoicetes terminifera), which rely on the inputs data and products, such as the Operational Programme for from autonomously operating insect-monitoring radars the Exchange of Weather Radar Information (OPERA net- that detect major nocturnal movements (Drake and Wang work) in Europe (Huuskonen et al. 2014). In addition, Next 2013). Examples for the second are early warnings of pest Generation Radar (NEXRAD) is used in the United States, insects invading cropping regions, which rely on meteoro- and large radar networks are also operational in Russia logical and research radars integrated with trap catches and and China. Adapting these to monitor aerial migrations as atmospheric dispersion modeling. Prominent among these recently initiated in Europe through the European Network are the warnings of mass immigrations of bird cherry aphids for the Radar Surveillance of Animal Movement (www. (Rhopalosiphum padi) and diamondback moths (Plutella enram.eu; Shamoun-Baranes et  al. 2014) and in the United xylostella) into southern Finland (Leskinen et  al. 2011) States (Kelly et  al. 2016) would yield extraordinary added or corn earworm moths into the southern United States value and provide answers to the problems raised above. (Westbrook et  al. 2014), which have been identified from This would be a cost-effective solution for establishing long- weather-radar outputs. term and near-real-time ecological monitoring and early- Thus, there are already many (economically) important warning networks. However, although several milestones applications of radar monitoring; however, most of these are have been reached, there are a number of challenges that local or small scale and target only a subset of the problems need to be addressed before we can tap these resources (see raised above. We could greatly benefit if we would extend table 1 and points 1–5 below). Several of these challenges are them to the spatial scales relevant to migratory movements, probably common to all radar networks but there are also to the longer timescales required for detecting responses to some specific differences. For instance, a major obstacle in anthropogenic or environmental changes, and to other novel Europe is the diversity in national weather radars in terms applications. Once such monitoring has become standard, of radar types, settings during operation, and quality of long-term archives of aerial migrations would provide more data for biological purposes, as well as rules, regulations, complementary and comprehensive data than small-scale and national cost models that may limit access to, and the scattered studies and set an important baseline for detecting exchange of, data. https://academic.oup.com/bioscience October 2017 / Vol. 67 No. 10 • BioScience 915 Forum Table 1. Recent milestones and remaining challenges in implementing continent-wide networks of weather radars. Topic Recent milestones Remaining challenges Radar data collection, Radar data collection and • Standardization of meteorological data • Create European archive and harmonize exchange, and exchange formats national historical archives infrastructure • Setup of radar data centers, such as • Harmonize scanning schemes between ODYSSEY (OPERA data center) and countries NOAA’s national centers for environmental • Provide open access to data information (NCEI) • Exchange of complete raw radar data Radar hardware and • Upgrades of weather radars to dual • Conform radar settings between countries settings polarization • Improve low-altitude (less than 100 meters) coverage • Apply meteorological filters only after retrieval of biological signals Big-data information • Algorithms for extraction of biological • Install (cloud-)computing infrastructure for technology signals integrated into meteorological processing radar data data center in Europe • Setup data portal for biological radar • NEXRAD data on Amazon Web Services products From radar data to Classification of biological • Automated algorithms for • Develop algorithms for biological information targets, ground-truthing, – generating vertical profiles for broad- – accurate removal of precipitation and validation front migration – identification of insects and bird–insect – distinction of rain-, insect- and bird- mixtures dominated cases – quantification of flocking and soaring – peak-emergence flights bird migration • Body shape and alignment from dual- • Cross-validate radar types in as-yet polarimetric data underrepresented regions • Cross-validation between bird, insect, and weather radars in some regions Integration of data • Correction methods for bias with distance • Close gaps between individual radars from multiple sources, from radar • Merge scans of different radars visualization • Visualizations based on vertical profiles • Combine data of multiple radars into for data exploration and outreach contiguous velocity–density fields • Integrate radar data with complementary data on, for example, habitat use, land cover, ringing, individual tracking, etc. Operational services • Regional flight safety model • Develop continent-wide flight safety • Pest insect warning systems models • Develop warning systems for migration of disease vectors The most important common challenges are probably and organizational differences need to be harmonized and to raise the awareness of public agencies, radar operators, should preferably be embedded in open-data policies. and stakeholders of the value of radar networks beyond meteorology; to install additional data infrastructure and Data infrastructure. Access to radar data is often the prime implement efficient classification algorithms; and to develop practical bottleneck for biological applications. Therefore, operational services for existing and novel applications, we need investments in infrastructure for data archiving and possibly complementing weather-radar data with other data efficient access to data, in computational power for process- (table 1). ing and analyzing the voluminous data, and in personnel for creating reliable, reproducible, and real-time radar products. Radar data collection and exchange. Although great progress Ideally, data would be archived in publicly accessible cloud has been made in harmonizing and exchanging meteorolog- storage, similar to the NEXRAD archive in the United States. ical data at national and international levels in Europe (e.g., These actions should lead to a well-designed and docu- by the EUMETNET OPERA program; Huuskonen et  al. mented data infrastructure and workflow to support collab- 2014), this still features high on the task list for biological orative research and the development of sustainable services. data. Currently, many countries do not store and exchange the complete basic weather-radar data needed to extract Toolbox of classification algorithms. Improving the distinction biological information (polar volume data, also referred between biological and nonbiological targets in weather- to as level-2 data in the United States). Furthermore, data radar data will also benefit meteorologists because biologi- quality substantially differs between countries, and radar cal targets frequently contaminate meteorological data, and settings may not always yield high-quality biological data, clearly (or more comprehensively) excluding “bioscatter” such as when filter settings are too exclusive for the weak will improve meteorological products (Rennie et  al. 2015). (but highly detectable) biological signals or when biologi- However, the classification of biological targets also needs cal signals are removed before data are stored. Finally, data improvement; this can be achieved in part through cross- policies that often vary between countries due to political calibration efforts using different sensors under a broad 916 BioScience • October 2017 / Vol. 67 No. 10 https://academic.oup.com/bioscience Forum range of environmental conditions and across geographic Animal Movement (ENRAM), in facilitating this collabo- regions (Dokter et al. 2011). Furthermore, dual-polarization ration. JFK’s contribution was supported by NSF grant no. radar has great potential for improving target classifica- DGE-1545261. tion (Stepanian et  al. 2016). Finally, robust algorithms for extracting animal migration parameters should be imple- References cited mented into a basic “toolbox” that runs on all weather radars Allan JR, Orosz AP. 2001. The costs of birdstrikes to commercial aviation. in a network. Pages 217–226 in Bird Strike Committee–USA/Canada. Bird Strike Committee Proceedings. University of Nebraska. 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Bayesian echo classification for Australian single- of Western Australia, in Crawley. Nir Sapir is with the Department of polarization weather radar with application to assimilation of radial Evolutionary and Environmental Biology at the University of Haifa, in velocity observations. Journal of Atmospheric and Oceanic Technology Israel. Michał Ciach is affiliated with the Department of Forest Biodiversity 32: 1341–1355. at the University of Agriculture, in Krakow, Poland. Lars B. Pettersson is Reynolds DR, Chapman JW, Harrington R. 2006. The migration of insect with the Biodiversity Unit, Department of Biology, at the University of vectors of plant and animal viruses. Advances in Virus Research Lund, in Sweden. Jeffrey F. Kelly is affiliated with the Oklahoma Biological 67: 453–517. Survey and the Department of Biology at the University of Oklahoma, Shamoun-Baranes J, Bouten W, Buurma L, DeFusco R, Dekker A, Sierdsema in Norman. Hidde Leijnse is with the Royal Netherlands Meteorological H, Sluiter F, van Belle J, van Gasteren H, van Loon E. 2008. Avian Institute, in De Bilt, The Netherlands. 918 BioScience • October 2017 / Vol. 67 No. 10 https://academic.oup.com/bioscience

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