Short-Term Behavioural Responses of Wintering Waterbirds to Marine Activity: Quantifying the Sensitivity of Waterbird Species during the Non-Breeding Season to Marine Activities in Orkney and the Western Isles
Scottish Marine and Freshwater Science Vol 9 No 7
1. Waterbirds are subject to a range of pressures on their wintering grounds, with disturbance and pollution being potentially the most significant. In the British Isles, significant populations of waterbirds winter in the seas including around Orkney and the Western Isles. 2. Increased marine activity associated with exploitation of the abundant wind, wave and tidal resources around Orkney and the Western Isles, in addition to increased aquaculture activity and existing shipping and shellfishing activity, has the potential to negatively impact wintering waterbird populations through increased disturbance. 3. The scope of this research project was to compare the relative sensitivities to marine activity of eleven target waterbird species during the non-breeding season. This was achieved by gathering data during a single winter fieldwork season on Orkney. 4. The research was focused on the following species: Common Eider, Long-tailed Duck, Velvet Scoter, Common Goldeneye, Red-breasted Merganser, Red-throated Diver, Black-throated Diver, Great Northern Diver, European Shag, Slavonian Grebe and Black Guillemot. 5. Data were collected using three complementary survey methodologies: Vantage Point (VPs) surveys, focal flock watches and ferry surveys. The methods were designed to gather systematic data on the target species’ short term behavioural responses to marine activity, and environmental variables considered likely to affect those responses. 6. The VP surveys indicated that Common Eider, Long-tailed Duck and European Shag were all significantly more likely to fly in the presence of marine activity. The numbers of Common Eider, Long-tailed Duck, European Shag and Great Northern Diver within a pre-defined study area all declined following marine activity, whereas Black Guillemot numbers appeared unaffected. 7. The focal flock watch methodology involved recording the behaviour of target species flocks in the presence and absence of marine activity. Long-tailed Duck flock size was likely to decrease in the five minute period following a disturbance event, and this species was also the most frequently recorded flying in the absence of marine activity. Great Northern Diver and Black-throated Diver were very unlikely to fly either in the presence or absence of marine activity. 8. The ferry survey methodology involved gathering data on regular island ferry services and recorded target species’ responses to the passing ferry. Red-throated Diver, Black-throated Diver and Slavonian Grebe were the most likely species to exhibit a response (flight, evasive swim, or dive) to the passing ferry, and Red-throated Diver was most likely to show a flight response. 9. Whilst data were successfully gathered for nine of the target species across the three survey methodologies, too few data were collected for Common Goldeneye and Velvet Scoter to be able to draw conclusions. 10. Combining data gathered across the three methodologies, we categorised the sensitivity of nine target species (excluding Velvet Scoter and Common Goldeneye) as follows: very high (Red-throated Diver, Black-throated Diver, Slavonian Grebe and Red-breasted Merganser); high (Long tailed Duck and Great Northern Diver); medium (Common Eider and European Shag) and low (Black Guillemot). These sensitivities are assessed only in relation to the other target species, and are based solely on the data on short-term responses to marine activity gathered during this project. 11. Prior to this research little information on sensitivity to disturbance was in the public domain for Great Northern Diver, Slavonian Grebe and Black-throated Diver. The results presented here address important knowledge gaps which will help inform the marine planning process. 12. Gathering robust data on the effect of marine disturbance on waterbirds is challenging. Whichever methodological approach is followed there are likely to be significant practical challenges in data collection and analyses, and limitations on the conclusions which can be drawn. Furthermore, the spatial and temporal scales at which data is collected and analysed can significantly influence the results obtained. 13. Although all the fieldwork took place in Orkney, it is likely that the findings presented here are also applicable to the Western Isles. However we would advise against conclusions made here being applied to the larger estuarine ports of mainland Britain, where marine activity is likely to be of a different scale and intensity. 14. It should be borne in mind that the results and assessments presented in this report are based on short-term behavioural responses. Research is needed to better understand the mechanisms by which short-term behavioural responses might translate into demographic effects and the relative significance of the disturbance effects on habitat loss and energetic expenditure should be considered. 15. Recommendations for future research include suggestions to carry out a before-after-gradient study on the effect of new marine developments to assess long-term displacement effects, tracking studies of waterbird use of the marine environment in relation to marine activity, and trial disturbance tests using chartered boats.