Radar ornithology

The Swiss Ornithological Institute has carried out radar-based studies in Europe, the Near East, in Africa and in North America, enabling unique insights into the patterns and strategies of bird migration. These studies have, for example, revealed how birds deal with barrier crossings and gave clues about their choices of flight elevation and responses to wind and other weather variables. Next to basic animal migration research, environmental impact assessments are also an important part of our work (e.g. impact of tall human-made structures like wind turbines). Over the last years, the radar systems we use have become suitable for investigating aerial insect and bat movements, a topic of increasing importance in the ongoing biodiversity crisis. We have also developed, and currently lead, international partnerships of radar data research groups and private data owners, allowing identification of broad-scale patterns of aerial animal biomass flow and its drivers. We strive to integrate this knowledge through aero-ecological models.

Our radar studies aim at:

• Developing automatic radar-based tools to monitor the spatial and temporal dynamics of (aerial) migratory animals
• Understanding the environmental and anthropogenic influences shaping these spatiotemporal movements and dynamics
• Predicting future short- and long-term dynamics and changes in the timing, direction and abundance of migratory birds, insects, and bats, also in response to anthropogenic change
• Contributing to improving radar systems for automatic real-time recording, analysis and forecast of airborne animal migration
• Contributing to improving software for automatic classification and identification of different species or groups of species (e.g. passerines, waterfowl, insects, bats) vogelwarte.ch/radartechnology

We use small-scale (primarily Birdscan MR1) vertical-looking radars to quantify the number of animals across various height intervals. The temporal variation of the echo intensity during the transit of the animal through the beam is related to animal properties (such as flight pattern, wing beat frequencies, size, and shape). We can use these variations in echo intensity to identify whether these animals are insects, bats or one of several subgroups of birds, such as passerines, waders, swifts, or large birds. We also identify their flight directions, ground speed, and altitudes, allowing quantification and differentiation of local and migratory movements across different height intervals.

The Birdscan MR1 is a commercial product that was developed in collaboration with the Swiss Ornithological Institute. A growing number of research groups and private companies now own and use the Birdscan MR1 radar for animal migration research and environmental impact assessments. To promote knowledge exchange and sharing of code, tools, and results from new studies, the Swiss Ornithological institute has set up and leads the Birdscan Community, which brings together all interested researchers through regular meetings. A project benefitting from this community is the MoveInEurope project which was launched to quantify INsect biomass, abundance, activity and MOVEment patterns across Europe.

The Swiss Ornithological Institute has also been continuously recording migration data with a Birdscan MR1 for several years and streams these data on its website, exemplified by the image below.

Weather radars operated by meteorological institutes not only measure the quantity of precipitation but can be used to study the movements of animals aloft. Organised in national networks, their large surveyed areas (5-100 km diameter) enable us to quantify the biomass flows of aerial migrants from regional to continental scales across Europe and North America, over timescales from minutes to years.

With our involvement in two European research projects (ENRAM and Globam), the Swiss Ornithological institute is a leading partner to promote the accessibility and harmonisation of European weather radar data, and their interoperability with small-scale radar, in order to quantify the biomass flows at a continental scale. A visualization of the aerial flow of bird migration across Western Europe, exemplified for the year 2018, can be found below and in more detail under this link.

Quantifying the spatially and temporally explicit patterns of bird, bat, and insect movements is a prerequisite to understanding environmental impacts on the continent-wide migration. Only a continuous and automatic monitoring of migration by radar allows systematic recording also of the rare but very specific events of mass movements, which often are only mentioned as anecdotes. For insects and bats, there is a particularly immense lack of knowledge about movement patterns. Modelling and forecasting of movements are important for basic research, for avoiding collision with aviation and tall human-made structures, and for mitigating against other anthropogenic threats such as light pollution.

• Simon Hirschhofer
• Thomas Steuri
• Silke Bauer, Swiss Federal Institute for Forest, Snow and Landscape Research WSL
• Steffen Hahn