High-Resolution Spatial Distribution of Bird Movements Estimated from a Weather Radar Network

Bart Kranstauber,Liesbeth Verlinden,Willem Bouten,Adriaan M Dokter,Berend-Christiaan Wijers,Hidde Leijnse,Judy Shamoun-Baranes

doi:10.3390/rs12040635

Bart Kranstauber, Liesbeth Verlinden + Show 5 more

Open Access

https://doi.org/10.3390/rs12040635

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Abstract

Weather radars provide detailed information on aerial movements of organisms. However, interpreting fine-scale radar imagery remains challenging because of changes in aerial sampling altitude with distance from the radar. Fine-scale radar imagery has primarily been used to assess mass exodus at sunset to study stopover habitat associations. Here, we present a method that enables a more intuitive integration of information across elevation scans projected in a two-dimensional spatial image of fine-scale radar reflectivity. We applied this method on nights of intense bird migration to demonstrate how the spatial distribution of migrants can be explored at finer spatial scales and across multiple radars during the higher flying en-route phase of migration. The resulting reflectivity maps enable explorative analysis of factors influencing their regional and fine-scale distribution. We illustrate the method’s application by generating time-series of composites of up to 20 radars, achieving a nearly complete spatial coverage of a large part of Northwest Europe. These visualizations are highly useful in interpreting regional-scale migration patterns and provide detailed information on bird movements in the landscape and aerial environment.

Highlights

Quantitative information about the spatio-temporal distribution of migratory birds is important for conservation and reducing human-wildlife conflicts [1,2]
The effect of vertical integration was evident from the result that the donut shape visible in individual scans (Figure 1B,C) was no longer visible in the vertically integrated density (VID) product (Figure 3)
The spatial VID estimate highlighted a region of high migratory density in the southeast of the Netherlands that was only visible in a limited number of scans as for most scans, the radar beam was either too low or too high (e.g., Figure 1C)

Summary

Introduction

Quantitative information about the spatio-temporal distribution of migratory birds is important for conservation and reducing human-wildlife conflicts [1,2]. Of the variety of methods used to study migration, only a few are suitable to provide insight into spatio-temporal changes in abundance of migrants, especially across large regions and across a broad range of avian taxa; one highly suitable method is the use of networks of weather radars, e.g., [3,4,5]. Recent studies using weather radars have provided insight into questions that require a broad-scale perspective on migration and movement, such as the influence of light pollution on broad-front migration [6,7], the seasonal changes in population sizes and routes [3], spatio-temporal variation in migration patterns [5], and the decline of migratory populations [8]. In Europe, there are already 164 radars that regularly exchange data in the Operational Programme for the Exchange of Weather Radar (OPERA) network [10], while there are 160 in the North American Next-Generation

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