Modelling the flow of nocturnal bird migration with year-round European weather radar network.

Authors: Raphael Nussbaumer, Lionel Benoit, Gregoire Mariethoz, Felix Liechti, Silke Bauer1 & Baptiste Schmid

Year: 2020

Publication: Biorxiv

Publication Link: https://www.biorxiv.org/content/10.1101/2020.10.13.321844v1

Keywords: biomass flow, weather radar, migration ecology, ornithology, fluid dynamics, interactive visualisation, ecological modelling

Abstract: The movements of migratory birds constitute huge biomass flows that influence ecosystems and human economy, agriculture and health through the transport of energy, nutrients, seeds, and parasites. To better understand the influence on ecosystems and the corresponding services and disservices, we need to characterize and quantify the movements of migratory birds at various spatial and temporal scales. Representing the flow of birds in the air as a fluid, we applied a flow model to interpolated maps of bird density and velocity retrieved from the European weather radar network, covering almost a full year. Using this model, we quantify how many birds take-off, flight and land each night across Europe. Cumulating these daily fluxes of take-off and landing over time, we can summarize the change in the number of birds on the ground over the seasons and the entire year, track waves of bird migration between nights across Europe, and identify regions that see major biomass movements. The resulting numbers are impressive: We estimate that during the breeding season, 187 million (M) more birds (623M arriving and 436M leaving) reside in Western Europe (than during winter), while 452 M more birds departed in autumn (934M leaving and 482M arriving). Our study show-cases the enormous potential of combining interdisciplinary data and methods to elucidate the dynamics of avian migration at various spatial and temporal scales, and once more emphasizes the importance of weather radar data being made available from all European countries.

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