The Black Eagle Project
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.
