The Black Eagle Project
In South Africa the Verreaux’s eagle has been highlighted as a species of conservation concern and one that is particularly susceptible to collisions with wind turbines. Therefore, in 2016 a new project was initiated which is focusing on building a tool to predict space use of the Verreaux’s eagle to enable wind farms to be placed in areas that minimises their risks to this species.
The demand for energy is increasing worldwide and wind turbines are often considered as a viable option for ‘green’ energy production. However, concerns over the impacts on bird populations are increasing, as collisions with blades and displacement from home ranges have become evident. Of particular concern is the negative impact that raptor populations have sustained. Raptors are long lived and reproduce slowly. Therefore, even apparently small increases in mortality rates can be problematic for their local populations.
Predictive modelling has proven useful for other raptors for early identification of core use and high collision risk areas inside development plans. This project aims to collect fine-scale information on the flight behaviour of this species by tracking individuals with high-resolution GPS tags. The tags will record information including flight altitude, location, trajectory and speed at frequent intervals. Data will be analysed to explore how territory holding eagles use the landscape, in particular how this relates to the distances from the nest, topographical features and collision risk. Using these results we will be able to build habitat use models that are generalizable across the distributional range of the species.
These models will be incorporated within a novel user-friendly web based interface for use by the wind energy industry. This will allow developers to simply use the location of the species nest sites (which is collected as standard during pre-construction environmental impact assessments) to obtain a relative collision risk map of the area – thereby ensuring that wind turbines can be placed in locations that will minimise risk to flying eagles. This will contribute to the long-term sustainability of wind development within Sub-Saharan Africa and minimise the impact on one of the most widespread eagle species on the continent.
The Black Eagle Project History
The Black Eagle Project began in 2011 when Megan Murgatroyd first registered as an MSc student at the University of Cape Town. The initial aim was to research the impacts of agricultural transformation on the ‘Black’ or officially, the Verreaux’s eagle.
The study was designed to compare the breeding performance and diet of eagles in the relatively pristine Cederberg Mountains with those inhabiting the nearby Sandveld region. The Sandveld has an incredibly rich flora and fauna, but has been subject to widespread habitat loss through agricultural transformation, largely for the potato industry. While the Cederberg offers abundant cliffs suitable for Verreaux’s eagle nest sites, the Sandveld is relatively flat. However, rocky outcrops and ‘koppies’ in the Sandveld provide suitable nesting substrate.
After one year of research it quickly became evident there was a large difference in the breeding performance of these two eagle populations. However, it was not as expected: In 2011 Verreaux’s eagles in the Sandveld produced 0.75 young per pair, while in the Cederberg only 0.46 young were fledged per pair. This finding was contrary to the hypotheses that were formed at the outset of the project based on evidence that agricultural transformation often has a negative effect of biodiversity. Intrigued, Megan was now in it for the long run and was accepted for an upgrade to PhD.
Megan’s PhD thesis compiled 4 years (2011-2014) of breeding productivity data, diet analyses and high-resolution GPS tracking data. This allowed a comprehensive understanding of the effects of agricultural transformation on this species.
In brief, this research found that average breeding productivity was considerably higher in the Sandveld (0.76 ±0.05 young per pair) than the Cederberg (0.28 ±0.13 young per pair). This was in part due to higher rainfall during the chick rearing phase in the Cederberg than the Sandveld, which negatively impacted on chick survival. However, a much smaller proportion of the population made a breeding attempt in the Cederberg than the Sandveld every year and this could not be contributed to any of the environmental variables tested. Verreaux’s eagles have long been thought of specialist predators of rock hyrax. Diet studies in the Cederberg found that the diet of resident eagles is made up of c. 98% rock hyrax. However, in the Sandveld hyrax make up just c. 25% of the diet. Mole-rat and angulate tortoise contribute a significant proportion of the other species consumed. Within the Sandveld, this increased variety of prey does not appear to negatively impact on breeding productivity, demonstrating that Verreaux’s eagles are less specialized than previously assumed.
GPS data collected from eagles in both regions also supported these findings. Unlike other species, which have had to travel further of hunt for longer periods of time to attain all of their nutritional requirements in human-altered habitats, eagles in the Sandveld did not appear to move differently from those in the Cederberg.
Contrasts in the uplift availability between the study areas were also revealed by analyses of high-resolution GPS data. GPS data were used to identify areas where eagles were gaining flight altitude by orographic and thermal lift. Using this information, Megan was able to predict the spatio-temporal uplift availability in the landscape. Although these findings were based on a small sample size, they indicated that it is likely that Verreaux’s eagles in the Sandveld can benefit from a greater availability of thermal lift compared to in the Cederberg.
All of these factors combined have allowed for Verreaux's eagles to thrive in a relatively transformed agricultural landscape. Although there is likely to be a threshold level of transformation that this apex predator can cope with, it appears to benefit from a mixed heterogeneous environment.
To find out more check out the links on our publications page.