The world’s largest predators are also some of the most endangered. From tigers in India to lions in Africa, humans have hunted them down and encroached on their habitat. Recently, another major threat has emerged in Africa: animals at the top of the food chain are running out of prey.

Herds of impala, wildebeest, kudu and other large herbivores are in decline across sub-Saharan Africa, in part due to rising levels of poaching by hunters seeking bushmeat for subsistence and profit. A recent studyfound that poachers in Botswana’s Okavango Delta were killing the equivalent of more than 15,000 impala every year.

In Zambia, scientists have now documented both the toll this is taking on predators and found promising evidence it can be addressed at least in part by cracking down on poaching.

“Even in a huge, unfenced ecosystem that’s already heavily affected by humans, we can reverse the decline by increasing the investment in protection—we just need the will to do it,” said Scott Creel, a Montana State University ecologist who has spent years studying predators in this part of the world.

Creel’s work tracking African wild dogs shows, in detail, the way a shortage of prey can deplete a highly endangered predator. For years, it was thought that one of the biggest threats to these large-eared dogs was their larger rivals, such as lions and hyenas. Hyenas, which are twice the size of the dogs, will steal a carcass from them. Lions will kill the dogs outright.

In the late 90s, Creel wrote a paper stating that “wild dogs are rarely limited by prey availability.” But with the passage of nearly 3 decades, developments in these ecosystems coupled with new research has the Montana scientist changing his tune.

To see how a shortage of prey affected wild dogs, Creel’s team fitted GPS tracking collars on animals in more than a dozen packs in two large Zambian ecosystems. Between 2013 and 2021 they observed their movements both with the satellite collars and by following them in person, watching how far the animals traveled and when they walked, ran, or broke into all-out sprints to chase down prey.

The research revealed that in areas with less prey, the dogs traveled further and shifted their focus to smaller, less energy-rich prey, the scientists reported last week in the Proceedings of the National Academy of Sciences. That means the animals were at greater risk of an energy deficit—not a recipe for success.

“Wild dogs were always limited from the top down by their competitors,” said Creel. “That they switched from being limited by their competitors to being limited by food is a new thing, and unfortunately, very worrisome.”

While lions in these same ecosystems aren’t threatened by attacks from other predators—except humans—the loss of prey has affected them as well. Recent research concluded that the two biggest threats to lions are killings to retaliate for livestock depredation, and the loss of prey. In Zambia, Creel and colleagues have traced prey depletion to lower numbers of leopards, wild dogs, and lions.

In 2018, the scientists got a chance to test whether a crackdown on poaching would help. After years of limited policing due to lack of money, that year the Zambia Department of National Parks and Wildlife was able to increase anti-poaching patrols in some areas, thanks to an infusion of funding from conservation groups.The researchers had already been tracking the lion populations in 8,000 square kilometers of woodland and grassland in and around western Zambia’s Kafue National Park. The sudden boost in poaching enforcement offered a way to see how much of an effect it had on lions.

It was an open question whether such patrols could make a difference if it wasn’t accompanied by fencing off protected areas, according to Creel.

But even without these barriers, the scientists quickly saw signs that the lion population was rebounding in heavily patrolled spots. Over four years, from 2018 through 2021. The change was most evident in the number of cubs, which increased substantially in places with high protection levels. Lion prides in those places had 29% more new cubs than in places with less protection, the researchers reported at the end of December in Conservation Science and Practice.

While part of the benefit could have come from fewer lions getting caught in poachers’ snares, the biggest effect was because there was more prey for lions to eat, said Creel. Overall, lion populations in those same patrolled areas grew fast enough that lion numbers could double in a decade, while they continued to decline elsewhere.

“That’s a good news story in the face of these problems,” said Creel. “It definitely shows that even in a big ecosystem that potentially can hold a huge population, increased investment works,” he said.

Creel, et. al. “Prey depletion, interspecific competition, and the energetics of hunting in endangered African wild dogs, Lycaon pictus.” Proceedings of the National Academy of Sciences. Jan. 27, 2025.

Creel, et. al. “Changes in African lion demography and population growth with increased protection in a large, prey-depleted ecosystem.” Conservation Science and Practice. Dec. 24, 2024.