The present monitoring study was conducted after the issuing of an environmental authorisation for the project, with the primary objective of refining the findings of the original avian impact assessment, chiefly by generating a quantified and spatially explicit understanding of the avifauna present on and around the proposed development site, identifying any definable flight lines and/or key resource areas used routinely by birds in the area, an) using the outcomes of and to draw up a more informed assessment of likely impacts of the project, and a more explicit set of recommendations to manage and mitigate these impacts.
The study was designed and conducted explicitly in terms of the BirdLife South Africa / Endangered Wildlife Trust guidelines for bird monitoring at proposed wind farm sites in South Africa. Teams of two observers visited the study area for 3-5 days at a time on five occasions spread over a 12- month monitoring period from July 2011 to June 2012, accumulating 40 person-days on site, and amassing 1195 sightings describing the location, behavior and movements of 3599 individual birds of 117 species.
The broader study included the collection of comparable data from a nearby and similar control or reference area in order to establish a benchmark against which to measure the actual impacts of the wind energy project post-construction. In addition to this observer-based work, radar-based monitoring was conducted at both the proposed development site and the control from late June to mid-December 2012, with the primary aim of determining the extent, nature and patterns of nocturnal movements by birds through the affected area.
Walked transect data revealed that the small terrestrial bird populations of the study area and the control site were comparable, yielding overall densities 2.34 vs 2.16 birds.ha-1 respectively. Driven counts of large terrestrial birds and raptors registered peaks in the abundance of these birds in and around the proposed development area in winter and spring, largely the result of quite strong seasonality in numbers of the red-listed endemic Blue Crane Anthropoides paradiseus. Wetland counts showed that numbers of waterbirds were quite low and erratic.
Over 180 hrs of diurnal bird movement data were accumulated at vantage points in the two areas, yielding comparable average passage rates of day-flying birds (8.39 birds.hr-1 in the study area, 6.75 birds.hr-1 in the control). A short-list of red-listed and/or endemic and/or ecologically significant priority species made up < 7% of the vantage point records from the study area, with the most frequently counted species being Blue Crane. Rough estimates of annual turbine collision rates for diurnally flying birds at the West Coast One site include figures of nearly 500 birds overall, but only 12 casualties of priority species, comprising nine Blue Cranes, two Lanner Falcons and one Black Harrier.
Most groups of birds were relatively unpredictable in their patterns of diurnal movement through the proposed development area. However, Kelp Gulls regularly used a flight-line in the north-east of the site during the day, perhaps indicating that this corridor may also be used occasionally by other commuting coastal or wetland species, and suggesting a need to either re-locate five turbines in that West Coast One Wind Energy Facility – Avian risk & mitigation 4 area (and particularly turbines 4 and 5), or to strategically control the operation of these turbines in relation to time of year, time of day and wind direction. An initial draft of a separate report on radar-detected nocturnal flights through the study area shows that there is considerable avian activity in and around the site overnight.
Clarity on the seasonal, temporal and taxonomic breakdown of this activity requires further, more detailed analysis of the large dataset obtained during the sampling period. However, even early spatial analyses show that the north-east fly-way is also used extensively by birds moving through the area at night, confirming the need to take strong action to mitigate the possible impacts of turbines placed on or close to this flight-line.
Comprehensive post-construction monitoring, and a preparedness to make meaningful changes to the project in the event that high levels of displacement or mortality of priority bird species are detected, will be essential to ensure that the avian impacts of this proposed wind farm are kept to a sustainable minimum.