Red-throated divers overwinter in relatively shallow and heavily impacted coastal waters of the North Sea and the Baltic Sea. Previous studies have shown that the species is highly sensitive to disturbance and often avoids offshore wind farms over large areas.
However, it was unclear whether this displacement merely leads to spatial shifts or whether it also affects foraging behaviour, activity patterns, energy expenditure and, consequently, the local population in the long term. The DiverLog project addressed this question, and its final report is now available.
The aim of the project was to record the individual behavioural patterns of red-throated divers more accurately than in previous studies, using modern GPS loggers. Between 2022 and 2024, a total of 68 red-throated divers were captured in the eastern German Bight in spring and fitted with transmitters that recorded the birds’ position data and, in some cases, their diving activity.
The study therefore provides the first detailed investigation of the foraging behaviour of red-throated divers in an offshore habitat outside the breeding season. It found that the birds spent an average of just 2.3 hours per day foraging.
Overall, the activity budget analysis showed that flight behaviour – and consequently energy expenditure – increased slightly when the birds approached offshore wind farms.
Data on habitat use, diving behaviour, time-activity budgets and energy expenditure were subsequently integrated into an individual-based model (IBM). This model was used to investigate the energetic effects of offshore wind farms on the physical condition of red-throated divers.
The results of the IBM showed a slight negative effect of offshore wind farms on the average body weight of red-throated divers. The ecological relevance of this change, particularly with regard to possible effects at population level, remains the subject of further investigation.
The results underline the importance of marine spatial planning: when planning offshore wind farms, key diver habitats should be avoided wherever possible. Where this is not entirely possible, the regulation of wind farm-related vessel traffic plays a particularly important role.
The authors of the study also propose long-term aerial monitoring of divers to investigate and document potential future changes in the birds’ behaviour in relation to wind farms.
Further information can be found in our project description.
