Publications
Meteorological data policies needed to support biodiversity monitoring with weather radar
2022
- Authors:
- Shamoun-Baranes, J., Bauer, S., Chapman, J.W., Desmet, P., Dokter, A.M., Farnsworth, A., van Gasteren, H., Haest, B., Koistinen, J., Kranstauber, B. and Liechti, F., 2022. Meteorological data policies needed to support biodiversity monitoring with weather radar. Bulletin of the American Meteorological Society.
- Date:
- 2022
- Publication:
- Bulletin of the American Meteorological Society.
- Abstract:
- Weather radar networks have great potential for continuous and long-term monitoring of aerial biodiversity of birds, bats, and insects. Biological data from weather radars can support ecological research, inform conservation policy development and implementation, and increase the public’s interest in natural phenomena such as migration. Weather radars are already used to study animal migration, quantify changes in populations, and reduce aerial conflicts between birds and aircraft. Yet efforts to establish a framework for the broad utilization of operational weather radar for biodiversity monitoring are at risk without suitable data policies and infrastructure in place. In Europe, the meteorological and ecological communities have made joint efforts towards sharing and standardizing continent-wide weather radar data. These efforts are now at risk as new meteorological data exchange policies render data useless for biodiversity monitoring. In several other parts of the world, weather radar data are not even available for ecological research. We urge policy makers, funding agencies and meteorological organizations across the world to recognize the full potential of weather radar data. We propose several actions which would ensure the continued capability of weather radar networks worldwide to act as powerful tools for biodiversity monitoring and research.
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A Novel Locality for the Observation of Thousands of Passerine Birds during Spring Migration in Los Angeles County, California
2021
- Authors:
- Terrill, R.S., Dean C. A., Garrett, J., MAxwell, D. J., Hill, L., Farnsworth, A., Dokter, A. M., and Tingley, M. W.
- Date:
- 2021
- Publication:
- Western Birds, 52(4), pp.322–339
- Abstract:
- Avian migration is a spectacular phenomenon, representing the annual movements of billions of birds globally. Because the greatest diversity and numbers of birds migrate at night, opportunities to observe active migration are rare. At a number of localities in North America, however, observers can quantify movements of many typically nocturnal migrants during daylight where they continue after dawn. Such locations have provided much information about species-specific phenology, status, and orientation during migration. Localities where morning flights of land birds can be observed are unevenly distributed, however, and are little reported along the Pacific coast. Here we describe a novel location for the observation of spectacular morning flights of nocturnal migrants during spring migration at Bear Divide, in the western San Gabriel Mountains, Los Angeles County, California. In two years of informal surveys at the site, we have recorded at least one morning with an estimated ~13,500 individual birds passing. Our preliminary analyses suggest that the peak of a species’ migration at Bear Divide is correlated with the latitude of a species’ breeding, being later in the spring as that latitude increases. Our data from Bear Divide provide an independent perspective on migration as quantified by local radar. Further work at this locality may help inform our knowledge of migration phenology and population trends.
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Winds aloft over three water bodies influence spring stopover distributions of migrating birds along the Gulf of Mexico coast
2021
- Authors:
- Clipp, H.L., Buler, J.J., Smolinsky, J.A., Horton, K.G., Farnsworth, A. and Cohen, E.B.
- Date:
- 2021
- Publication:
- The Auk, 138(4), p.ukab051.
- Abstract:
- Migrating birds contend with dynamic wind conditions that ultimately influence most aspects of their migration, from broad-scale movements to individual decisions about where to rest and refuel. We used weather surveillance radar data to measure spring stopover distributions of northward migrating birds along the northern Gulf of Mexico coast and found a strong influence of winds over nonadjacent water bodies, the Caribbean Sea and Atlantic Ocean, along with the contiguous Gulf of Mexico. Specifically, we quantified the relative influence of meridional (north–south) and zonal (west–east) wind components over the 3 water bodies on weekly spring stopover densities along western, central, and eastern regions of the northern Gulf of Mexico coast. Winds over the Caribbean Sea and Atlantic Ocean were just as, or more, influential than winds over the Gulf of Mexico, with the highest stopover densities in the central and eastern regions of the coast following the fastest winds from the east over the Caribbean Sea. In contrast, stopover density along the western region of the coast was most influenced by winds over the Gulf of Mexico, with the highest densities following winds from the south. Our results elucidate the important role of wind conditions over multiple water bodies on region-wide stopover distributions and complement tracking data showing Nearctic–Neotropical birds flying nonstop from South America to the northern Gulf of Mexico coast. Smaller-bodied birds may be particularly sensitive to prevailing wind conditions during nonstop flights over water, with probable orientation and energetic consequences that shape subsequent terrestrial stopover distributions. In the future, the changing climate is likely to alter wind conditions associated with migration, so birds that employ nonstop over-water flight strategies may face growing challenges.
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Bird strikes at commercial airports explained by citizen science and weather radar data
2021
- Authors:
- Nilsson, C., La Sorte, F.A., Dokter, A., Horton, K., Van Doren, B.M., Kolodzinski, J.J., Shamoun‐Baranes, J. and Farnsworth, A.
- Date:
- 2021
- Publication:
- Journal of Applied Ecology, 58(10), pp.2029-2039.
- Abstract:
- 1. Aircraft collisions with birds span the entire history of human aviation, includ- ing fatal collisions during some of the first powered human flights. Much effort has been expended to reduce such collisions, but increased knowledge about bird movements and species occurrence could dramatically improve decision support and proactive measures to reduce them. Migratory movements of birds pose a unique, often overlooked, threat to aviation that is particularly difficult for indi- vidual airports to monitor and predict the occurrence of birds vary extensively in space and time at the local scales of airport responses.
2. We use two publicly available datasets, radar data from the US NEXRAD network characterizing migration movements and eBird data collected by citizen scientists to map bird movements and species composition with low human effort expenditures but high temporal and spatial resolution relative to other large-scale bird survey methods. As a test case, we compare results from weather radar distributions and eBird species composition with detailed bird strike records from three major New York airports.
3. We show that weather radar-based estimates of migration intensity can accu- rately predict the probability of bird strikes, with 80% of the variation in bird strikes across the year explained by the average amount of migratory movements captured on weather radar. We also show that eBird-based estimates of species occurrence can, using species’ body mass and flocking propensity, accurately pre- dict when most damaging strikes occur.
4. Synthesisandapplications.Bybetterunderstandingwhenandwheredifferentbird species occur, airports across the world can predict seasonal periods of collision risks with greater temporal and spatial resolution; such predictions include poten- tial to predict when the most severe and damaging strikes may occur. Our results highlight the power of federating datasets with bird movement and distribution - Download:
Drivers of fatal bird collisions in an urban center
2021
- Authors:
- Benjamin M. Van Doren, David Willard, Mary Hennen, Kyle G. Horton, Erica Stuber, Daniel Sheldon, Ashwin Sivakumar, Julia Wang, Andrew Farnsworth, and Benjamin Winger
- Date:
- 2021
- Publication:
- PNAS
- Abstract:
- Millions of nocturnally migrating birds die each year from collisions with built structures, especially brightly illuminated buildings and communications towers. Reducing this source of mortality requires knowledge of important behavioral, meteorological, and anthropogenic factors, yet we lack an understanding of the interacting roles of migration, artificial lighting, and weather conditions in causing fatal bird collisions. Using two decades of collision surveys and concurrent weather and migration measures, we model numbers of collisions occurring at a large urban building in Chicago. We find that the magnitude of nocturnal bird migration, building light output, and wind conditions are the most important predictors of fatal collisions. The greatest mortality occurred when the building was brightly lit during large nocturnal migration events and when winds concentrated birds along the Chicago lakeshore. We estimate that halving lighted window area decreases collision counts by 11× in spring and 6× in fall. Bird mortality could be reduced by ∼60% at this site by decreasing lighted window area to minimum levels recorded. Our study shows strong support for a relationship between nocturnal migration magnitude and urban bird mortality, mediated by light pollution and local atmospheric conditions. Although our research focuses on a single site, our findings have global implications for reducing or eliminating a critically important cause of bird mortality.
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Weather radars’ role in biodiversity monitoring
2021
- Authors:
- Shamoun-Baranes, J., Bauer, S., Chapman, J.W., Desmet, P., Dokter, A.M., Farnsworth, A., Haest, B., Koistinen, J., Kranstauber, B., Liechti, F. and Mason, T.H.
- Date:
- 2021
- Publication:
- Science, 372(6539), pp.248-248.
- Abstract:
- Biodiversity is changing at an unprecedented rate, and long-term monitoring is key to quantifying these changes and identifying their drivers. Weather radars are an essential tool for meeting these goals. However, recent policy changes make vital data unavailable. Data policy should be adjusted to take into account the broad role that weather radars play beyond meteorology.
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Near‐term ecological forecasting for dynamic aeroconservation of migratory birds
2021
- Authors:
- Horton, K.G., Van Doren, B.M., Albers, H.J., Farnsworth, A. and Sheldon, D., 2021. Near‐term ecological forecasting for dynamic aeroconservation of migratory birds. Conservation Biology, 35(6), pp.1777-1786.
- Date:
- Horton, K.G., Van Doren, B.M., Albers, H.J., Farnsworth, A. and Sheldon, D., 2021. Near‐term ecological forecasting for dynamic aeroconservation of migratory birds. Conservation Biology, 35(6), pp.1777-1786.
- Publication:
- Horton, K.G., Van Doren, B.M., Albers, H.J., Farnsworth, A. and Sheldon, D., 2021. Near‐term ecological forecasting for dynamic aeroconservation of migratory birds. Conservation Biology, 35(6), pp.1777-1786.
- Abstract:
- Near-term ecological forecasting has the potential to mitigate negative impacts of human modifications on wildlife by directing efficient action through relevant and timely predic- tions. We used the U.S. avian migration system to highlight ecological forecasting applica- tions for aeroconservation. We used millions of observations from 143 weather surveil- lance radars to construct and evaluate a migration forecasting system for nocturnal bird migration over the contiguous United States. We identified the number of nights of mitiga- tion required to reduce the risk of aerial hazards to 50% of avian migrants passing a given area in spring and autumn based on dynamic forecasts of migration activity. We also inves- tigated an alternative approach, that is, employing a fixed conservation strategy based on time windows that historically capture 50% of migratory passage. In practice, during both spring and autumn, dynamic forecasts required fewer action nights compared with fixed window selection at all locations (spring: mean of 7.3 more alert days; fall: mean of 12.8 more alert days). This pattern resulted in part from the pulsed nature of bird migration cap- tured in the radar data, where the majority (54.3%) of birds move on 10% of a migration season’s nights. Our results highlight the benefits of near-term ecological forecasting and the potential advantages of dynamic mitigation strategies over static ones, especially in the face of increasing risks to migrating birds from light pollution, wind energy infrastructure, and collisions with structures.
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Predicting bird‐window collisions with weather radar
2021
- Authors:
- Elmore, J.A., Riding, C.S., Horton, K.G., O'Connell, T.J., Farnsworth, A. and Loss, S.R.
- Date:
- 2021
- Publication:
- Journal of Applied Ecology, 58(8), pp.1593-1601.
- Abstract:
- Up to 1 billion birds die annually in the U.S. from window collisions; most of these casualties represent migratory native species. Because this major mortality source likely contributes to the decline of the North American avifauna, mitigation tools are needed that accurately predict real-time collision risk, allowing hazards to be minimized before fatalities occur. We assessed the potential use of weather surveillance radar, an emerging tool increasingly used to study and to predict bird migration, as an early warning system to reduce numbers of bird-window collisions. Based on bird-window collision monitoring in Oklahoma, USA, we show that radar-derived migration variables are associated with nightly numbers of collisions. Across the entire night, numbers of collisions increased with higher migration traffic rate (i.e. numbers of birds crossing a fixed line perpendicular to migration direction), and migration variables for specific periods within the night were also related to nightly collisions.
Synthesis and applications. Our study suggests that radar can be an invaluable tool to predict bird-window collisions and help refine mitigation efforts that reduce collisions such as reducing nighttime lighting emitted from and near buildings. - Download:
A place to land: spatiotemporal drivers of stopover habitat use by migrating birds
2021
- Authors:
- Cohen, E.B., Horton, K.G., Marra, P.P., Clipp, H.L., Farnsworth, A., Smolinsky, J.A., Sheldon, D. and Buler, J.J.
- Date:
- 2021
- Publication:
- Ecology Letters, 24(1), pp.38-49.
- Abstract:
- Migrating birds require en route habitats to rest and refuel. Yet, habitat use has never been inte- grated with passage to understand the factors that determine where and when birds stopover dur- ing spring and autumn migration. Here, we introduce the stopover-to-passage ratio (SPR), the percentage of passage migrants that stop in an area, and use 8 years of data from 12 weather surveillance radars to estimate over 50% SPR during spring and autumn through the Gulf of Mexico and Atlantic coasts of the south-eastern US, the most prominent corridor for North America’s migratory birds. During stopovers, birds concentrated close to the coast during spring and inland in forested landscapes during autumn, suggesting seasonal differences in habitat func- tion and highlighting the vital role of stopover habitats in sustaining migratory communities. Beyond advancing understanding of migration ecology, SPR will facilitate conservation through identification of sites that are disproportionally selected for stopover by migrating birds.
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Two unprecedented auk wrecks in the northwest Atlantic in winter 2012/13
2020
- Authors:
- Diamond, A.W., Mcnair, D.B., Ellis, J.C., Rail, J.F., Whidden, E.S., Kratter, A.W., Courchesne, S.J., Pokras, M.A., Wilhelm, S.I., Kress, S.W. and Farnsworth, A.
- Date:
- 10/15/2020
- Publication:
- Marine Ornithology, 48, pp.185-204.
- Abstract:
- An unprecedented irruption of thousands of Razorbills Alca torda into Florida in winter 2012/13 was followed by a “wreck” of Razorbills and Atlantic Puffins Fratercula arctica in outer Cape Cod, Massachusetts, in January–March 2013. We describe these events using citizen-science sources (eBird and beached-bird surveys) and band recoveries, then we discuss them in relation to extreme weather and oceanographic change. We explored effects on likely source populations using census and monitoring data, along with possible contributions from population increases, reduced food supply, and extreme weather. Winter 2012/13 followed a marine heatwave throughout the northwest Atlantic, whose effects included reduced availability of plankton. We attribute the irruption of Razorbills into Florida partly to delayed effects of Hurricane Sandy, which disrupted their coastal habitat sufficiently to cause starving birds to move south on the Labrador Current as far as Florida. Despite the continuation of anomalously warm ocean temperatures in subsequent years and a reduction in plankton communities in the Bay of Fundy and Gulf of Maine that continues to date, no comparable events have been recorded in subsequent winters; this supports our theory that the delayed effects of Hurricane Sandy contributed to these wrecks. We highlight the power of these datasets to detect and to investigate birds’ responses to extreme and anomalous conditions, which in turn provides insight into the dynamics of rapidly changing ecological systems.
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Computational sustainability: Computing for a better world and a sustainable future
2020
- Authors:
- Gomes, C., Dietterich, T., Barrett, C., Conrad, J., Dilkina, B., Ermon, S., Fang, F., Farnsworth, A., Fern, A., Fern, X. and Fink, D. et al.
- Date:
- 2019
- Publication:
- Communications of the ACM
- Abstract:
- Computer and information scientists join forces with other fields to help solve societal and environmental challenges facing humanity, in pursuit of a sustainable future.
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Migratory flight on the Pacific Flyway: strategies and tendencies of wind drift compensation.
- Authors:
- Newcombe, P.B., Nilsson, C., Lin, T.Y., Winner, K., Bernstein, G., Maji, S., Sheldon, D., Farnsworth, A. and Horton, K.G.
- Date:
- 2019
- Publication:
- Biology Letters
- Abstract:
- Applications of remote sensing data to monitor bird migration usher a new understanding of magnitude and extent of movements across entire flyways. Millions of birds move through the western USA, yet this region is understudied as a migratory corridor. Characterizing movements in the Pacific Flyway offers a unique opportunity to study complementary patterns to those recently highlighted in the Atlantic and Central Flyways. We use weather surveillance radar data from spring and autumn (1995–2018) to examine migrants' behaviours in relation to winds in the Pacific Flyway. Overall, spring migrants tended to drift on winds, but less so at northern latitudes and farther inland from the Pacific coastline. Relationships between winds and autumn flight behaviours were less striking, with no latitudinal or coastal dependencies. Differences in the preferred direction of movement (PDM) and wind direction predicted drift patterns during spring and autumn, with increased drift when wind direction and PDM differences were high. We also observed greater total flight activity through the Pacific Flyway during the spring when compared with the autumn. Such complex relationships among birds’ flight strategies, winds and seasonality highlight the variation within a migration system. Characterizations at these scales complement our understanding of strategies to clarify aerial animal movements.
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Phenology of nocturnal avian migration has shifted at the continental scale
- Authors:
- Horton, K.G., La Sorte, F.A., Sheldon, D., Lin, T.Y., Winner, K., Bernstein, G., Maji, S., Hochachka, W.M. and Farnsworth, A.
- Date:
- 2020
- Publication:
- Nature Climate Change
- Abstract:
- Climate change induced phenological shifts in primary productivity result in trophic mismatches for many organisms with broad implications for ecosystem structure and function. For birds that have a synchronized timing of migration with resource availability, the likelihood that trophic mismatches may generate a phenological response in migration timing increases with climate change5. Despite the importance of a holistic understanding of such systems at large spatial and temporal scales, particularly given a rapidly changing climate, analyses are few, primarily because of limitations in the access to appropriate data. Here we use 24 years of remotely sensed data collected by weather surveillance radar to quantify the response of a nocturnal avian migration system within the contiguous United States to changes in temperature. The average peak migration timing advanced in spring and autumn, and these changes were generally more rapid at higher latitudes. During spring and autumn, warmer seasons were predictive of earlier peak migration dates. Decadal changes in surface temperatures predicted spring changes in migratory timing, with greater warming related to earlier arrivals. This study represents one of the first system-wide examinations during two seasons and comprises measures from hundreds of species that describe migratory timing across a continent. Our findings provide evidence of spatially dynamic phenological shifts that result from climate change.
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Broad-Scale Weather Patterns Encountered during Flight Influence Landbird Stopover Distributions
- Authors:
- Clipp, H.L.; Cohen, E.B.; Smolinsky, J.A.; Horton, K.G.; Farnsworth, A.; Buler, J.J.
- Date:
- 2020
- Publication:
- Remote Sensing
- Abstract:
- The dynamic weather conditions that migrating birds experience during flight likely influence where they stop to rest and refuel, particularly after navigating inhospitable terrain or large water bodies, but effects of weather on stopover patterns remain poorly studied. We examined the influence of broad-scale weather conditions encountered by nocturnally migrating Nearctic-Neotropical birds during northward flight over the Gulf of Mexico (GOM) on subsequent coastal stopover distributions. We categorized nightly weather patterns using historic maps and quantified region-wide densities of birds in stopover habitat with data collected by 10 weather surveillance radars from 2008 to 2015. We found spring weather patterns over the GOM were most often favorable for migrating birds, with winds assisting northward flight, and document regional stopover patterns in response to specific unfavorable weather conditions. For example, Midwest Continental High is characterized by strong northerly winds over the western GOM, resulting in high-density concentrations of migrants along the immediate coastlines of Texas and Louisiana. We show, for the first time, that broad-scale weather experienced during flight influences when and where birds stop to rest and refuel. Linking synoptic weather patterns encountered during flight with stopover distributions contributes to the emerging macro-ecological understanding of bird migration, which is critical to consider in systems undergoing rapid human-induced changes. View Full-Text
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Measuring historical bird migration in the US using archived weather radar data and convolutional neural networks
2019
- Authors:
- Tsung‐Yu Lin, Kevin Winner, Garrett Bernstein, Abhay Mittal, Adriaan M. Dokter, Kyle G. Horton, Cecilia Nilsson, Benjamin M. Van Doren, Andrew Farnsworth, Frank A. La Sorte, Subhransu Maji, and Daniel Sheldon
- Date:
- 2019
- Publication:
- Methods in Ecology and Evolution
- Abstract:
- 1. Large networks of weather radars are comprehensive instruments for studying bird migration. For example, the US WSR‐88D network covers the entire continental US and has archived data since the 1990s. The data can quantify both broad and fine-scale bird movements to address a range of migration ecology questions. However, the problem of automatically discriminating precipitation from biology has significantly limited the ability to conduct biological analyses with historical radar data.
2. We develop MistNet, a deep convolutional neural network to discriminate precipitation from biology in radar scans. Unlike prior machine learning approaches, MistNet makes fine‐scaled predictions and can collect biological information from radar scans that also contain precipitation. MistNet is based on neural networks for images, and includes several architecture components tailored to the unique characteristics of radar data. To avoid a massive human labelling effort, we train MistNet using abundant noisy labels obtained from dual polarization radar data.
3. In historical and contemporary WSR‐88D data, MistNet identifies at least 95.9% of all biomass with a false discovery rate of 1.3%. Dual polarization training data and our radar‐specific architecture components are effective. By retaining biomass that co‐occurs with precipitation in a single radar scan, MistNet retains 15% more biomass than traditional whole‐scan approaches to screening. MistNet is fully automated and can be applied to datasets of millions of radar scans to produce fine‐grained predictions that enable a range of applications, from continent-scale mapping to local analysis of airspace usage.
4. Radar ornithology is advancing rapidly and leading to significant discoveries about continent‐scale patterns of bird movements. General‐purpose and empirically validated methods to quantify biological signals in radar data are essential to the future development of this field. MistNet can enable large‐scale, long‐term, and reproducible measurements of whole migration systems. - Download:
- Online:
- DOI: 10.1111/2041-210X.13280
Nocturnal flight-calling behaviour predicts vulnerability to artificial light in migratory birds
2019
- Authors:
- Benjamin M. Winger , Brian C. Weeks , Andrew Farnsworth , Andrew W. Jones , Mary Hennen and David E. Willard
- Date:
- 2019
- Publication:
- Proceedings of the Royal Society B: Biological Sciences
- Abstract:
- Understanding interactions between biota and the built environment is increasingly important as human modification of the landscape expands in extent and intensity. For migratory birds, collisions with lighted structures are a major cause of mortality, but the mechanisms behind these collisions are poorly understood. Using 40 years of collision records of passerine birds, we investigated the importance of species' behavioural ecologies in predicting rates of building collisions during nocturnal migration through Chicago, IL and Cleveland, OH, USA. We found that the use of nocturnal flight calls is an important predictor of collision risk in nocturnally migrating passerine birds. Species that produce flight calls during nocturnal migration tended to collide with buildings more than expected given their local abundance, whereas those that do not use such communication collided much less frequently. Our results suggest that a stronger attraction response to artificial light at night in species that produce flight calls may mediate these differences in collision rates. Nocturnal flight calls probably evolved to facilitate collective decision-making during navigation, but this same social behaviour may now exacerbate vulnerability to a widespread anthropogenic disturbance. Our results also suggest that social behaviour during migration may reflect poorly understood differences in navigational mechanisms across lineages of birds.
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Holding steady: Little change in intensity or timing of bird migration over the Gulf of Mexico
- Authors:
- Kyle G. Horton Benjamin M. Van Doren Frank A. La Sorte Emily B. Cohen Hannah L. Clipp Jeffrey J. Buler Daniel Fink Jeffrey F. Kelly Andrew Farnsworth
- Date:
- 2019
- Publication:
- Global Change Biology
- Abstract:
- Quantifying the timing and intensity of migratory movements is imperative for understanding impacts of changing landscapes and climates on migratory bird populations. Billions of birds migrate in the Western Hemisphere, but accurately estimating the population size of one migratory species, let alone hundreds, presents numerous obstacles. Here, we quantify the timing, intensity, and distribution of bird migration through one of the largest migration corridors in the Western Hemisphere, the Gulf of Mexico (the Gulf). We further assess whether there have been changes in migration timing or intensity through the Gulf. To achieve this, we integrate citizen science (eBird) observations with 21 years of weather surveillance radar data (1995–2015). We predicted no change in migration timing and a decline in migration intensity across the time series. We estimate that an average of 2.1 billion birds pass through this region each spring en route to Nearctic breeding grounds. Annually, half of these individuals pass through the region in just 18 days, between April 19 and May 7. The western region of the Gulf showed a mean rate of passage 5.4 times higher than the central and eastern regions. We did not detect an overall change in the annual numbers of migrants (2007–2015) or the annual timing of peak migration (1995–2015). However, we found that the earliest seasonal movements through the region occurred significantly earlier over time (1.6 days decade−1). Additionally, body mass and migration distance explained the magnitude of phenological changes, with the most rapid advances occurring with an assemblage of larger‐bodied shorter‐distance migrants. Our results provide baseline information that can be used to advance our understanding of the developing implications of climate change, urbanization, and energy development for migratory bird populations in North America.
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The grand challenges of migration ecology that radar aeroecology can help answer
- Authors:
- Silke Bauer, Judy Shamoun‐Baranes, Cecilia Nilsson, Andrew Farnsworth, Jeffrey F Kelly, Don R Reynolds, Adriaan M Dokter, Jennifer F Krauel, Lars B Petterson, Kyle G Horton, Jason W Chapman (
- Date:
- 2019
- Publication:
- Ecography
- Abstract:
- Many migratory species have experienced substantial declines that resulted from rapid and massive expansions of human structures and activities, habitat alterations and climate change. Migrants are also recognized as an integral component of biodiversity and provide a multitude of services and disservices that are relevant to human agriculture, economy and health. The plethora of recently published studies reflects the need for better fundamental knowledge on migrations and for better management of their ecological and human‐relevant effects. Yet, where are we in providing answers to fundamental questions and societal challenges?
Engaging a broad network of researchers worldwide, we used a horizon‐scan approach to identify the most important challenges which need to be overcome in order to gain a fuller understanding of migration ecology, and which could be addressed using radar aeroecological and macroecological approaches. The top challenges include both long‐standing and novel topics, ranging from fundamental information on migration routes and phenology, orientation and navigation strategies, and the multitude of effects migrants may have on resident communities, to societal challenges, such as protecting or preventing migrant services and disservices, and the conservation of migrants in the face of environmental changes. We outline these challenges, identify the urgency of addressing them and the primary stakeholders – researchers, policy makers and practitioners, or funders of research. - Download:
Flocking behaviour in the twilight ascents of Common Swifts Apus apus
- Authors:
- Cecilia Nilsson, Johan Bäckman, Adriaan M Dokter
- Date:
- 2019
- Publication:
- IBIS
- Abstract:
- Among the many unique flight behaviours of Common Swifts Apus apus, the most puzzling may be their ascents to high altitudes during both dusk and dawn. Twilight ascents have been hypothesized to be functionally related to information acquisition, including integration of celestial orientation cues, high‐altitude visual landmarks and sampling of weather conditions. However, their exact purpose remains unknown. We tracked Common Swifts with tracking radar at their breeding grounds in southern Sweden, and present evidence that during the dusk ascent and dawn descent they often occur in flocks, whereas during the dusk descent and dawn ascent phase they do not. This flocking behaviour suggests that swifts may benefit from conspecific interactions during twilight ascents and descents, possibly through more robust cue acquisition and information exchange in groups, or extending social behaviour also seen in screaming parties before dusk.
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Taking radar Aeroecology into the 21st century
- Authors:
- Judy Shamoun‐Baranes, Cecilia Nilsson, Silke Bauer, Jason Chapman
- Date:
- 2019
- Publication:
- Ecography
- Abstract:
- NA
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Bright lights in the big cities: migratory birds’ exposure to artificial light
- Authors:
- Kyle G Horton, Cecilia Nilsson, Benjamin M Van Doren, Frank A La Sorte, Adriaan M Dokter, Andrew Farnsworth
- Date:
- 2019
- Publication:
- Frontiers in Ecology and the Environment
- Abstract:
- Many species of migratory birds have evolved the ability to migrate at night, and the recent and rapid expansion of artificial light at night has markedly altered the nighttime sky through which they travel. Migrating birds regularly pass through heavily illuminated landscapes, and bright lights affect avian orientation. But risks to migrating birds from artificial light are not spatially or temporally uniform, representing a challenge for mitigating potential hazards and developing action plans to catalog risks at continental scales. We leveraged over two decades of remote‐sensing data collected by weather surveillance radar and satellite‐based sensors to identify locations and times of year when the highest numbers of migrating birds are exposed to light pollution in the contiguous US. Our continental‐scale quantification of light exposure provides a novel opportunity for dynamic and targeted conservation strategies to address the hazards posed by light pollution to nocturnally migrating birds.
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- Online:
- https://doi.org/10.1002/fee.2029
bioRad: biological analysis and visualization of weather radar data
- Authors:
- Adriaan M Dokter, Peter Desmet, Jurriaan H Spaaks, Stijn van Hoey, Lourens Veen, Liesbeth Verlinden, Cecilia Nilsson, Günther Haase, Hidde Leijnse, Andrew Farnsworth, Willem Bouten, Judy Shamoun‐Baranes
- Date:
- 2019
- Publication:
- Ecography
- Abstract:
- Weather surveillance radars are increasingly used for monitoring the movements and abundances of animals in the airspace. However, analysis of weather radar data remains a specialised task that can be technically challenging. Major hurdles are the difficulty of accessing and visualising radar data on a software platform familiar to ecologists and biologists, processing the low‐level data into products that are biologically meaningful, and summarizing these results in standardized measures. To overcome these hurdles, we developed the open source R package bioRad, which provides a toolbox for accessing, visualizing and analyzing weather radar data for biological studies. It provides functionality to access low‐level radar data, process these data into meaningful biological information on animal speeds and directions at different altitudes in the atmosphere, visualize these biological extractions, and calculate further summary statistics. The package aims to standardize methods for extracting and reporting biological signals from weather radars. Here we describe a roadmap for analyzing weather radar data using bioRad. We also define weather radar equivalents for familiar measures used in the field of migration ecology, such as migration traffic rates, and recommend several good practices for reporting these measures. The bioRad package integrates with low‐level data from both the European radar network (OPERA) and the radar network of the United States (NEXRAD). bioRad aims to make weather radar studies in ecology easier and more reproducible, allowing for better inter‐comparability of studies.
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Projected changes in wind assistance under climate change for nocturnally migrating bird populations
- Authors:
- Frank A La Sorte, Kyle G Horton, Cecilia Nilsson, Adriaan M Dokter
- Date:
- 2019
- Publication:
- Global Change Biology
- Abstract:
- Current climate models and observations indicate that atmospheric circulation is being affected by global climate change. To assess how these changes may affect nocturnally migrating bird populations, we need to determine how current patterns of wind assistance at migration altitudes will be enhanced or reduced under future atmospheric conditions. Here, we use information compiled from 143 weather surveillance radars stations within the contiguous United States to estimate the daily altitude, density, and direction of nocturnal migration during the spring and autumn. We intersected this information with wind projections to estimate how wind assistance is expected to change during this century at current migration altitudes. The prevailing westerlies at midlatitudes are projected to increase in strength during spring migration and decrease in strength to a lesser degree during autumn migration. Southerly winds will increase in strength across the continent during both spring and autumn migration, with the strongest gains occurring in the center of the continent. Wind assistance is projected to increase across the central (0.44 m/s; 10.1%) and eastern portions of the continent (0.32 m/s; 9.6%) during spring migration, and wind assistance is projected to decrease within the central (0.32 m/s; 19.3%) and eastern portions of the continent (0.17 m/s; 6.6%) during autumn migration. Thus, across a broad portion of the continent where migration intensity is greatest, the efficiency of nocturnal migration is projected to increase in the spring and decrease in the autumn, potentially affecting time and energy expenditures for many migratory bird species. These findings highlight the importance of placing climate change projections within a relevant ecological context informed through empirical observations, and the need to consider the possibility that climate change may generate both positive and negative implications for natural systems.
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Revealing patterns of nocturnal migration using the European weather radar network
- Authors:
- Cecilia Nilsson, Adriaan M Dokter, Liesbeth Verlinden, Judy Shamoun‐Baranes, Baptiste Schmid, Peter Desmet, Silke Bauer, Jason Chapman, Jose A Alves, Phillip M Stepanian, Nir Sapir, Charlotte Wainwright, Mathieu Boos, Anna Górska, Myles HM Menz, Pedro Rodrigues, Hidde Leijnse, Pavel Zehtindjiev, Robin Brabant, Günther Haase, Nadja Weisshaupt, Michał Ciach, Felix Liechti
- Date:
- 2019
- Publication:
- Ecography
- Abstract:
- Nocturnal avian migration flyways remain an elusive concept, as we have largely lacked methods to map their full extent. We used the network of European weather radars to investigate nocturnal bird movements at the scale of the European flyway. We mapped the main migration directions and showed the intensity of movement across part of Europe by extracting biological information from 70 weather radar stations from northern Scandinavia to Portugal, during the autumn migration season of 2016. On average, over the 20 nights and all sites, 389 birds passed per 1 km transect per hour. The night with highest migration intensity showed an average of 1 621 birds per km per hour passing the radar stations, but there was considerable geographical and temporal variation in migration intensity. The highest intensity of migration was seen in central France. The overall migration directions showed strong southwest components. Migration dynamics were strongly related to synoptic wind conditions. A wind‐related mass migration event occurred immediately after a change in wind conditions, but quickly diminished even when supporting winds continued to prevail. This first continental‐scale study using the European network of weather radars demonstrates the wealth of information available and its potential for investigating large‐scale bird movements, with consequences for ecosystem function, nutrient transfer, human and livestock health, and civil and military aviation.
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A continental system for forecasting bird migration
2018
- Authors:
- Benjamin M. Van Doren, Kyle G. Horton
- Date:
- 2018
- Publication:
- Science
- Abstract:
- Billions of animals cross the globe each year during seasonal migrations, but efforts to monitor them are hampered by the unpredictability of their movements. We developed a bird migration forecast system at a continental scale by leveraging 23 years of spring observations to identify associations between atmospheric conditions and bird migration intensity. Our models explained up to 81% of variation in migration intensity across the United States at altitudes of 0 to 3000 meters, and performance remained high in forecasting events 1 to 7 days in advance (62 to 76% of variation was explained). Avian migratory movements across the United States likely exceed 500 million individuals per night during peak passage. Bird migration forecasts will reduce collisions with buildings, airplanes, and wind turbines; inform a variety of monitoring efforts; and engage the public.
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Birdvox-Full-Night: A Dataset and Benchmark for Avian Flight Call Detection
2018
- Authors:
- V. Lostanlen, J. Salamon, A. Farnsworth, S. Kelling and J. P. Bello
- Date:
- 2018
- Publication:
- IEEE
- Abstract:
- This article addresses the automatic detection of vocal, nocturnally migrating birds from a network of acoustic sensors. Thus far, owing to the lack of annotated continuous recordings, existing methods had been benchmarked in a binary classification setting (presence vs. absence). Instead, with the aim of comparing them in event detection, we release BirdVox-full-night, a dataset of 62 hours of audio comprising 35402 flight calls of nocturnally migrating birds, as recorded from 6 sensors. We find a large performance gap between energy-based detection functions and data-driven machine listening. The best model is a deep convolutional neural network trained with data augmentation. We correlate recall with the density of flight calls over time and frequency and identify the main causes of false alarm.
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Seasonal abundance and survival of North America’s migratory avifauna determined by weather radar
- Authors:
- Adriaan M Dokter, Andrew Farnsworth, Daniel Fink, Viviana Ruiz-Gutierrez, Wesley M Hochachka, Frank A La Sorte, Orin J Robinson, Kenneth V Rosenberg, Steve Kelling
- Date:
- 2018
- Publication:
- Nature Ecology and Evolution
- Abstract:
- Avian migration is one of Earth’s largest processes of biomass transport, involving billions of birds. We estimated continental biomass flows of nocturnal avian migrants across the contiguous United States using a network of 143 weather radars. We show that, relative to biomass leaving in autumn, proportionally more biomass returned in spring across the southern United States than across the northern United States. Neotropical migrants apparently achieved higher survival during the combined migration and non-breeding period, despite an average three- to fourfold longer migration distance, compared with a more northern assemblage of mostly temperate-wintering migrants. Additional mortality expected with longer migration distances was probably offset by high survival in the (sub)tropics. Nearctic–Neotropical migrants relying on a ‘higher survivorship’ life-history strategy may be particularly sensitive to variations in survival on the overwintering grounds, highlighting the need to identify and conserve important non-breeding habitats.
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Navigating north: how body mass and winds shape avian flight behaviours across a North American migratory flyway
- Authors:
- Kyle G. Horton Benjamin M. Van Doren Frank A. La Sorte Daniel Fink Daniel Sheldon Andrew Farnsworth Jeffrey F. Kelly
- Date:
- 2018
- Publication:
- Ecology Letters
- Abstract:
- The migratory patterns of birds have been the focus of ecologists for millennia. What behavioural traits underlie these remarkably consistent movements? Addressing this question is central to advancing our understanding of migratory flight strategies and requires the integration of information across levels of biological organisation, e.g. species to communities. Here, we combine species‐specific observations from the eBird citizen‐science database with observations aggregated from weather surveillance radars during spring migration in central North America. Our results confirm a core prediction of migration theory at an unprecedented national scale: body mass predicts variation in flight strategies across latitudes, with larger‐bodied species flying faster and compensating more for wind drift. We also find evidence that migrants travelling northward earlier in the spring increasingly compensate for wind drift at higher latitudes. This integration of information across biological scales provides new insight into patterns and determinants of broad‐scale flight strategies of migratory birds.
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Field validation of radar systems for monitoring bird migration
- Authors:
- Cecilia Nilsson, Adriaan M Dokter, Baptiste Schmid, Martina Scacco, Liesbeth Verlinden, Johan Bäckman, Günther Haase, Giacomo Dell’Omo, Jason W Chapman, Hidde Leijnse, Felix Liechti
- Date:
- 2018
- Publication:
- Journal of Applied Ecology
- Abstract:
- Advances in information technology are increasing the use of radar as a tool to investigate and monitor bird migration movements. We set up a field campaign to compare and validate outputs from different radar systems. Here we compare the pattern of nocturnal bird migration movements recorded by four different radar systems at a site in southern Sweden. Within the range of the weather radar (WR) Ängelholm, we operated a "BirdScan" (BS) dedicated bird radar, a standard marine radar (MR), and a tracking radar (TR). The measures of nightly migration intensities, provided by three of the radars (WR, BS, MR), corresponded well with respect to the relative seasonal course of migration, while absolute migration intensity agreed reasonably only between WR and BS. Flight directions derived from WR, BS and TR corresponded very well, despite very different sample sizes. Estimated mean ground speeds differed among all four systems. The correspondence among systems was highest under clear sky conditions and at high altitudes. Synthesis and applications. While different radar systems can provide useful information on nocturnal bird migration, they have distinct strengths and weaknesses, and all require supporting data to allow for species level inference. Weather radars continuously detect avian biomass flows across a wide altitude band, making them a useful tool for monitoring and predictive applications at regional to continental scales that do not rely on resolving individuals. BirdScan and marine radar's strengths are in local and low altitude applications, such as collision risks with man-made structures and airport safety, although marine radars should not be trusted for absolute intensities of movement. In quantifying flight behaviour of individuals, tracking radars are the most informative.
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Aeroecology of a solar eclipse
- Authors:
- Nilsson, Cecilia, Horton, Kyle G., Dokter, Adriaan M., Van Doren, Benjamin M. Farnsworth, Andrew
- Date:
- 2018
- Publication:
- Biology Letters
- Abstract:
- Light cues elicit strong responses from nearly all forms of life, perhaps most notably as circadian rhythms entrained by periods of daylight and darkness. Atypical periods of darkness, like solar eclipses, provide rare opportunities to study biological responses to light cues. By using a continental scale radar network, we investigated responses of flying animals to the total solar eclipse of 21 August 2017. We quantified the number of biological targets in the atmosphere at 143 weather radar stations across the continental United States to investigate whether the decrease in light and temperature at an atypical time would initiate a response like that observed at sunset, when activity in the atmosphere usually increases. Overall, biological activity decreased in the period leading to totality, followed by a short low-altitude spike of biological activity during totality in some radars. This pattern suggests that cues associated with the eclipse were insufficient to initiate nocturnal activity comparable to that occurring at sunset but sufficient to suppress diurnal activity.
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Seasonal associations with urban light pollution for nocturnally migrating bird populations
2017
- Authors:
- Frank A. La Sorte, Daniel Fink, Jeffrey J. Buler, Andrew Farnsworth, Sergio A. Cabrera-Cruz
- Date:
- 2017
- Publication:
- Global Change Biology
- Abstract:
- The spatial extent and intensity of artificial light at night (ALAN) has increased worldwide through the growth of urban environments. There is evidence that nocturnally migrating birds are attracted to ALAN, and there is evidence that nocturnally migrating bird populations are more likely to occur in urban areas during migration, especially in the autumn. Here, we test if urban sources of ALAN are responsible, at least in part, for these observed urban associations. We use weekly estimates of diurnal occurrence and relative abundance for 40 nocturnally migrating bird species that breed in forested environments in North America to assess how associations with distance to urban areas and ALAN are defined across the annual cycle. Migratory bird populations presented stronger than expected associations with shorter distances to urban areas during migration, and stronger than expected association with higher levels of ALAN outside and especially within urban areas during migration. These patterns were more pronounced during autumn migration, especially within urban areas. Outside of the two migration periods, migratory bird populations presented stronger than expected associations with longer distances to urban areas, especially during the nonbreeding season, and weaker than expected associations with the highest levels of ALAN outside and especially within urban areas. These findings suggest that ALAN is associated with higher levels of diurnal abundance along the boundaries and within the interior of urban areas during migration, especially in the autumn when juveniles are undertaking their first migration journey. These findings support the conclusion that urban sources of ALAN can broadly effect migratory behavior, emphasizing the need to better understand the implications of ALAN for migratory bird populations.
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How do en route events around the Gulf of Mexico influence migratory landbird populations?
- Authors:
- Emily B Cohen, Wylie C Barrow Jr, Jeffrey J Buler, Jill L Deppe, Andrew Farnsworth, Peter P Marra, Scott R McWilliams, David W Mehlman, R Randy Wilson, Mark S Woodrey, Frank R Moore
- Date:
- 2017
- Publication:
- The Condor
- Abstract:
- Habitats around the Gulf of Mexico (GOM) provide critical resources for Nearctic–Neotropical migratory landbirds, the majority of which travel across or around the GOM every spring and fall as they migrate between temperate breeding grounds in North America and tropical wintering grounds in the Caribbean and Central and South America. At the same time, ecosystems in the GOM are changing rapidly, with unknown consequences for migratory landbird populations, many of which are experiencing population declines. In general, the extent to which events encountered en route limit migratory bird populations is not well understood. At the same time, information from weather surveillance radar, stable isotopes, tracking, eBird, and genetic datasets is increasingly available to address many of the unanswered questions about bird populations that migrate through stopover and airspace habitats in the GOM. We review the state of the science and identify key research needs to understand the impacts of en route events around the GOM region on populations of intercontinental landbird migrants that breed in North America, including: (1) distribution, timing, and habitat associations; (2) habitat characteristics and quality; (3) migratory connectivity; and (4) threats to and current conservation status of airspace and stopover habitats. Finally, we also call for the development of unified and comprehensive long-term monitoring guidelines and international partnerships to advance our understanding of the role of habitats around the GOM in supporting migratory landbird populations moving between temperate breeding grounds and wintering grounds in Mexico, Central and South America, and the Caribbean.
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Where in the air? Aerial habitat use of nocturnally migrating birds
- Authors:
- Kyle G Horton, Benjamin M Van Doren, Phillip M Stepanian, Andrew Farnsworth, Jeffrey F Kelly
- Date:
- 2016
- Publication:
- Biology Letters
- Abstract:
- The lower atmosphere (i.e. aerosphere) is critical habitat for migrant birds. This habitat is vast and little is known about the spatio-temporal patterns of distribution and abundance of migrants in it. Increased human encroachment into the aerosphere makes understanding where and when migratory birds use this airspace a key to reducing human–wildlife conflicts. We use weather surveillance radar to describe large-scale height distributions of nocturnally migrating birds and interpret these distributions as aggregate habitat selection behaviours of individual birds. As such, we detail wind cues that influence selection of flight heights. Using six radars in the eastern USA during the spring (2013–2015) and autumn (2013 and 2014), we found migrants tended to adjust their heights according to favourable wind profit. We found that migrants' flight altitudes correlated most closely with the altitude of maximum wind profit; however, absolute differences in flight heights and height of maximum wind profit were large. Migrants tended to fly slightly higher at inland sites compared with coastal sites during spring, but not during autumn. Migration activity was greater at coastal sites during autumn, but not during spring. This characterization of bird migration represents a critical advance in our understanding of migrant distributions in flight and a new window into habitat selection behaviours.
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The role of atmospheric conditions in the seasonal dynamics of North American migration flyways
2016
- Authors:
- Frank A La Sorte, Daniel Fink, Wesley M Hochachka, Andrew Farnsworth, Amanda D Rodewald, Kenneth V Rosenberg, Brian L Sullivan, David W Winkler, Chris Wood, Steve Kelling
- Date:
- 2014
- Publication:
- Journal of Biogeography
- Abstract:
- Avian migration strategies balance the costs and benefits of annual movements between breeding and wintering grounds. If similar constraints affect a large numbers of species, geographical concentrations of migration routes, or migration flyways, may result. Here we provide the first population-level empirical evaluation of the structure and seasonal dynamics of migration flyways for North American terrestrial birds and their association with atmospheric conditions.
We modelled weekly probability of occurrence for 93 migratory species using spatio-temporal exploratory models and eBird occurrence data for the combined period 2004 to 2011. We used hierarchical cluster analysis to identify species with shared migration routes based on normalized spatio-temporal representations of autumn migration. We summarized atmospheric conditions within flyways using nocturnal wind velocity and bearing estimated at three isobaric levels (725, 825 and 925 mbar) for the combined period 2008 to 2011.
Results
We identified three migration flyways: an eastern and western flyway whose paths shifted westwards in the spring, and a central flyway whose core boundaries overlapped with the eastern flyway and whose width was more constricted in the autumn. The seasonal shift of the eastern flyway created potentially longer migration journeys in the spring, but this longer route coincides with a low-level jet stream that may enhance migration speeds. Atmospheric conditions appeared to have a more limited role in the seasonal dynamics of the western flyway.
Main conclusions
Migration routes for terrestrial species in North America can be organized into three broadly defined migration flyways: a geographically distinct flyway located west of the 103rd meridian and two interrelated flyways located east of the 103rd meridian. Seasonal shifts in flyway locations reflect the influence of looped migration strategies that for the eastern flyway can be explained by the trade-off between minimizing total migration distance while maintaining an association with favourable atmospheric conditions. - Download:
Migration timing and its determinants for nocturnal migratory birds during autumn migration
- Authors:
- Frank A La Sorte, Wesley M Hochachka, Andrew Farnsworth, Daniel Sheldon, Daniel Fink, Jeffrey Geevarghese, Kevin Winner, Benjamin M Van Doren, Steve Kelling
- Date:
- 2015
- Publication:
- Journal of Animal Ecology
- Abstract:
- Summary
1. Migration is a common strategy used by birds that breed in seasonal environments, and multiple environmental and biological factors determine the timing of migration. How these factors operate in combination during autumn migration, which is considered to be under weaker time constraints relative to spring migration, is not clear.
2. Here, we examine the patterns and determinants of migration timing for nocturnal migrants during autumn migration in the north-eastern USA using nocturnal reflectivity data from 12 weather surveillance radar stations and modelled diurnal probability of occurrence for 142 species of nocturnal migrants. We first model the capacity of seasonal atmospheric conditions (wind and precipitation) and ecological productivity (vegetation greenness) to predict autumn migration intensity. We then test predictions, formulated under optimal migration theory, on how migration timing should be related to assemblage-level estimates of body size and total migration distance within the context of dietary guild (insectivore and omnivore) and level of dietary plasticity during autumn migration.
3. Our results indicate seasonal declines in ecological productivity delineate the beginning and end of peak migration, whose intensity is best predicted by the velocity of winds at migration altitudes. Insectivorous migrants departed earlier in the season and, consistent with our predictions, large-bodied and long-distance insectivorous migrants departed the earliest. Contrary to our predictions, large-bodied and some long-distance omnivorous migrants departed later in the season, patterns that were replicated in part by insectivorous migrants that displayed dietary plasticity during autumn migration.
4. Our findings indicate migration timing in the region is dictated by optimality strategies, modified based on the breadth and flexibility of migrant's foraging diets, with declining ecological productivity defining possible resource thresholds during which migration occurs when winds at migration altitudes are mild. These observations provide the basis to assess how avian migration strategies may be affected by adjustments in seasonal patterns of atmospheric circulation and ecological productivity that may occur under global climate change. - Download:
A comparison of similarity-based approaches in the classification of flight calls of four species of North American wood-warblers (Parulidae)
- Authors:
- Sara Keen, Jesse C Ross, Emily T Griffiths, Michael Lanzone, Andrew Farnsworth
- Date:
- 2014
- Publication:
- Ecological Informatics
- Abstract:
- Numerous methods are available for analysis of avian vocalizations, but few research efforts have compared recent methods for calculating and evaluating similarity among calls, particularly those collected in the field. This manuscript compares a suite of methodologies for analyzing flight calls of New World warblers, investigating the effectiveness of four techniques for calculating call similarity: (1) spectrographic cross-correlation, (2) dynamic time warping, (3) Euclidean distance between spectrogram-based feature measurements, and (4) random forest distance between spectrogram-based feature measurements. We tested these methods on flight calls, which are short, structurally simple vocalizations typically used during nocturnal migration, as these signals may contain important ecological or demographic information. Using the four techniques listed above, we classified flight calls from three datasets, one collected from captive birds and two collected from wild birds in the field. Each dataset contained an equal number of calls from four warbler species commonly recorded during acoustic monitoring: American Redstart, Chestnut-sided Warbler, Hooded Warbler, and Ovenbird. Using captive recordings to train the classification models, we created four similarity-based classifiers which were then tested on the captive and field datasets. We show that these classification methods are limited in their ability to successfully classify the calls of these warbler species, and that classification accuracy was lower on field recordings than captive recordings for each of the tested methods. Of the four methods we compared, the random forest technique had the highest classification accuracy, enabling correct classification of 67.6% of field recordings. To compare the performance of the automated techniques to manual classification, the most common method used in flight call research, human experts were also asked to classify calls from each dataset. The experts correctly classified approximately 90% of field recordings, indicating that although the automated techniques are faster, they remain less accurate than manual classification. However, because of the challenges inherent to these data, such as the structural similarity among the flight calls of focal species and the presence of environmental noise in the field recordings, some of the tested automated classification techniques may be acceptable for real-world applications. We believe that this comparison of broadly applicable methodologies provides information that will prove to be useful for analysis, detection and classification of short duration signals. Based on our results, we recommend that a combination of feature measurements and random forest classification can be used to assign flight calls to species, while human experts oversee the process.
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Seasonal changes in the altitudinal distribution of nocturnally migrating birds during autumn migration
- Authors:
- Frank A La Sorte, Wesley M Hochachka, Andrew Farnsworth, Daniel Sheldon, Benjamin M Van Doren, Daniel Fink, Steve Kelling
- Date:
- 2015
- Publication:
- Royal Society Open Science
- Abstract:
- Wind plays a significant role in the flight altitudes selected by nocturnally migrating birds. At mid-latitudes in the Northern Hemisphere, atmospheric conditions are dictated by the polar-front jet stream, whose amplitude increases in the autumn. One consequence for migratory birds is that the region’s prevailing westerly winds become progressively stronger at higher migration altitudes. We expect this seasonality in wind speed to result in migrants occupying progressively lower flight altitudes, which we test using density estimates of nocturnal migrants at 100 m altitudinal intervals from 12 weather surveillance radar stations located in the northeastern USA. Contrary to our expectations, median migration altitudes deviated little across the season, and the variance was lower during the middle of the season and higher during the beginning and especially the end of the season. Early-season migrants included small- to intermediate-sized long-distance migrants in the orders Charadriiformes and Passeriformes, and late-season migrants included large-bodied and intermediate-distance migrants in the order Anseriformes. Therefore, seasonality in the composition of migratory species, and related variation in migration strategies and behaviours, resulted in a convex–concave bounded distribution of migration altitudes. Our results provide a basis for assessing the implications for migratory bird populations of changes in mid-latitude atmospheric conditions probably occurring under global climate change.
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Warmer Summers and Drier Winters Correlate with More Winter Vagrant Purple Gallinules (Porphyrio martinicus) in the North Atlantic Region
- Authors:
- Andrew Farnsworth, Frank A La Sorte, Marshall J Iliff
- Date:
- 2015
- Publication:
- The Wilson Journal of Ornithology
- Abstract:
- Individuals from a diverse array of bird species sometimes occur well outside of their historic distributions. These vagrants, and their patterns of occurrence, may yield valuable insights regarding how birds respond to environmental change. Among the Rallidae, which are champion dispersers, the Purple Gallinule (Porphyrio martinicus) disperses exceptionally long distances. Whereas most Purple Gallinule vagrants occur from April to October, a much smaller number of records represent a more enigmatic vagrancy pattern that occurs from November to February. Using eBird, a global bird-monitoring project, we compiled 77 occurrences of vagrant Purple Gallinules from 1957–2014 during this seasonal window and examined how those occurrences correlated with environmental conditions and population trends. Average temperature anomalies showed significant correlations with patterns of records, with warmer late summer temperatures in particular in Florida and Puerto Rico correlating with more vagrants. Drier conditions in eastern Mexico, especially during winter, showed similar significant relationships. Our results indicate the potential utility of studying vagrants to understand relationships between bird populations and environmental changes, and more importantly highlight the potential for understanding how vagrancy may relate to changes in this species’ distribution under new climate regimes.
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Collaborative Research: Nocturnally migrating songbirds drift when they can and compensate when they must
- Authors:
- Kyle G Horton, Benjamin M Van Doren, Phillip M Stepanian, Wesley M Hochachka, Andrew Farnsworth, Jeffrey F Kelly
- Date:
- 2016
- Publication:
- Scientific Reports
- Abstract:
- The shortest possible migratory route for birds is not always the best route to travel. Substantial research effort has established that birds in captivity are capable of orienting toward the direction of an intended goal, but efforts to examine how free-living birds use navigational information under conditions that potentially make direct flight toward that goal inefficient have been limited in spatiotemporal scales and in the number of individuals observed because of logistical and technological limitations. Using novel and recently developed techniques for analysis of Doppler polarimetric weather surveillance radar data, we examined two impediments for nocturnally migrating songbirds in eastern North America following shortest-distance routes: crosswinds and oceans. We found that migrants in flight often drifted sideways on crosswinds, but most strongly compensated for drift when near the Atlantic coast. Coastal migrants’ tendency to compensate for wind drift also increased through the night, while no strong temporal differences were observed at inland sites. Such behaviors suggest that birds migrate in an adaptive way to conserve energy by assessing while airborne the degree to which they must compensate for wind drift.
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Wind drift explains the reoriented morning flights of songbirds
- Authors:
- Benjamin M Van Doren, Kyle G Horton, Phillip M Stepanian, David S Mizrahi, Andrew Farnsworth
- Date:
- 2016
- Publication:
- Behavioral Ecology
- Abstract:
- Remote sensors such as Doppler radars are providing novel insights into the migrations of diverse animal taxa, but limits in scope and sensitivity can hamper the utility of these tools. For example, studies investigating whether songbirds compensate effectively for wind displacement during nocturnal migration have been challenged by the need to assess behavior on a large scale. In addition, these studies typically overlook the potential role low-altitude diurnal flights play in dealing with unfavorable winds. In such cases, a combination of approaches—new and traditional—may be necessary to understand behavior more completely. Here, we unite ground-based visual observations with a new radar analysis method to investigate how songbirds deal with crosswinds over the northeast United States. We find that nocturnally migrating birds experienced significant wind drift, even though they often flew at 90° or more to the wind direction. Significantly, more birds undertook reoriented diurnal flights after nocturnal wind drift, and wind influence, nocturnal migration intensity, and time of season together explained the majority of variation in counts of these “morning flights.” This study shows that bird behavior during migration can be strongly shaped by the danger of wind drift and that some songbird species respond to drift with reoriented diurnal migratory flights. Knowledge of birds’ interactions with wind is essential for successfully modeling migratory behavior and assessing the risks associated with changing habitats and meteorological patterns. Furthermore, an understanding of the degree to which drift defines migratory behaviors may have value across animal taxa.
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The implications of mid‐latitude climate extremes for North American migratory bird populations
- Authors:
- Frank A La Sorte, Wesley M Hochachka, Andrew Farnsworth, André A Dhondt, Daniel Sheldon
- Date:
- 2016
- Publication:
- Ecosphere
- Abstract:
- Mid-latitude climate extremes are projected to increase in frequency under global climate change. How this may affect migratory bird populations is not well understood. The mid-latitudes of North America experienced an extreme warming event during March 2012 that advanced the spring phenology of ecological productivity, resulting in lower levels of productivity during the summer. Here, we test the predictions that: (1) short-distance migratory birds, due to geographic proximity and more flexible migratory behavior, should advance their spring migration phenology; and (2) breeding populations, due to lower summer productivity, should have reduced occurrences. We used occurrence data for 353 bird species from the eBird database to calculate weekly occurrence anomalies for 2012 relative to the 2010–2014 average. We identified species having unusually large positive occurrence anomalies during March 2012 and species having unusually large negative occurrence anomalies during July–August 2012. For each category, we summarized migration strategies, geographic distributions, and annual associations with temperature and ecological productivity. Short-distance migrants whose winter and breeding ranges intersect the mid-latitudes advanced their spring migration phenology during March (n = 21). Long-distance migrants whose winter and breeding distributions were weakly associated with the mid-latitudes had lower occurrences during the summer (n = 32). Five species were shared between the two categories. Within species’ winter ranges, temperature and ecological productivity were higher than expected during March; within species’ breeding ranges, ecological productivity was lower than expected during the summer. These differences were strongest for the 21 short-distance migrants. Following our expectations, mid-latitude climate extremes and associated ecological consequences broadly affected avian migration and breeding activities within the region. Our findings suggest short-distance migrants are more flexible and resilient, whereas populations of long-distance migrants are at a distinct disadvantage, which may intensify if the frequency of these events increases.
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A characterization of autumn nocturnal migration detected by weather surveillance radars in the northeastern USA
- Authors:
- Andrew Farnsworth, Benjamin M. Van Doren, Wesley M. Hochachka, Daniel Sheldon, Kevin Winner, Jed Irvine, Jeffrey Geevarghese, Steve Kelling
- Date:
- 2016
- Publication:
- Ecological Application
- Abstract:
- Billions of birds migrate at night over North America each year. However, few studies have described the phenology of these movements, such as magnitudes, directions, and speeds, for more than one migration season and at regional scales. In this study, we characterize density, direction, and speed of nocturnally migrating birds using data from 13 weather surveillance radars in the autumns of 2010 and 2011 in the northeastern USA. After screening radar data to remove precipitation, we applied a recently developed algorithm for characterizing velocity profiles with previously developed methods to document bird migration. Many hourly radar scans contained windborne “contamination,” and these scans also exhibited generally low overall reflectivities. Hourly scans dominated by birds showed nightly and seasonal patterns that differed markedly from those of low reflectivity scans. Bird migration occurred during many nights, but a smaller number of nights with large movements of birds defined regional nocturnal migration. Densities varied by date, time, and location but peaked in the second and third deciles of night during the autumn period when the most birds were migrating. Migration track (the direction to which birds moved) shifted within nights from south-southwesterly to southwesterly during the seasonal migration peaks; this shift was not consistent with a similar shift in wind direction. Migration speeds varied within nights, although not closely with wind speed. Airspeeds increased during the night; groundspeeds were highest between the second and third deciles of night, when the greatest density of birds was migrating. Airspeeds and groundspeeds increased during the fall season, although groundspeeds fluctuated considerably with prevailing winds. Significant positive correlations characterized relationships among bird densities at southern coastal radar stations and northern inland radar stations. The quantitative descriptions of broadscale nocturnal migration patterns presented here will be essential for biological and conservation applications. These descriptions help to define migration phenology in time and space, fill knowledge gaps in avian annual cycles, and are useful for monitoring long-term population trends of migrants. Furthermore, these descriptions will aid in assessing potential risks to migrants, particularly from structures with which birds collide and artificial lighting that disorients migrants.
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Can Nocturnal Flight Calls of the Migrating Songbird, American Redstart, Encode Sexual Dimorphism and Individual Identity?
- Authors:
- Emily T Griffiths, Sara C Keen, Michael Lanzone, Andrew Farnsworth
- Date:
- 2016
- Publication:
- PLoS ONE
- Abstract:
- Bird species often use flight calls to engage in social behavior, for instance maintain group cohesion and to signal individual identity, kin or social associations, or breeding status of the caller. Additional uses also exist, in particular among migrating songbirds for communication during nocturnal migration. However, our understanding of the information that these vocalizations convey is incomplete, especially in nocturnal scenarios. To examine whether information about signaler traits could be encoded in flight calls we quantified several acoustic characteristics from calls of a nocturnally migrating songbird, the American Redstart. We recorded calls from temporarily captured wild specimens during mist-netting at the Powdermill Avian Research Center in Rector, PA. We measured call similarity among and within individuals, genders, and age groups. Calls from the same individual were significantly more similar to one another than to the calls of other individuals, and calls were significantly more similar among individuals of the same sex than between sexes. Flight calls from hatching-year and after hatching-year individuals were not significantly different. Our results suggest that American Redstart flight calls may carry identifiers of gender and individual identity. To our knowledge, this is the first evidence of individuality or sexual dimorphism in the flight calls of a migratory songbird. Furthermore, our results suggest that flight calls may have more explicit functions beyond simple group contact and cohesion. Nocturnal migration may require coordination among numerous individuals, and the use of flight calls to transmit information among intra- and conspecifics could be advantageous. Applying approaches that account for such individual and gender information may enable more advanced research using acoustic monitoring.
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Innovative Visualizations Shed Light on Avian Nocturnal Migration
- Authors:
- Judy Shamoun-Baranes*, Andrew Farnsworth*, Bart Aelterman, Jose A Alves, Kevin Azijn, Garrett Bernstein, Sérgio Branco, Peter Desmet, Adriaan M Dokter, Kyle Horton, Steve Kelling, Jeffrey F Kelly, Hidde Leijnse, Jingjing Rong, Daniel Sheldon, Wouter Van den Broeck, Jan Klaas Van Den Meersche, Benjamin Mark Van Doren, Hans van Gasteren
- Date:
- 2016
- Publication:
- PLoS ONE
- Abstract:
- Globally, billions of flying animals undergo seasonal migrations, many of which occur at night. The temporal and spatial scales at which migrations occur and our inability to directly observe these nocturnal movements makes monitoring and characterizing this critical period in migratory animals’ life cycles difficult. Remote sensing, therefore, has played an important role in our understanding of large-scale nocturnal bird migrations. Weather surveillance radar networks in Europe and North America have great potential for long-term low-cost monitoring of bird migration at scales that have previously been impossible to achieve. Such long-term monitoring, however, poses a number of challenges for the ornithological and ecological communities: how does one take advantage of this vast data resource, integrate information across multiple sensors and large spatial and temporal scales, and visually represent the data for interpretation and dissemination, considering the dynamic nature of migration? We assembled an interdisciplinary team of ecologists, meteorologists, computer scientists, and graphic designers to develop two different flow visualizations, which are interactive and open source, in order to create novel representations of broad-front nocturnal bird migration to address a primary impediment to long-term, large-scale nocturnal migration monitoring. We have applied these visualization techniques to mass bird migration events recorded by two different weather surveillance radar networks covering regions in Europe and North America. These applications show the flexibility and portability of such an approach. The visualizations provide an intuitive representation of the scale and dynamics of these complex systems, are easily accessible for a broad interest group, and are biologically insightful. Additionally, they facilitate fundamental ecological research, conservation, mitigation of human–wildlife conflicts, improvement of meteorological products, and public outreach, education, and engagement.
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Seasonal differences in landbird migration strategies
- Authors:
- Kyle G Horton, Benjamin M Van Doren, Phillip M Stepanian, Andrew Farnsworth, Jeffrey F Kelly
- Date:
- 2016
- Publication:
- Auk
- Abstract:
- Migrating birds make strategic decisions at multiple temporal and spatial scales. They must select flight altitudes, speeds, and orientations in order to maintain preferred directions of movement and to minimize energy expenditure and risk. Spring flights follow a rapid phenology, but how this rapid transit translates to in-flight decisions is not clear. We described flight strategies of nocturnally migrating landbirds using 6 weather surveillance radars during spring (2013–2015) and fall (2013–2014) migratory periods in the eastern United States to investigate seasonal decision-making patterns and how climate change may influence these trends. During spring, we found groundspeed and airspeed of migrants to be significantly higher than those of fall migrants; compensation for wind drift was also significantly greater during spring. Our results indicate that birds make more rapid and precise flights in spring that are only partially explained by meteorological phenomena. Future applications at greater spatial scales will allow direct comparisons of in-flight behaviors with predictions from migration theory.
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Detecting Migrating Birds at Night
2016
- Authors:
- Jia-Bin Huang, Rich Caruana, Andrew Farnsworth, Steve Kelling, and Narendra Ahuja
- Date:
- 2016
- Publication:
- Conference on Computer Vision and Pattern Recognition
- Abstract:
- Bird migration is a critical indicator of environmental health, biodiversity, and climate change. Existing techniques for monitoring bird migration are either expensive (e.g., satellite tracking), labor-intensive (e.g., moon watching), indirect and thus less accurate (e.g., weather radar), or intrusive (e.g., attaching geolocators on captured birds). In this paper, we present a vision-based system for detecting migrating birds in flight at night. Our system takes stereo videos of the night sky as inputs, detects multiple flying birds and estimates their orientations, speeds, and altitudes. The main challenge lies in detecting flying birds of unknown trajectories under high noise level due to the low-light environment. We address this problem by incorporating stereo constraints for rejecting physically implausible configurations and gathering evidence from two (or more) views. Specifically, we develop a robust stereo-based 3D line fitting algorithm for geometric verification and a deformable part response accumulation strategy for trajectory verification. We demonstrate the effectiveness of the proposed approach through quantitative evaluation of real videos of birds migrating at night collected with near-infrared cameras.
- Download:
- Bird_CVPR_2016.pdf
- Online:
- http://cvpr2016.thecvf.com
Autumn morning flights of migrant songbirds in the northeastern United States are linked to nocturnal migration and winds aloft
2015
- Authors:
- Benjamin M. Van Doren, Daniel Sheldon, Jeffrey Geevarghese, Wesley M. Hochachka, and Andrew Farnsworth
- Date:
- 2015
- Publication:
- The Auk
- Abstract:
- Many passerines that typically migrate at night also engage in migratory flights just after sunrise. These widely observed “morning flights” often involve birds flying in directions other than those aimed toward their ultimate destinations, especially in coastal areas. Morning flights have received little formal investigation, and their study may improve our understanding of how birds orient themselves during and after nocturnal movements and how they use stopover habitat. We studied autumn morning flights in the northeastern United States to identify associations between the number of birds undertaking morning flights and the magnitude of nocturnal migratory movements, nocturnal winds, and local topography. Our analyses included observations of more than 15,000 passerines at 7 locations. We found positive relationships between morning flight size and nocturnal migration density and winds aloft: Significantly more birds flew following larger nocturnal movements, quantified from weather surveillance radar and recordings of nocturnal flight calls, and after stronger nocturnal crosswinds. We also found consistent differences in morning flight size and direction among sites. These patterns are consistent with migrants engaging in morning flight as a corrective measure following displacement by nocturnal winds and to search for suitable stopover habitat.
- Download:
- Van-Doren-et-al.-2015-Auk1.pdf
Reconstructing Velocities of Migrating Birds from Weather Radar – A Case Study in Computational Sustainability
2014
- Authors:
- Andrew Farnsworth, Daniel Sheldon, Jeffrey Geevarghese, Jed Irvine, Benjamin Van Doren, Kevin Webb, Thomas G Dietterich, and Steve Kelling
- Date:
- 2014
- Publication:
- AI Magazine
- Abstract:
- Bird migration occurs at the largest of global scales, but monitoring such movements can be challenging. In the US there is an operational network of weather radars providing freely accessible data for monitoring meteorological phenomena in the atmosphere. Individual radars are sensitive enough to detect birds, and can provide insight into migratory behaviors of birds at scales that are not possible using other sensors. Archived data from the WSR-88D network of US weather radars hold valuable and detailed information about the continent-scale migratory movements of birds over the last 20 years. However, significant technical challenges must be overcome to understand this information and harness its potential for science and conservation. We describe recent work on an AI system to quantify bird migration using radar data, which is part of the larger BirdCast project to model and forecast bird migration at large scales using radar, weather, and citizen science data.
Approximate Bayesian Inference for Reconstructing Velocities of Migrating Birds from Weather Radar
2013
- Authors:
- SHELDON, D.; FARNSWORTH, A.; IRVINE, J.; VAN DOREN, B.; WEBB, K.; DIETTERICH, T.; and KELLING, S.
- Date:
- 2013
- Publication:
- AAAI Conference on Artificial Intelligence, North America, jun. 2013.
- Abstract:
- Archived data from the WSR-88D network of weather radars in the US hold detailed information about the continent-scale migratory movements of birds over the last 20 years. However, significant technical challenges must be overcome to understand this information and harness its potential for science and conservation. We present an approximate Bayesian inference algorithm to reconstruct the velocity fields of birds migrating in the vicinity of a radar station. This is part of a larger project to quantify bird migration at large scales using weather radar data.
Collective Graphical Models
2012
- Authors:
- Sheldon, D., and T.G. Dietterich
- Date:
- 2012
- Publication:
- Neural Information Processing Systems (NIPS), Grenada, Spain 12-15 December 2011
- Abstract:
- There are many settings in which we wish to fit a model of the behavior of individuals but where our data consist only of aggregate information (counts or low-dimensional contingency tables). This paper introduces Collective Graphical Models—a framework for modeling and probabilistic inference that operates directly on the sufficient statistics of the individual model. We derive a highly-efficient Gibbs sampling algorithm for sampling from the posterior distribution of the sufficient statistics conditioned on noisy aggregate observations, prove its correctness, and demonstrate its effectiveness experimentally.
- Download:
- Collective-Graphical-Models.pdf
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