About This Project

Ask the Scientists

What is the context of this research?

The Martial Eagles are broad-winged, tree-nesting raptors which are widely but sparsely distributed across Southern Africa. The IUCN red list has declared the eagle a Vulnerable species, as these eagles have declined nationally (according to recent bird atlas data, SABAP2 Data).

The Electric Martial Eagle Project will focus on Martial Eagles, which breed on the high voltage power lines within the commercial ranch-lands of the Karoo South Africa. This is an area which has received little survey coverage through the national SABAP surveys. These birds have adapted to breeding in this largely treeless environment by building their nests on electricity pylons. To date only 10% of the total transmission lines have been surveyed, yet this survey revealed nearly 60 breeding pairs and the total number of pylon-nesting pairs in this biome may therefore be quite substantial. This project will attempt to establish the true size of this population and will also investigate the diet of this population. This study will therefore determine whether we might be underestimating the species population size and also the potential nationally importance of this population. It would also suggest that the species may be significantly subsidised, rather than threatened, in this area by this specific form of development.

What is the significance of this project?

The number of pylon-nesting Martial Eagles pairs in the Karoo may be more substantial than bird atlas data suggests, perhaps even eclipsing the breeding population contained within the South African 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 vulnerable species, as well as a shift in the emphasis of associated research and management activities.

What are the goals of the project?

Funding for this project will go toward the field work for the Electric Martial Eagle project.

The previously surveyed Karoo power transmission line will be re-surveyed by helicopter in search of Martial Eagle nest (1). 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 use a green lining when their nest are active ( ie the nest will be used to raise chicks). It is also much easier to view chicks in the nest using helicopter surveys. These data are needed to determine whether nest are active or inactive and therefore will give an indication of population size.

A further ground and aerial survey of a sample of ‘new’ never before sampled power lines (approximately 1000km in the North in close proximity to Springbok) 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 will 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 (1).

Lastly helicopter and ground surveys will be conducted of a representative sample of drainage lines in close proximity to the Karoo transmission lines. These surveys will be searching for trees which would be able to support Martial Eagle nest. 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.

In addition to the surveys I will be looking at the diet of Martial Eagles. 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 (Bushnell motion sensitive camera traps) will be placed in 6 Martial Eagle nest. 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.