A characterization of autumn nocturnal migration detected by weather surveillance radars in the northeasternUSA

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.

Atmospheric conditions create freeways, detours and tailbacks for migrating birds

“…This is true at geographical bottlenecks and leading lines for migrant birds as well as more inland migration sites (Allen et al 1996; Shamoun-Baranes et al 2006). The ability to predict migration fluxes of a range of nocturnal migrants based on local weather (Erni et al 2002; van Belle et al 2007) strongly supports the proposition that birds will have similar responses to weather within certain periods of time and parts of a flyway (Farnsworth et al 2016). Differences in flight capacity of different species, for example due to body mass and wing shape, are probably most influential in shaping species-specific flight behaviour and route choice at local (Vansteelant et al 2014), regional (Panuccio et al 2017) and flyway-scale.…”

“…While citizen science networks can help determine species composition of migratory fluxes observed by radar. Interdisciplinary research networks such as ENRAM (the European Network for the Radar Surveillance of Animal Movement) and BirdCast are working on moving these developments forward (Shamoun-Baranes et al 2014; La Sorte et al 2015a; Farnsworth et al 2016). Combining knowledge about individual based behaviour with the quantification of spatial and temporal flows of migration will help answer macro-ecological questions regarding species distribution patterns (Kelly and Horton 2016).…”

Environmental effects on flying migrants revealed by radar

“…NEXRAD) and Europe (i.e. OPERA), which successfully monitor mass movements of aerial organisms over regional (Dokter et al 2011, Farnsworth et al 2016, Hu et al 2016) and continental scales (Lowery and Newman 1966, Van Doren and Horton 2018, Nilsson et al 2019), the scarcity of radar studies from the African continent, most of Asia and South America limits our knowledge of animal aeroecology in these vast areas. The development of processing and analytical methodologies, as well as knowledge sharing and inter-disciplinary data integration for identifying and tracking aerial migrants across Europe was conducted by the COST (European Cooperation in Science and Technology) action ENRAM (European Network for the Radar surveillance of Animal Movement in Europe; <www.enram.eu>) during 2013-2017.…”

MistNet: Measuring historical bird migration in the US using archived weather radar data and convolutional neural networks

“…Early WSR-88D studies demonstrated how to detect and quantify bird movements but required substantial manual effort, primarily to screen radar images for precipitation and other unwanted targets prior to analysis (Gauthreaux & Belser, 1998;Gauthreaux et al, 2003). Human interpretation of images has persisted into most modern analyses (Buler & Dawson, 2014;Buler & Diehl, 2009;Buler et al, 2012;Farnsworth et al, 2016;Horton et al, 2018;McLaren et al, 2018;Van Doren et al, 2017) and is a substantial barrier to very large-scale research with WSR-88D data, for example, the complete analysis of 200 million historical data files.…”