Divers are a group of piscivorous aquatic birds which breed on lakes in the tundra and taiga zones of the Holarctic region. Their ecology is water-bound. Divers are excellent swimmers and dive to ten meters and more when feeding but are poorly adapted to move on land. In the German Bight the two diver species Black- and Red-throated Divers occur in large numbers during wintering.
Offshore windfarm development is increasing in this area which can lead to conflicts as divers are very sensitive to anthropogenic disturbance. Within this study we are catching divers in the German Bight and implant satellite transmitters aiming to understand movement patterns of these birds during the wintering season and during their migration. Further the interactions between divers and offshore windfarms are studied as well. Habitat use, connectivity of resting areas, locations of origin plus migration patterns can be determined by analyzing the tracking data.
Project duration: 01.11.2014 – 30.10.2018.
Development of offshore windfarms is an important element towards expanding the share of renewable energy in Germany. And this development aims not only to provide clean energy but also to prevent and minimize possible impacts on the marine ecosystem.
Wintering seabirds are an important part of the marine ecosystem but react sensitively to anthropogenic structures and urbanized estuaries. Many of them have wide distribution ranges and utilize different habitats and therefore also occur outside the protected areas and could be affected by anthropogenic activities. As a result conflicts cannot be ruled out using current knowledge.
Divers belong to the Family Gaviidae, divided in five species, Great Northern Diver (Gavia immer), White-billed Diver (Gavia adamsii), Pacific Diver (Gavia pacifica), Black-throated Diver (Gavia arctica) and Red-throated Diver (Gavia stellata), of which only the latter two species occur in relevant numbers in the German Bight. Diver wintering distribution in Europe extends along the coasts of the North Sea, the Baltic Sea and the northern Mediterranean. It is believed that the breeding distribution of these birds covers an area including Russia, the Scandinavian Peninsula, Great Britain, Iceland and Greenland. However, not much is proven about locations of origin because recoveries of ringed birds are very rare. In the offshore areas of the North Sea divers occur in internationally important numbers during wintering period, using a wide range of areas and being highly mobile within them, but are known as being very sensitive to disturbance. They also occur in great numbers in, or close to areas which are used by fisheries, or planned for offshore windfarms, but knowledge about the impacts of these anthropogenic structures on divers is limited.
Investigations at the existing offshore windfarms have led to the suggestion that there is a potential for conflicts between the windfarms and both diver species occurring in the North Sea, the Red-throated Diver and Black-throated Diver. These species are known to be very sensitive to disturbance and as a consequence show a significant avoidance reaction (e.g. Petersen et al. 2006, Dewar 2011, Dierschke et al. 2012, Petersen et al. 2014). Divers use areas with a wide range of water depths and occur in the North Sea in areas with water depths up to 40 meters (Mendel et al. 2008, Petersen & Nielsen 2011). Due to their mobility during the wintering season divers can be affected cumulatively by several offshore windfarm projects (Mendel et al. 2008, Leopold et al. 2011). To evaluate the interactions and impacts between offshore windfarms and divers, information about the following aspects is essential:
• Habitat use during wintering season, especially size of home ranges and residence time
• Connectivity between different resting areas/ stop over sites
• Identification of breeding areas to establish which populations can be affected
Systematic investigations concerning these species are essential to fill the knowledge gaps and to improve and facilitate the process of decision making regarding current and future action of offshore windfarm planning in proximity to important diver habitats.
The research project DIVER has been initiated aiming to determine the interactions between divers and anthropogenic structures. State of the art telemetry methods are used to collect data about diver habitat use and mobility patterns during the wintering season in the North Sea as well as localization of breeding areas and migration routes. It is planned to equip 45 divers with satellite transmitters during 3 winter seasons. Birds will be captured in the North Sea during the wintering season and their movements are expected to be tracked for at least one year. Argos satellite transmitters provide positions with an accuracy of a few hundred meters, which represent sufficient accuracy for analyzing bird movements within as well as between different habitats during the course of the year. Additionally bird fecal and blood samples are taken for nutrition analysis, and blood samples are also used for determination of gender. In Europe similar studies on pelagic living seabirds like divers are rare. Hence the results of this project are expected to fill several knowledge gaps about habitat use and movements of divers and will help to develop and improve conservation plans for these species.
As a Joint Venture between BioConsult SH, Justus Liebig University of Gießen (Department Animal Ecology and Systematics, Research Group Behavioural Ecology and Ecophysiology) and DHI, the project follows the overall objective to fill the knowledge gaps regarding ecology of divers, e.g. habitat use and movement patterns within critical areas aiming to support conservation plans for this species as well as to improve conditions for developing conservation tools and actions for this species. Considering offshore windfarm developments, spatial distribution and temporal characteristics of habitat use of divers will be analyzed to set a sound basis for the relation of habitat loss due to offshore windfarms and habitat requirements of divers. Following knowledge gaps were identified:
- Little is known about habitat use and movements of divers within and between different wintering areas. It has been suggested that diver habitat choice varies in relation to tidal currents, other hydrological changes and direct weather impacts.
- Migration patterns and general movement schedules throughout the annual cycle of divers are largely unknown. Diver numbers fluctuate substantially in different wintering areas and intensive movements have been recorded along the coasts of the Baltic and North Sea. This indicates high mobility during the non-breeding period. As a result of the knowledge gaps about migration and local patterns, it has not been possible to understand and to evaluate the cumulative impacts of different human activities on these birds.
- Site fidelity to wintering and other staging areas is unknown. Whether birds are highly site faithful and return to the same places year after year or are flexible in using different geographic areas has important implications in evaluating potential impacts on populations.
- Locations of origin are unknown. During the non-breeding period divers are widely dispersed along the coasts and offshore areas in the Baltic and North Seas and northern Atlantic. Breeding populations are distributed across high latitudes of Russia, Scandinavian Peninsula, UK, Iceland and Greenland. Recoveries of ringed birds are scarce and therefore it is unknown which breeding populations are being affected on wintering and staging grounds.