Subtitles section Play video Print subtitles More often than not humans have a negative impact on the natural world. But once in a while, an opportunity comes along to bring an ecosystem destroyed by us back from the brink. A national park in Mozambique is giving scientists, this very change by providing a unique opportunity to restore an ecosystem and demonstrate the surprising role predators play in maintaining balance. They're hoping to capitalize on a unique ecological effect observed in the natural world... Fear. This is Gorongosa National Park. It's quickly becoming one of Africa's, and perhaps the world's, greatest wildlife restoration stories. We had really high densities of animals like buffalo, elephant and a host of other ungulate species so it's very rich in its biodiversity and specifically in its large mammal populations. Lions, leopards, hyena, were all here. But the war pretty much wiped that out. From 1977 to 1992 a civil war devastated Mozambique and killed more than 90% of the large mammal populations in Gorongosa. Though so many of the animals were gone, many hunted with little protection during the war, the land and vegetation was still largely intact. So once rangers secured the park from poaching many herbivore populations began to rebound. Others got a little bit of help from the scientists. The elephant population is increasing. Species like waterbuck, impala, reed-buck, warthog are just on the up. So, this system is really ready for this type of recovery. In comparison large carnivores didn't make such a strong recovery initially. And while the waterbuck and the impala probably didn't mind. Over time, a lack of large predators can tip the balance of the ecosystem, we start to see these signs of imbalances and these missing pieces, very clearly in Gorongosa. In the absence of fear, in the absence of predation, certain species just skyrocket. The other thing we see are animals that are behaving a little differently to what we would consider normal. Without predators to keep the prey alert and in line, the herbivores can go wherever they please in search of a good meal. Bush-buck is normally a pretty reclusive species. They're not a species that normally drifts out into the open. But in the absence of predation we've actually seen bush-buck take those chances. We'll see them out on open floodplain foraging on some pretty nutrient rich plants. So in the absence of predation they're willing to take that risk and venture out into areas that they usually seek refuge in. Sounds ideal for the bush-buck. But it's a warning sign of an ecosystem out of whack. If animals don't stay in their lanes the whole system can spiral out of control. This is where the predators come in. Sure they eat some of the prey. But importantly they instill what scientists call a landscape of fear, just the presence of predators changes the prey's behavior, forcing them to be more vigilant and take fewer risks. Lions are one predator that was slowly recovering in the park. And while they did their part in going after some prey animals. They weren't doing enough. A lion is an ambush predator. They hang out in tall grass on the edge of the floodplain. And they take down their prey using stealth. The ambush-hunting lions were certainly being noticed by the prey species they went after, but their tactics and territories were not enough to impact the whole park. The team realized that other predators, with different hunting styles were needed - top of their list was the painted wolf - a wide roaming pack predator, that had been well established in Gorongosa before the war. So there's nothing like a painted wolf on this continent, they're unique, they have this gorgeous camouflage coat pattern and every individual is differently colored and differently patterned, their teeth, their paws have evolved to support them being one of the continents most exceptional hunters. The African painted wolf is considered one of the most successful predators on the planet, but how the animals hunt, specifically that they go after their prey using a different hunting method than lions, was really why the painted wolf was chosen. A painted wolf pack. They're not stealthy in the least. They chase down their prey and sometimes they'll go miles chasing down an animal. So, very different ways of hunting, that actually complement each other in the ecosystem. Bringing the predators back to Gorongosa was also an unprecedented opportunity to help save the species. There are only roughly 7000 painted wolves left on the planet, but reintroducing a species, especially a predator is a massive undertaking. The range of action includes many steps. When they arrive in Gorongosa, they're kept in a temporary enclosure, where they're safe. Once the pack arrives and they're in the enclosure, we begin the process of habituation. Most of those members in the pack that we want to bond have never met each other before directly. And we use a novel scent-marking procedure where we actually rub dogs while they're still sleeping against each other to leave the scent on each other, so that when they woke up, there wouldn't be so much aggression. Paola and her colleagues kept the painted wolves in an enclosure, so that they would form a well functioning pack before taking off on their own. This careful scientific approach to conservation allowed Paola and her team to release the new predators into the larger Gorongosa wildlife population, knowing there is a good chance they could help rebalance the ecosystem and unleash the power of fear. Right off the bat, it was really clear that the painted wolf reintroduction was succeeding. The packs were hunting successfully. We had different packs form on the landscape, we had pups born. And in addition to thriving themselves, the painted wolves settled nicely into their role as a regulating predator. This is a long term, effort, but even in these initial stages we're starting to see the signs of a system coming back into balance. Bush-buck that would be normally out in the open taking chances because there were no predators there before are now more reclusive. And so, in a sense, you start to see species falling back into their more predictive ecological lanes. It's still too early to tell how Gorongosa will be affected as the painted wolves establish new generations. It helps that the scientists collected so much data throughout their sustained conservation efforts. So, they'll be able to track any changes and developments in the ecosystem as they happen, but there's already proof of success. 52 new pups were born in 2020. 37have survived the denning stage, a survival rate of 71%, which is incredible, compared to the average rate of less than 50%. This brings the total Gorongosa painted wolf population to 85 dogs and five packs. These are still the places where the complex ecology that supports a habitable planet, still exists. And so no matter where you go on this planet right now. These systems need healers and defenders and so that's what drives us here, that's what gets us up early and works late into the night is that opportunity to make a positive difference. For more on Gorongosa's landscape of fear and the return of the wild dogs, check out nature's Fear Factor streaming now on pbs.org.