Revealing patterns of nocturnal migration using the European weather radar network

Cecilia Nilsson,Adriaan M Dokter,Nir Sapir,Judy Shamoun‐Baranes,Pedro Rodrigues,Nadja Weisshaupt,Baptiste Schmid,Michał Ciach,Günther Haase,Phillip M Stepanian,Anna Górska,Silke Bauer,Mathieu Boos,Peter Desmet,Liesbeth Verlinden,Myles H M Menz,Pavel Zehtindjiev,R Brabant ,Jason W Chapman ,H Leijnse ,Charlotte E Wainwright ,José A Alves ,Félix Liechti

doi:10.1111/ecog.04003

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 1621 birds km–1 h–1 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.

Highlights

Billions of mammals, birds, insects and other animals make seasonal round trips between their breeding and non-breeding sites each year, with multitudinous effects on populations, communities and ecosystems (Bauer and Hoye 2014, Hu et al 2016)
Together with the calculation of the mean directions of the movement, the western and central parts of the nocturnal migration flyway over Europe are mapped, and additional information is provided from a single site in SE Europe (Varna, Bulgaria)
Previous methods for mapping large-scale spatial patterns of nocturnal bird migration over Europe have been limited because of data scarcity, for example when deducing spatial patterns from ring recoveries of a few individuals (Hedenström and Pettersson 1987) or due to limited and often poor spatial coverage as in studies integrating radar and infrared measurements or moon watching at individual sites (Bolshakov and Dolnik 1985)

Summary

Introduction

Birds, insects and other animals make seasonal round trips between their breeding and non-breeding sites each year, with multitudinous effects on populations, communities and ecosystems (Bauer and Hoye 2014, Hu et al 2016). Mapping the large-scale spatial variation (locations, directions, routes) and variable timing (phenology in relation to weather and location) of migration has several important applications. From a perspective of human safety, large-scale migration information can improve military and civil aviation safety (ShamounBaranes et al 2017) and provide a basis for mapping and predicting the spread of pests and disease vectors (Bauer et al 2017). The sheer magnitude of migratory movements, both in terms of numbers of animals involved and the spatial and temporal scales over which this process takes place, creates logistic, technical and technological challenges to map migration and to reliably quantify its main properties

Methods

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Discussion

Conclusion