Abstract
Around Europe, large-scale deployment of offshore wind is already well underway and is forecast to continue until at least 2020. However, uncertainties around the impacts of offshore wind on the environment, particularly marine birds, increase consent risk for future developments. Offshore wind farms are known to cause displacement of wintering red-throated divers (Gavia stellata), resulting in increased consent risk for projects planned for areas of high diver density. However, the consequences of this displacement at the individual and population level are unknown. Displacement is likely to increase energetic costs for divers but their ability to cope with these additional costs will depend on how energetically constrained they are. For the first time, energetics of red-throated divers is being investigated by the Red-throated Diver Energetics Project. Using time depth recorders and geolocators attached to red-throated divers on their breeding grounds, novel information on foraging behaviour of divers will be obtained.
Divers are sensitive to disturbance and are a difficult species to work with, but the experience and expertise of ringers ensured all tags were successfully deployed. During the summer of 2018, a total of 74 red-throated divers were tagged. Breeding birds were caught either using a nest trap or a wader net. All birds were fitted with two tags, a time depth recorder and a geolocator tag, as well as a metal ring with a unique number. Altogether, 31 red-throated divers were tagged in southern Finland, 31 in Scotland and 12 in Iceland. In Iceland and Finland, approximately equal numbers of males and females were tagged, whereas there was a slight bias towards tagging females in Scotland. Sex was assigned according to biometrics.
Red-throated divers had a poor breeding season in the Northern Isles, Scotland, with an average of 38% of nesting attempts producing a well grown chick, close to fledging. By contrast, 62% of nests in Finland fledged at least one chick. Given the sensitivity of divers to disturbance and the poor breeding season in Scotland, it was important to check that trapping divers did not affect their breeding success. Reassuringly, a comparison of breeding success for red-throated diver nests at which trapping of divers occurred and control nests with no trapping, showed no discernible effect of trapping on breeding success, in both Scotland and Finland.
Tagged divers will be recaptured in 2019, tags removed and data downloaded and analysed. Additionally, breeding success and other data will be collected at nests where trapping occurs and at control sites, to investigate any effects on divers from carrying tags for a year and/or a second season of trapping. Analyses of data retrieved from the tags will reveal dive frequency, depth and duration for red-throated divers, enabling assessment of the proportion of time divers spend foraging throughout the year. Periods when divers spend longest foraging will indicate when they are most energetically challenged. This information will provide key evidence to understand the time of year when divers are least able to cope with additional energetic costs, which will provide insight into the potential consequences of displacing wintering red-throated divers.