During the summer of 2008, AGE OOD (AGE), developer of the Saint Nikola Wind Farm (the Project), was made aware that winter bird survey records for the region, during 2007/2008, had shown what appeared to be potentially significant winter flight activity in the general area of the proposed development. Of particular interest was the reported presence of the Red-breasted Goose (RBG), a globally threatened species. Recognising the importance of RBG in particular, as part of the ongoing works and environmental commitments associated with the Project, AGE undertook to carry out bird surveys during the 2008/2009 winter season, prior to operation of the Project. The survey resulted in the first estimation of the number of geese flying through the wind park territory and a Collision Risk Model predicting potential RBG mortality as a result of colliding with operating turbine blades. As a result it was proposed to have a second winter season survey during the post construction and operation of the wind park with the application of the radar provided in line with EMMP and requirements of Bulgarian Ministry of Environment and Waters.
The following main goals were set for the 2009/2010 survey:
- Record winter bird activity specific to the Project area (the 2008/2009 survey highlighted potential activity in the region, but the data were not sufficient with respect to Collision Risk Assessment Model);
- Ascertain whether there is potential for the constructed already wind park to have a significant adverse effect on the wintering birds (with a particular focus on RBG);
- In the event that a significant adverse effect was predicted, what mitigation measures would be required to reduce the effect to an acceptable level.
The wintering period of the geese in the region started in the middle of December 2009 (early January in the Project area) and ceased by the end of February 2010. Greater White-fronted Goose (GWFG) was the most common species recorded, and the percentage occurrence of RBG in goose flocks was about 10 %. Greylag Goose was recorded sporadically and in small numbers and was not therefore considered at risk from the project. Lesser White-fronted goose was not recorded. The duration of the winter stay in the study area was similar for both RBG and GWFG with a concentration of over 90% of RBG being seen within 20 days, corresponding to the coldest period of the winter. These results were similar to those from the 2008/2009 winter.
The flight altitudes of the geese from all species observed crossing the Project area were most intensive between 50 and 100 m above ground level. Flight activity of geese was greatest in the morning (7-9h) and, to a lesser extent, evening (16-18h). These findings were also similar in the 2008/2009 winter.
The results of the Collision Risk Assessment in 2008/2009 was based on an assumption of over 65,000 flights of RBG through the Project area and predicted 22 RBG collisions per year, applying a precautionary 99% avoidance rate. This prediction fell short of the threshold number of collisions (31) that would need to occur to result in a significant impact. While the threshold criterion is flawed and requires replacement with a more appropriate alternative, in the interim it follows the EMMP.
The number of RBG flights (30,500 flights detected by the radar) during the 2009/2010 winter, when used in a Collision Risk Assessment, predicted 1 – 9 RBG annual collisions (the range given by different assumed avoidance rates). This result suggests that the Project does not have the potential to have an adverse impact upon the RBG population.
A contributory explanatory factor to the differing predictions between the two winters, despite several other similarities, is likely to be the improved survey methods employed in the 2009/2010 winter study. Use of the Black Sea as a roost site by geese had been previously suggested as a factor that could increase collision risk, but the 2009/2010 results suggest that this is not the case.
Further refinements will be possible once monitoring of collision victims occurs in the 2010/2011 winter and in bringing in results from the study of GWFG as well as RBG.