Maja Bradarić summarises how, alongside colleagues, they used 5 years of tracking bird radar data, weather and phenological variables to develop seasonal forecasts of bird migration over the southern North Sea. These forecasts of nocturnal bird migration may be used to define curtailment thresholds for offshore wind energy.
In May 2023, turbines in two offshore wind farms in the Dutch North Sea came to a virtual halt to allow safe passage for migratory birds during intense migration, marking an “international first” turbine curtailment of this scale. Since then, on-demand curtailments in Dutch offshore wind farms have been performed whenever intense bird migration was predicted across the southern North Sea.
Here, I write about how it all started, the research I conducted with my colleagues at the University of Amsterdam, and my experience of working with different stakeholders to help create a conservation protocol that can minimize the negative impacts of wind turbines on migratory birds while balancing energy production.
Balancing wind energy and wildlife
When the Netherlands made the ambitious decision to decuple its offshore wind energy production in the North Sea by 2050 to reduce CO2 emissions, it was clear that this would not come without cost for wildlife. The Dutch government, recognising the importance of bird conservation, introduced mandatory offshore wind turbine curtailments during intense bird migration.
This proactive approach was a response to a growing number of studies demonstrating various direct and indirect adverse effects of bird-turbine collisions on already declining bird populations and aimed to minimise collision risk and barrier effect that a growing number of turbines can cause for migratory birds.
Predicting bird migration
From the beginning, it was clear that the curtailment moments would need to be predicted at least 48 hours in advance to allow enough time for the energy grid operators to prepare for turbine shutdowns of such scale and make necessary adjustments. Therefore, my colleagues and I needed to think about developing a model that could predict bird migration intensity in advance. Many studies conducted across the globe showed that weather conditions could drive birds’ migratory departure decisions and, therefore, migration intensity in various ways. Over the North Sea, this was not well-explored, so we set off to shed some light on it.
To assess the migration patterns in the area, several bird-tracking radars were deployed at different wind farms. Radars can continuously record everything that passes through their range, making them an excellent choice for capturing dynamics in migration intensity. Over the years of research, we were able to infer the potential departure locations of birds we see on our radars, assess their numbers, altitudes and directions, as well as the main environmental factors that drive birds’ migratory movements.
We noticed that during both spring and autumn, the most intense migration occurs at night. During these intense migration nights, high-pressure weather systems represented by supportive, gentle winds and no rain pass through the area, prompting many birds to depart on their migration. The fact that weather is one of the main drivers of migration intensity over the North Sea allowed us to create models that use weather forecasts 48 hours in advance to predict migration intensity in the area.
Implementing conservation: Dynamic approach and various stakeholders
The models are now used in a curtailment framework coordinated by the Dutch government and developed by various stakeholders, including us as researchers, government representatives, energy grid managers, wind energy companies, ecological consultants, and non-governmental organisations concerned with bird conservation. At the moment, whenever the model predicts migration intensity above a certain intensity threshold, different steps described in the schema above are set in motion before a decision for curtailment is made by the Dutch Minister for Climate and Energy Policy.
From the beginning, this research project differed from most because of the constant communication between various stakeholders. There were instances when this was challenging, and we needed to be creative about communicating our respective expertise to each other. For me, as a scientist, this was exciting because it made me step out of my academic bubble, look at the questions I am working on from many different perspectives, and incorporate those perspectives into my research. While not easy, this interdisciplinary approach and knowledge exchange were, in my opinion, the main reasons why we managed to pull off a conservation measure of such scale and are a key for successful environmental management.
Although the curtailment procedure is now in place, this is only the beginning of conservation efforts. Independent evaluations of the model performance and curtailment procedure are done after each migration season, and the same group of stakeholders discusses where the improvements can be made. Models will be refitted with new data regularly, and the latest research is looking into how to adapt them for different regions in the North Sea basin to improve their accuracy further. With this, conservation can take place now while the steps taken are further being evaluated and improved “on the go”. Given the scale and pace of environmental alteration we are witnessing today, we aim to inspire more dynamic approaches to conservation through this example.
Read the full article “Forecasting nocturnal bird migration for dynamic aeroconservation: The value of short-term datasets” in Journal of Applied Ecology.
