When weather radar sees more than rain:
the GLOBAM story
How GloBAM turned hidden migration into timely decisions for conservation, aviation and wind energy
A second forecast in the night sky
On a dry spring night, weather radar can still return a dense field of echoes. They are not all clouds or rain. Many come from birds and insects crossing the sky, sometimes in numbers impossible to see or count from the ground.
Every year, trillions of aerial migrants move within and between continents. Their journeys connect ecosystems, transport nutrients and biomass, and support processes such as pollination. Yet many migratory populations are declining, as their movements and habitats are increasingly affected by climate change, expanding cities, artificial light and energy infrastructure.
GloBAM set out to make this largely invisible movement measurable. Researchers in Europe and the United States used continental networks of weather radars to study the movements of birds, insects and bats across timescales ranging from individual nights to years.
From the radar signals, researchers could estimate the intensity, direction, altitude and speed of migration. By comparing these patterns with weather, climate and landscapes, the project investigated when animals move, the conditions they encounter and how human activities affect their journeys.
Turning radar echoes into usable biodiversity information required expertise in migration ecology, meteorology, computing and data engineering. Researchers had to distinguish biological signals from rain, process data consistently across meteorological services and turn vast archives into accessible tools. This scientific and technical foundation could support very different decisions.
Following migration through the night. Estimated bird densities across Europe at hourly intervals during the night of 3-4 October 2016. The sequence reveals a migration corridor from northern Germany towards south-western France and shows how rain over central and eastern Europe constrained movement.
Source: Nussbaumer et al. (2019).
When the forecast calls for darker skies
Artificial light can attract and disorient birds migrating at night. The risk is not constant, however. The volume of migration changes considerably from one evening to the next.
In New York City, GloBAM researchers worked with the New York City Bird Alliance and a broader Lights Out coalition to bring radar-based evidence into discussions on urban lighting. Advances in computing had made it possible to analyse and present migration at continental scales, while the city had become increasingly receptive to conservation measures. “Our research was at the right place at the right time, bolstered by technological advancements that allowed us to analyse and present data compellingly”, recalls GloBAM researcher Andrew Farnsworth.
New York City subsequently adopted two related laws. One restricted non-essential outdoor lighting in city-owned and certain city-leased buildings during the spring and autumn migration periods. The other introduced occupancy-sensor requirements to reduce unnecessary lighting in city-owned spaces.
The measures resulted from sustained work by a large coalition. For the researchers, the challenge was to make complex evidence persuasive without overstating it. “Capturing attention while maintaining scientific integrity was one of our biggest hurdles”, Farnsworth says. “We had to ensure our message was both impactful and grounded in data.”
Tracking migration across a continent. BirdCast uses weather-radar data to map nocturnal bird migration across the United States in near real time, showing where migration is most intense, how birds are moving and how many are estimated to be in flight.
Credit: BirdCast, live migration map, 4 May 2026, 01:10 ET. Cornell Lab of Ornithology.
Sharing the skies with aircraft
The same radar observations also had applications in aviation. Bird strikes pose risks to civilian and military aircraft, particularly during lower-altitude operations. GloBAM worked with aviation authorities, air forces and meteorological services to examine how radar-based migration information could support flight planning.
In the Netherlands, GloBAM built on a longstanding collaboration with the Royal Netherlands Air Force and the FlySafe Bird Avoidance Model, which provides migration information and warnings for military aviation. GloBAM researchers analysed nearly a decade of weather-radar observations to improve forecasts of migration intensity under different weather conditions.
The Finnish team developed a demonstration interface for bird-collision hazards and a migration forecast for Finnish airspace. In the United States, GloBAM research combined radar and citizen-science observations to study bird strikes at commercial airports.
The challenge was not simply to make forecasts more accurate. Migration forecasts inevitably carry uncertainty. Researchers and aviation partners therefore had to determine which information was still useful, how it should be presented and how quickly operators needed to receive it. Forecast skill mattered, but so did delivering the result in a form and timeframe they could use.
Turning radar observations into aviation warnings. This composite translates radar-detected concentrations of birds and insects over the Netherlands, Belgium and Germany into BIRDTAM values used in aviation. Higher values indicate greater aerial biomass in the lower airspace, while large black areas mainly represent rain. The information helps flight planners identify periods and areas of increased bird-strike risk.
Source: FlySafe Bird Avoidance Model.
Slowing turbines as birds cross the North Sea
Offshore wind energy posed a related problem, but required a different response. Large numbers of birds cross the North Sea at night during seasonal migration. Temporarily slowing turbines can reduce collision risks, but operators and electricity-grid managers need sufficient warning to prepare for a fall in energy production.
GloBAM researchers worked with Dutch authorities, meteorological services and wind-energy actors to identify the conditions associated with intense migration. Their discussions helped clarify the forecast lead times, thresholds and level of certainty needed to make temporary curtailment workable.
In May 2023, the Netherlands conducted its first large-scale test of slowing offshore wind turbines to allow migrating birds to pass more safely. The Start/Stop procedure came into force that July and has since been used during periods of mass migration. GloBAM’s Dutch partners contributed to the forecasting research and stakeholder collaboration on which the approach was built.
The resulting process involves more than a scientific forecast. It must also account for expert assessment, government decisions, wind-farm operations and the stability of the electricity grid. The contrast with aviation is instructive: flight planners may be able to use information delivered at relatively short notice, but curtailing offshore energy requires a longer lead time and coordination among several organisations. The underlying migration data may be similar, but the service built around it cannot be the same.
From migration forecast to turbine curtailment. The Dutch Start/Stop procedure combines a migration prediction with expert assessment, checks on electricity security of supply, a government decision and coordination with wind-farm operators. During expected peaks, turbines are slowed to near standstill before the results are inspected and evaluated.
Source: Dutch Ministry of Infrastructure and Water Management.
What made a difference?
GloBAM involved potential users from the beginning. Meteorological institutes helped frame the project and provided the radar data on which it depended. Aviation, energy and conservation stakeholders took part through national meetings and collaborations, helping researchers understand what information would be useful in practice.
The project also recognised that engagement worked differently in each country. National partners understood their own institutions, policies and languages and could reach the relevant users directly. This allowed each partner to translate the shared research into its national context. Open software, data formats and visualisations extended that reach by enabling others to reuse the work and develop new applications.
GloBAM began with information already hidden in weather-radar archives. It helped make those traces more consistent, accessible and timely, and connected them with decisions in the real world. Once migration could be seen in advance, different actors could respond: switch off lights, adjust flights or slow turbines.
From weather observations to biodiversity information. Grey lines show the established flow of European radar data for meteorological products; blue lines show the proposed pathway for biological applications. Because meteorological cleaning can remove echoes from birds, bats and insects, biodiversity monitoring requires access to uncleaned polar-volume data and dedicated processing.
Adapted from Shamoun-Baranes et al. (2022).
In brief
- Weather radars record more than rain. They also detect birds and insects moving through the atmosphere, often at night and beyond the reach of observers on the ground.
- GloBAM developed methods, data and forecasts that made these movements easier to monitor across Europe and North America. Its work supported action to reduce unnecessary lighting, improve aviation safety and slow offshore wind turbines during periods of intense migration.
- The project showed that useful forecasting is not only about predicting accurately. It also requires understanding who will use the information, what decision they need to make and how much warning they require.
Explore more impact stories
This summer, Biodiversa+ looks back at research projects supported through its predecessor, BiodivERsA, exploring how scientific collaboration has contributed to policy, practice and innovation. Each story highlights what changed, how researchers worked with stakeholders, and what future projects can learn from their experience.
