Martial eagle sightings have dropped by as much as 60% since the late 1980s, in stark contrast to human population growth across their shared natural habitat, the study published this week in the scientific journal Bird Conservation International found.
Although the exact reasons for the decline remains unclear, researchers say their findings point to an urgent need to better understand the threats to the bird.
The study also highlighted a decline in Martial eagle sightings within protected areas, including the Kruger National Park and the Kalahari Gemsbok National Park.
However, declining numbers of the species in protected areas were not as severe as elsewhere, suggesting that these areas could act to limit the factors leading to the sharp decline.
Dr Arjun Amar and PhD student Danië* Cloete from UCT’s FitzPatrick Institute of African Ornithology conducted the study using two Southern African Bird Atlas Project surveys carried out 20 years apart.
Their previous research showed that comparing these surveys provided an accurate way of measuring changes in the population size of this species.
Martial eagle total population figures are still relatively inexact, but their conservation status was uplisted in 2013 from Near Threatened to Vulnerable - which means they are recognised to be globally threatened.
Martial eagles mainly prey on large birds and reptiles, and small and medium-sized mammals, but are strong enough to prey on small antelopes. They typically nest in high treetops.
The study found significant declines in KwaZulu-Natal, Mpumalanga and Limpopo.
Changes differed across the biomes, with the species faring worst in the Grassland, Savannah, Indian Ocean Coastal Belt and the Nama Karoo biomes.
In the Fynbos biome of the Western and Eastern Cape, reporting rates remained more stable over the last 20 years.
“Despite having full legal protection in South Africa, this species is known to be targeted and killed by farmers who blame the species for predation of their livestock, or may be accidentally killed by poison left to kill other predator species,” the authors noted.
Another major threat for Martial eagles is infrastructure, including power lines, particularly among juveniles.
Amar said quantifying the decline of the species in the country was the first step in saving the bird.
“We now need urgent research to better understand the factors that are responsible for causing this iconic species to be lost from our countryside, so that these factors can be better controlled,” Amar said.