Disturbing decline in Kruger’s Martial Eagles investigated
Rowen van Eeden
Percy FitzPatrick Institute, UCT
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With an ever-increasing human population, our natural heritage is under ever greater pressure as natural habitats are degraded to meet growing energy and food demands. National parks provide pivotal refuge for species that are unable to cope within these highly transformed habitats. Birds of prey, such as Martial Eagles, are an example. Africa’s largest iconic eagles, they rely heavily on protected areas for their survival.
A dramatic decline in South Africa’s Martial Eagle population has been highlighted in comparisons between the first Southern African Bird Atlas Project (SABAP1) that took place from 1987 to 1991 and the second, SABAP2, from 2007 to 2012. A similar trend emerged after comparison of historic and contemporary population data. It is evident that populations have declined by 60%, with a concomitant range reduction of 53% over the last 20 years. As a consequence, the species has recently been uplisted to Vulnerable by the International Unions for Conservation of Nature (IUCN).
Declines of Martial Eagles in South Africa’s protected areas have also recently been recorded, and of particular concern is a decline within the Kruger National Park (KNP). It has become paramount therefore that the causes of such population declines be identified and appropriate conservation actions be implemented.
As a result, researchers from the Percy FitzPatrick Institute, in partnership with SANParks and the Endangered Wildlife Trust, are investigating the ecology of Martial Eagles in KNP. Since 2013, they have been assessing the birds’ breeding success, and the juvenile and adult survival, using cutting edge GPS tracking technology. These devices are enabling them to understand how the eagles use their habitat in the park. It will also allow them to accurately identify causes of mortalities by tracking the last known locations of individual birds.
To date, the project has highlighted some interesting new findings previously poorly understood by biologists. At the same time, results have confirmed aspects of their ecology formerly determined by using traditional research techniques. For instance, previous Martial Eagle territory size estimates determined using colour rings or wing tags were thought to be enormous, ranging from 125 to 300km2. This has been confirmed by GPS tracking which has allowed the team to accurately determine the eagles’ territory size and to assess just how territorial they are.
In the Kruger, territory sizes average 114km2 and birds seldom cross into their neighbour’s territory. This means that this park could potentially host up to 170 pairs. Findings have, however, also indicated that not all adult birds hold territories, with some individuals covering extensive distances. One female wondered as far as Inhambane on the Mozambique coastal plain, before returning to the park. Some recently fledged birds have also shown extensive dispersal from their nesting areas, traveling hundreds of kilometers from the boundaries of the park.
One hypothesis for the species’ decline is that these roaming adults and dispersing juveniles are regularly under threat from collision with power lines or persecution from farmers who fear livestock losses to these iconic raptors. As juvenile birds succumb to unnatural mortalities, there are fewer individuals to recruit back into the KNP to replenish an aging adult population. Luckily, as of yet no mortalities have been detected through the GPS tagging programme, which is currently monitoring the movements of 12 individuals.
To supplement the GPS tagging programme, adult Martial Eagles are colour ringed to monitor their survival over time. This is only possible if a massive effort is made to re-sight the ringed birds on a regular basis. Visitors to the park can make a valuable contribution by reporting re-sightings of colour- ringed Martial Eagles in the books at reception areas. Alternatively, e-mail the location, date, time, ring colours and, if possible, a photograph of the bird to [email protected].