Conserving Verreaux's Eagles
In 2015 the Verreaux’s Eagle Aquila verreauxii conservation status was changed from Least Concern to Vulnerable in southern Africa due to decreases in range and abundance recorded by the South African Bird Atlas Project. Our project on this species initially focused on investigating the potential impacts of land use change and habitat loss in the Western Cape. Generally regarded as a highly specialised raptor, habitat transformation was predicted to reduce availability of its preferred prey species, the Rock Hyrax Procavia capensis, resulting in reduced breeding productivity or increased foraging effort. Contrary to this prediction, our research in the Cederberg and Sandveld regions of the Western Cape found that Verreaux’s Eagles were able to diversify their diet in agriculturally developed areas and found that their breeding productivity did not appear to be negatively affected by the levels of agricultural transformation currently experienced in the Sandveld region. A more recent and national threat is the development of wind farms, and efforts have now shifted toward modelling the potential impacts of wind developments on this species.
The demand for renewable power is increasing worldwide and the installed electricity generation from wind power is growing rapidly. In South Africa, there are now over 1,000 operational wind turbines across 22 wind farms. In addition, 112 renewables projects have been approved by the Renewable Energy Independent Power Producer Procurement Programme (REIPPP) to date. Thus the installed wind power capacity in South Africa can be expected to continue to rise rapidly. Wind energy is often regarded as a sustainable solution to our increasing energy demands. However, it is evident worldwide that there are negative impacts on birds through collisions with rotor blades. In South Africa post construction monitoring has found that diurnal raptors are the most frequently killed bird guild, representing around 35% of all casualties recorded. This disproportionate effect on raptors is extremely worrying and we are consequently working towards predictive collision risk models for the most at risk species. Verreaux’s Eagles are considered high risk due to multiple collisions that have already been sustained and their conservation status. This project aims to build a predictive mapping tool to enable turbine placement to occur in areas that will minimise the risk of collision for this species. To do this we are using high-resolution GPS tracking technology to understand flight behaviour, habitat use and the associated risk of wind turbine collisions. The aim is to produce an online collision risk model which can be used by the wind energy industry to obtain a collision risk map of any potential development areas early in the planning stage, thereby ensuring that wind turbines can be placed in locations that will minimise risk to flying eagles.
Activities in 2018
- Fieldwork during 2018 included ongoing monitoring of the GPS tagged Verreaux’s Eagles in the Karoo, Overberg and West Coast areas. Due to the large volume of data generated by the tags (over 1,000,000 fixes during 2018) data downloads are done via base stations (rather than directly via satellite). This requires frequent maintenance of remote field equipment.
- We worked with a number of 3rd year Computer Science students and their supervisor Dr Michelle Kuttel to build a prototype website that will allow developers to utilize our risk model for Verreaux’s Eagles in the development area.
- The tracking data set is now large enough to derive robust estimates of collision risk and thus the second version of the risk model was built using data from all 16 tagged eagles. This model was requested and used by wind farm developers in the Sutherland region of the Karoo. This confirmed the demand for such models. The final model will be available in 2019.
- We published a paper using our tracking data to examine when and where Verreaux’s Eagles use either thermal uplift or orographic lift for soaring titled ‘Where eagles soar: Fine‐resolution tracking reveals the spatiotemporal use of differential soaring modes in a large raptor’ in Ecology and Evolution.
Impact of the project
This project has added to our understanding of the ecology and habitat requirements of Verreaux’s Eagles. The primary aim of the ongoing work is to contribute to reducing future injuries and mortalities of Verreaux’s Eagles due to wind turbine collisions throughout their range. This will contribute to the long-term sustainability of wind energy development within Sub-Saharan Africa and will minimise the impact on one of the most widespread and vulnerable eagle species on the continent.
ABAX Foundation; DST-NRF CoE grant; BirdLife South Africa; Hawk Mountain Sanctuary; Mainstream Renewables; Avisense Consulting; Tygerberg Bird Club.
Dr Arjun Amar (FIAO, UCT)
Dr Megan Murgatroyd (FIAO, UCT)