The Electric Martial Eagle Project

The Electric Martial Eagle Project was initiated by Jessie Berndt in 2013. She is a Masters by Dissertation student with the Percy FitzPatrick Institute of African Ornithology at the University of Cape Town. Her project is focused on Martial Eagles which nest on steel lattice pylons supporting highvoltage power lines in the commercial ranch-land of the Karoo region. This project is under the supervision of Dr Andrew Jenkins, Associate Professor Res Altwegg and Dr Arjun Amar at the University of Cape Town, Percy FitzPatrick Institute.

 

Project aims

• To establish the true size of this population of Martial Eagles which nest on steel lattice pylons supporting high voltage power lines in the commercial ranch-land of the Karoo region.
• To assess whether the incidence of pylon-nesting in Martial Eagles is inversely correlated with the availability of suitable nesting trees and whether pairs nesting on transmission line structures in essentially tree-less environments represent artificial extensions of the species’ range.
   
• Determine whether conventional bird atlas data serves adequately as an index of abundance for large, scarce birds in relatively remote environments, such as Martial Eagles in the Karoo.
   
• Assess Martial Eagle diet in relation to Land use activities

This information will contribute towards clarifying the true status of the Martial Eagle in South Africa. The population status of Martial Eagles which nest on steel lattice pylons supporting highvoltage power lines will motivate strongly for a corresponding adjustment in South African perspectives on the conservation biology of this globally vulnerable species (www.iucnredlist.org), as well as a shift in the emphasis of associated research and management activities.

Background

The Martial Eagle,Polemaetusbellicosusis a large, broad-winged, tree-nesting raptor which is widely but sparsely distributed across Southern Africa (Simmons 2005). The South African population is currently estimated at <600 breeding pairs (Barnes 2000), with breeding densities reputed to be much lower outside of the larger protected areas (Barnes 2000, Simmons 2005). This alleged confinement to conservation areas suggests a heavy dependence on pristine habitat, a notion endorsed by recent bird atlas data describing a significant decrease in the aggregate range of the Martial Eagle in South Africa, and a corresponding decline in relative abundance throughout much of its remaining distribution, particularly outside of protected areas, but even within the Kruger National Park (Underhill 2012). However, an apparently stable population of 60 pairs of Martial Eagles which nests on man-made structures in commercial ranch-land of the Karoo region (Dean 1975, Boshoff 1993, Machange et al. 2005, Jenkins et al.2013) could indicate more resilience, and a greater level of adaptability, in this species than is generally believed.

Photo by Koos De Goede

The eagles in question build nests in steel lattice pylons supporting high voltage power lines running through a largely tree-less, semi-arid landscape, and may even be quite recent colonists of large areas of the Karoo, on the back of the still expanding power transmission network (Dean 1975, Boshoff 1993). Equally significantly, the length of power line surveyed to date in documenting this substantial population constitutes <10% of the transmission power line available to Martial Eagles in the Karoo (Jenkins et al. 2011, 2013), so the total number of pylon-nesting pairs in this biome may well be even more substantial, perhaps even eclipsing the breeding population contained within the country’s nature reserves. Should this be so, it would motivate strongly for a corresponding adjustment in South African perspectives on the conservation biology of this globally and nationally ‘vulnerable’ species (www.iucnredlist.org, Barnes 2000), as well as a shift in the emphasis of associated research and management activities.

Photo by Koos De Goede

How would a scientist estimate the population size of Martial Eagles in the Karoo?

The previously surveyed Karoo power transmission line will be re-surveyed (see study site for details) by helicopter in search of Martial Eagle nests. This is 1400 km of 400kV electricity transmission pylon line, extending from Koeberg in the southwest, to Kenhardt in the north and De Aar in the east. These surveys have to be done by helicopter, because eagles nest high on top of the pylons making it almost impossible to see a breeding bird, eggs, small chicks or the green lining used by eagles when their nest are active ( i.e. the nest will be used to raise chicks). Helicopters are able to hover which provides us with the opportunity to determine the status of any nest. These data are needed to determine whether nests are active or inactive and therefore give an indication of the breeding Martial Eagle population size. 

In addition aerial surveys of a sample of ‘new’ never before sampled power lines approximately 2500km would have to be helicopter surveyed too. These new survey data will be used to verify a habitat association model (a model which basically predicts where Martial Eagles are likely to nest on the power lines in relation to environmental variables such as rainfall, topography, productivity, land use and vegetation structure), which I will build with the survey data from form the 1400km of 400kV power line.

How do you assess whether Eagles have been drawn in from the surrounding habitat to nest on pylons?

During these helicopter surveys we will deviate from the power transmission network in search of Martial Eagle nests in trees in close proximity to the transmission network. The assessment of the extent to which Martial Eagles are drawn from the surrounding areas to use pylon structures by estimating nest densities in proximity to drainage lines ( in trees) will give an indication of whether these eagles are recent colonists of essentially tree-less habitat ( The Karoo), stemming directly from the expansion of the power transmission network in the Karoo. This survey will give insight into the secret life of pylon nesting eagles and why pylon nesting is common in the Karoo.

 

Photo by Chris Laidler

How do you assess the diet of an eagle?

Martial Eagle diet will be assessed to determine if it is affected by land use practices. Access to an adequate prey base will play a significant role in determining the presence, absence and success of breeding pairs of eagles. Nest cameras will be placed in 6 Martial Eagle nests. The primary use for these is to determine what prey being is brought to the nest to feed chicks. The motion sensitive camera diet data will be related to prey remains found beneath the nest (this requires a lot of driving to acquire samples), land use and vegetation in the Karoo. These data allow me to track dietary changes displayed by Martial Eagles due to land use.This will help us determine how sensitive Martial Eagles are to environmental modifications caused by land use practices.

Photo by Chris Laidler- Jessie collecting prey remains