This project aims to understand the factors driving a decrease in the population of Martial Eagles Polemaetus bellicosus in South Africa, with a particular focus on the declines observed within the country’s largest protected area, the Kruger National Park. This research is important to understand the role of protected areas for conserving wide-ranging species and to understand specific threats and habitat requirements for the conservation of Martial Eagles.

This project was initiated in response to the decrease in reporting rates of Martial Eagles between the Southern African Bird Atlas Project, SABAP1 (1987-1992) and SABAP2 (2007-ongoing), which suggests a population decrease of up to 65% across South Africa. Declines were also observed inside large protected areas, such as the Kruger National Park (KNP), which experienced a 54% decrease in reporting rate. Similar decreases have been reported elsewhere in Africa resulting in the species being uplisted to ‘Endangered’ on the IUCN Red List.

We aim to improve our understanding of the threats faced by Martial Eagles and how these threats may drive population decreases even within protected areas. Our original hypothesis for these declines was that Martial Eagles may be subject to increased mortality outside of protected areas, particularly during immature life stages when inexperienced eagles are likely to range widely. Contrary to this hypothesis, we found little evidence for low survival during these early life stages, despite immature eagles ranging far beyond protected area boundaries. However, results from GPS tracking of adult birds and nest monitoring suggested two potential factors that may contribute to the observed population decreases: low adult survival and poor breeding productivity. Adult mortalities, including persecution and electrocution, during unexpected wide-ranging movements outside of the KNP, may be contributing to population decreases.

Nest monitoring indicates that two factors contribute to the low breeding productivity: a low proportion of pairs attempting to breed and low breeding success. However, due to the vast nature of KNP and difficulty in detecting all nests, using GPS tracking we have recently found that breeding performance may be better than initially thought. For several years we have been placing cameras at nests to better understand the factors that influence prey provisioning rates and diet.

Although we are no longer actively monitoring nests on the ground in KNP, we are continuing to follow our tracked eagles to determine the frequency and causes of mortality, as well as the breeding status of our tracked birds to gain a more comprehensive understanding of the environmental drivers of breeding performance.

Additionally, we have collaborated with the Endangered Wildlife Trust (EWT) on their project monitoring the Martial Eagles nesting on power pylons in the Karoo. This population may be the largest in South Africa, yet little is known about their productivity rates or survival, and whether this population may be acting as a source population for the rest of the region. .

Activities in 2022

  • Kyle Walker completed his analyses and will submit his MSc thesis in Feb 2024. Kyle’s research explores how this species may respond as temperatures warm due to climate change. He investigated how provisioning rates of adults to their nestling change in hotter conditions, and whether diet flexibility may allow this species to adapt to rising temperatures. This analysis uses data from 12 camera traps that were placed at nests during the nestling period.
  • We re-analysed the breeding data collected from 2013-2021, alongside the GPS tracking data. These analyses have shown that GPS tracking can improve the accuracy of breeding estimates. We also reviewed the financial and carbon costs of traditional field monitoring, versus GPS tracking projects, and found that the latter method is considerably more cost-effective.
  • This new analysis based on GPS tracking suggests that the productivity of this population is higher than previously estimated through field monitoring alone. Using these revised productivity estimates, within the population models built by Rowen van Eeden, it appears that the Kruger population may actually be self-sustaining.
  • Jane Doherty completed her Conservation Biology mini-thesis exploring the breeding success and survival rates of Martial Eagles breeding in the Karoo. This thesis uses EWT monitoring data collected over the last three years. Jane fed breeding and survival estimates into a Population Viability Analysis to explore the sustainability of this population. Unfortunately, this population does not appear to be as sustainable as first thought, with relatively high mortality rates suggesting that this population is unlikely to be functioning as a source population .

Highlights

  • Megan Murgatroyd, Arjun Amar and Gareth Tate published a paper in Royal Society Open Science showing the benefits of monitoring breeding productivity of Martial Eagles using tracking devices.
  • Jane Doherty graduated in December 2023 with a MSc Conservation Biology. Jane presented her research findings at the EWT conference in Swadini, near Hoedspruit in November.
  • Arjun Amar was a co-author on a paper, published in Nature Ecology and Evolution, which explored changes in raptors across African Savannas, this included the Martial Eagle which had declined by over 90% over 3 generations lengths. These findings suggest that the IUCN status of this species may need to be reconsidered for uplisting. 

Impact of the project
Our research provides a better foundation for protecting this Endangered species, within the most important areas for this species in South Africa.

Key co-supporters
AABAX Foundation; Anthony Sedgewick, DSI-NRF CoE grant; Endangered Wildlife Trust (EWT); Jock’s Safari Lodge; SANParks; Eskom.

Research team 2023
A/Prof. Arjun Amar (FIAO, UCT)
Dr Megan Murgatroyd (HawkWatch International / EWT / FIAO, UCT) 
Dr Gareth Tate (EWT) 

Students: Kyle Walker (MSc, UCT), Jane Doherty (CB MSc, UCT).