AeroEco Lab Research Highlights 

Sivakumar, A. H., D. Sheldon, K. Winner, C. S. Burt, K. G. Horton

For more than 50 years, US radar aeroecology has largely been restricted to the lower 48 states — until now. Just out in the Proceedings of the Royal Society B, our team, led by high school student Ashwin Sivakumar, takes the first weather surveillance radar view of Alaskan bird migration. To this end, we leverage the untapped potential of weather surveillance radar data to quantify active migration through the airspaces of Alaska. We use over 400 000 NEXRAD radar scans from seven stations across the state between 1995 and 2018 (86% of samples derived from 2013 to 2018) to measure spring and autumn migration intensity, phenology and directionality. 

 

K. G. Horton, B. M. Van Doren, H. J. Albers, A. Farnsworth, D. Sheldon.

Forecasts aren’t just for the weather. Scientists can use weather radar and related technology to chart the journeys of billions of migratory birds, which can help protect these global travelers from a growing array of threats.

In a new breakthrough on this front, a team led by Colorado State University used millions of observations from 143 weather surveillance radars to evaluate a forecasting system for nocturnal bird migration in the United States.

Using these tools, the team discovered that a mere 10 nights of action are required to reduce risk to 50% of avian migrants passing over a given area in spring and autumn. Specific actions are as simple as turning off nonessential outdoor lights.

Conservation Biology published the study, “Near-term ecological forecasting for dynamic aeroconservation of migratory birds,” on April 8. Its release occurs just two weeks before peak migration season for birds in states including Texas and Florida. Colorado’s peak will take place in the first two weeks of May.

How has migration phenology changed in the last 20+ years?

We examine this question in our latest paper in Nature Climate Change. 🔗

 
 
 
 
 

Abstract: Urban green spaces (UGS) often support diverse bird assemblages. Current evidence suggests large UGS that are circular in shape and contain abundant tree canopy cover will support more bird species independent of UGS isolation. Here, we use bird occurrence information from the eBird community-science database over an 18-year period (2002–2019) to estimate annual and seasonal patterns of avian species richness in well-surveyed New York City green spaces. Area was the strongest correlate of annual (n = 102 UGS) and seasonal species richness (n = 43 UGS), whereas shape and isolation lacked significant relationships. Increasing area by 50% resulted in an 11.5% increase in annual and an 8.2% increase in seasonal species richness. There was no evidence that these relationships contained an upper limit. Tree canopy cover was weakly correlated with annual species richness. The richness of nocturnally migrating species was strongly correlated with area in the spring and autumn, especially for non-passerine species. The species richness of nocturnally migrating passerines was strongly correlated with tree canopy cover in the spring, where a 50% increase in canopy cover resulted in a 23.3% increase in species richness. Our findings emphasize the broad importance of area, the value of tree canopy cover for spring migrants, and the limited relevance of shape and isolation. Efforts to enhance area and tree canopy cover will increase the number of resident and migratory bird species, which will likely increase the number of other area-sensitive forest taxa that occur in urban environments.

K. M. Covino,  K. G. Horton,  and S. R. Morris.

Abstract: The availability of detailed information that encompasses the geographic range of a species, spans a long-term temporal range, and yields individual information (e.g., age and sex), is a principle challenge in ecology. To this end, the North American Bird Banding Laboratory maintains a unique and underutilized dataset that can be used to address core questions of phenological change in migratory birds. We used records from 1966 to 2015 to quantify how the timing of migration has shifted in a long-distance migrant, the Black-throated Blue Warbler (Setophaga caerulescens). Additionally, we examined age and sex differences in the timing of migratory movements. We observed that early spring migrants passed through sites ~1.1 days earlier per decade and the peak of spring migration also occurred earlier over the 50 yr of this study. Additionally, phenological change was more rapid with increasing latitude during peak spring migratory periods. During fall, the peak of migration stayed consistent across the 50 yr studied, but the migratory season showed protraction overall. During spring, males consistently migrated earlier than females and adults migrated earlier than young individuals. During fall, there was no difference in timing between males and females, but young birds migrated earlier than adults. Additionally, migration proceeded faster in spring compared with the fall. This study reveals differential strategies in migrant timing, across seasons, age groups, and by sex, and shows that en route adjustments across latitude may account for changes in migrant timing. This basic information about such a fundamental ecological process is crucial to our understanding of migration and we must utilize these unique data to appreciate critical shifts at relevant scales of migration.

High-intensity urban light installation dramatically alters nocturnal bird migration (PNAS 2017)

Van Doren*,B. M., K. G. Horton*, A. M. Dokter, H. Klinck, S. B. Elbin, and A. Farnsworth

*contributed equally to this work

Significance: Artificial light at night is a novel stimulus in the evolutionary history of nocturnal animals. Light pollution can significantly alter these organisms’ behaviors, from migration to foraging to vocal communication. Nocturnally migrating birds are particularly susceptible to artificial light because of adaptations and requirements for navigating and orienting in darkness. However, light’s effects on in-flight behaviors have not been well quantified, especially in urbanized environments. Here we report that an iconic urban light installation dramatically altered multiple behaviors of nocturnally migrating birds—but these effects disappeared when lights were extinguished. We recommend selective removal of light pollution during nights with substantial bird migration to mitigate negative effects on birds, in particular collisions with lighted structures.

Abstract: There are several remote-sensing tools readily available for the study of nocturnally flying animals (e.g., migrating birds), each possessing unique measurement biases. We used three tools (weather surveillance radar, thermal infrared camera, and acoustic recorder) to measure temporal and spatial patterns of nocturnal traffic estimates of flying animals during the spring and fall of 2011 and 2012 in Lewes, Delaware, USA. Our objective was to compare measures among different technologies to better understand their animal detection biases. For radar and thermal imaging, the greatest observed traffic rate tended to occur at, or shortly after, evening twilight, whereas for the acoustic recorder, peak bird flight-calling activity was observed just prior to morning twilight. Comparing traffic rates during the night for all seasons, we found that mean nightly correlations between acoustics and the other two tools were weakly correlated (thermal infrared camera and acoustics, r = 0.004 ± 0.04 SE, n = 100 nights; radar and acoustics, r= 0.14 ± 0.04 SE, n = 101 nights), but highly variable on an individual nightly basis (range = −0.84 to 0.92, range = −0.73 to 0.94). The mean nightly correlations between traffic rates estimated by radar and by thermal infrared camera during the night were more strongly positively correlated (r = 0.39 ± 0.04 SE, n = 125 nights), but also were highly variable for individual nights (range = −0.76 to 0.98). Through comparison with radar data among numerous height intervals, we determined that flying animal height above the ground influenced thermal imaging positively and flight call detections negatively. Moreover, thermal imaging detections decreased with the presence of cloud cover and increased with mean ground flight speed of animals, whereas acoustic detections showed no relationship with cloud cover presence but did decrease with increased flight speed. We found sampling methods to be positively correlated when comparing mean nightly traffic rates across nights. The strength of these correlations generally increased throughout the night, peaking 2–3 hours before morning twilight. Given the convergence of measures by different tools at this time, we suggest that researchers consider sampling flight activity in the hours before morning twilight when differences due to detection biases among sampling tools appear to be minimized.

Abstract: Avian migration monitoring can take on many forms; however, monitoring active nocturnal migration of land birds is limited to a few techniques. Avian nocturnal flight calls are currently the only method for describing migrant composition at the species level. However, as this method develops, more information is needed to understand the sources of variation in call detection. Additionally, few studies examine how detection probabilities differ under varying atmospheric conditions. We use nocturnal flight call recordings from captive individuals to explore the dependence of flight call detection on atmospheric temperature and humidity. Height or distance from origin had the largest influence on call detection, while temperature and humidity also influenced detectability at higher altitudes. Because flight call detection varies with both atmospheric conditions and flight height, improved monitoring across time and space will require correction for these factors to generate standardized metrics of songbird migration.