Scientific Services

Martial eagles are declining both inside and outside protected areas. However, the drivers behind these declines are unclear. In Kruger National Park, recent research provided invaluable insights into the diet and feeding behaviour of breeding martial eagles

Martial Eagles, savanna biome specialists, are listed as Endangered on the IUCN’s Red List. Camera trap footage collected at nest sites inside the Kruger National Park have been used to assess the diet of eagles during the breeding season and to model the influence of climatic conditions on prey provisioning.

The martial eagle (Polemaetus bellicosus) is the largest eagle in Africa, occurring in savannas and woodlands. Lower reporting rates of these birds between two subsequent South African Bird Atlas projects in 1987-1992 and 2007-2012 suggest that the population has experienced large declines both inside and outside of protected areas. This has led to martial eagles being listed as ‘Endangered’ on the IUCN’s red list.

Martial eagles rely heavily on protected areas, and it is particularly worrying that in South Africa, large declines in reporting rates have also been found within a historical stronghold – Kruger National Park. Kruger currently only has approximately 100 pairs. In an attempt to better understand the species behaviour and ecology, researchers from the University of Cape Town and HawkWatch International are investigating the diet and feeding behaviour of martial eagles, looking specifically at how higher temperatures, a concern under climate change projections, may influence the rate of food delivery and the type of prey delivered to a nest, and ultimately breeding success.

Male eagles feed a larger proportion of birds/mammals to martial eagle chicks, with reptiles making up only 16%. On the other hand, 91% of the diet fed by female birds are reptiles and mammals, with only 8% of the diet comprising birds. There seems to be clear sex-based differences in prey selection.

During 2018-2022, camera traps placed on martial eagle nests throughout the park captured 28,000 images. A total of 44 different prey items were fed to chicks during the breeding season with monitor lizards and helmeted guineafowl (Numida meleagris) forming the dominant prey. Most notably, adult males feed considerably more birds to chicks (54%) than adult females (8%), and it is primarily the male’s responsibility to feed the chick throughout the early stages of development. During the later stages of chick development, feeding responsibility shifts to the females because the chick is older and can be left unattended for longer periods of time. During this time, females predominantly feed monitor lizards to the chicks. Monitor lizards weigh almost twice that of guineafowl, reflecting the species’ sexual dimorphism (i.e. males are smaller than female martial eagles). At higher temperatures, martial eagles feed more monitor lizards than birds to their chicks.

As reptiles are more active than birds at higher temperatures, this came as no surprise. It also suggests that martial eagles may be buffered against the impact of a changing climate by hunting prey that are more abundant during high temperatures, which could be advantageous with hotter and drier temperatures.

Martial eagles, vultures, southern ground hornbills, secretary birds, Pel’s fishing owls and other eagle species are listed under Kruger’s Species of Special Concern Programme. A ranking procedure enables prioritisation of species within Kruger so that monitoring, and management effort can be allocated accordingly. This study has provided a more comprehensive understanding of diet and feeding behaviour of this important species of special concern. The specific drivers of decline in this population have yet to be firmly established but habitat loss and low adult survival due to persecution or electrocution during wide-ranging movements outside protected areas, remain a possibility.

The deployment of cameras has also revealed fascinating interactions between martial eagles and other species. For example, nest predation by leopard was captured on two separate occasions in 2022, as well as an incident of predation by a honey badger in 2018.

This article was written by Kyle Walker, Arjun Amar, Megan Murgatroyd and Sharon Thompson and originally published in the 2022/2023 Research Report.