Africa’s Largest Eagle Needs Its Space—and Lots of It
Published by the Natural Resources Defense Fund
Chris Eason/Flickr
The martial eagle of sub-Saharan Africa can make some pretty impressive dives. With wingspans approaching nine feet, these gray-and-white raptors can take down a goat. Unfortunately, the eagle’s population is taking a steep plunge, too.
The species numbered in the tens of thousands as recently as 2001, but its conservation status has been falling fast since then. The International Union for Conservation of Nature declared the raptor vulnerable to extinction in 2013, up from a near threatened status given to the species in 2009. The Southern African Bird Atlas Project, which covers eight countries, suggests a decrease of more than 40 percent in that region alone.
Martial eagles often get electrocuted by power lines, hit by cars, and are sometimes even chopped into pieces for sale in traditional medicine markets. Also, farmers take issue with the bird’s habit of attacking small livestock. While these apex predators typically prefer hares, striped polecats, genets, mongooses, and ground squirrels, they won’t turn their beaks up at an occasional lamb. Some farmers shoot the birds on sight or lure them into baited traps. Larger, commercial farming operations choose to snuff out the eagles with poison-laced meat.
So, most of the martial eagle’s problems result from run-ins with humanity. In fact, you’re five times more likely to see a martial eagle in a protected area than a non-protected area. National parks and refuges have traditionally been strongholds for these species, but recently scientists have begun to worry that even these sanctuaries won’t be enough to sustain the species. Since 1987, Kruger National Park in South Africa, for instance, has showed a higher decline in martial eagle populations (54 percent) than the country as a whole.
Which begs a troubling question: If martial eagles can’t survive in one of the largest national parks in the world, what hope do the birds have across the rest of the African continent?
Rowen van Eeden, a conservation biologist at the University of Cape Town’s Percy FitzPatrick Institute of African Ornithology, says martial eagles are particularly difficult to conserve because they are sensitive to human disturbance, reach sexual maturity at five to six years old (late for a bird), and when they do reproduce, they only fledge a single eaglet every two to three years. Making matters worse, according to a recent study conducted by van Eeden, martial eagles require enormous territories—of about 40 square miles each.
That means one adult needs an area almost twice as big as Manhattan to survive.
The researchers fitted eight martial eagles within Kruger National Park with ultralight GPS backpacks and then monitored their daily flights for up to three years. Half of the eagles stayed put within their Kruger territories. (Those were the lucky ones.) Interestingly, two other eagles never showed signs of holding a territory and instead lived a mostly nomadic lifestyle. These birds covered an extraordinary distance of 17,000 square miles throughout their monitoring. Another two abandoned their Kruger territories. What led these eagles to fly the coop is unclear, but van Eeden and his team suspect the reasons are environmental degradation or lack of prey or both.
In any event, it would appear that this shift in behavior comes at a heavy cost. Of the four wandering eagles, three died as a result of nonnatural causes.
One bird soared south to Swaziland, where it was electrocuted. Two others met their ends at the hands of hunters in Mozambique to the east, one of them suffering in a snare. The final bird, a female who had failed several times to fledge any young in 1,087 days of tracking, disappeared into Zimbabwe. Her fate is unknown.
The researchers, of course, are interested in more than the individual lives and deaths of a handful of birds in South Africa. The study marks the first time anyone has ever quantified adult martial eagle ranges, which means not only do we now know how much area the birds need for hunting (quantity) but also what kinds of habitat they seem to prefer (quality).
According to the study, the birds tended to select areas with higher percentages of tree cover and dense bush. The eagles also seemed to avoid more open areas such as low-lying grasslands.
This may seem like a trivial finding, but it could be crucial to the raptor’s conservation. Protecting the entirety of their range is not always possible for species that roam over such huge tracts of land. A population of 100 martial eagles, for instance, would require a human-free sanctuary the size of a small country such as the Gambia. The next best option would be to work to alleviate the dangers people pose in the areas we share with the birds. But even this strategy would fall short if the eagles can’t find suitable habitat. That’s why we need to prioritize providing the dense bush and tree cover martial eagles fancy.
Unfortunately, Kruger National Park has lost a lot of its tree cover in the last half century as a result of prescribed burning (which was once thought to prevent larger, more damaging fires). Rises in elephant numbers within the park have also contributed to less tree cover, as the giants like to pull down whole trees to get at their leaves. Perhaps it’s no surprise then that in places where elephants are prominent, martial eagles tend to disappear.
In areas without tall nesting trees, van Eeden says these birds usually make their homes in large power pylons or other artificial structures. Whether this makes them more likely to die from unnatural causes, such as electrocution, no one knows. What we do know is humans could stand to help them out in the habitat department and poisoning department. Perhaps then we could see numbers for these majestic birds soar again.
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