The sound was like nothing Tom Hinton had ever heard before: a chorus of baleful wolf howls, long and loud and coming from seemingly every direction in the darkness. The predators yipped and chirped and crooned to one another for what seemed like forever, sending a shiver of awe and intuitive fear down Hinton's spine.
"It was a primordial experience," he said, something most of humanity hasn't felt for tens of thousands of years. "That dates back to when humans were prey."
It was only possible because of where Hinton was standing, a remote area along the Belarus-Ukraine border that's been uninhabited by humans for decades.
They all left in the wake of a very different sound nearly 30 years earlier: the massive explosion of the Chernobyl Nuclear Power Plant in 1986, which left dozens dead and drove more than 100,000 people from their homes across a 2,574-square-kilometre swath of Ukraine and Belarus. These days, abandoned apartment complexes are nothing more than crumbled concrete wrecks. Vines crawl up the decaying walls of old farmhouses and break unintended skylights into their roofs. No one lives in the post-apocalyptic setting.
No one human, that is. Wildlife populations there - shaggy-haired wild boar, long-legged elk, the howling choruses of wolves that so captivated Hinton last August - are flourishing.
That's according to a study published this week in the journal Current Biology, which found that mammal numbers in the exclusion zone are as high, if not higher, than in even the most protected parks in Belarus.
"That wildlife started increasing when humans abandoned the area in 1986 is not earth-shattering news," Hinton, a radioecology expert and co-author on the paper, told The Washington Post. "What's surprising here was the life was able to increase even in an area that is among the most radioactively contaminated in the world."
In other words, whatever the fallout from the disaster may have been, it turned out that the absence of humans was more than enough to compensate.
"It shows I think that how much damage we do," said fellow co-author Jim Smith, an environmental science professor at the University of Portsmouth. "It's kind of obvious but our everyday activities associated with being in a place are what damages the environment."
"Not that radiation isn't bad," he added, "but what people do when they're there is so much worse."
The study is the first real census of wild animals in the exclusion zone. It relies on a decades worth of helicopter observations in the years right after the disaster, and three winters of scientists carefully counting animal tracks on foot between 2008 and 2010 in the Belarusian section of the zone.
Though animal numbers were low when scientists first started counting them in 1987 (because no data was taken before the disaster, they can't tell to what degree the populations were hurt by the explosion), they rapidly rose once humans left the region. Brown bears and rare European lynx - predatory cats the size of a Great Dane with tufted ears and glimmering gold eyes - quickly appeared in the forests, even though they hadn't been seen for decades before the accident. Wild boar took up residence in abandoned buildings. Forests replaced humans in the villages' empty streets.
Within 10 years, every animal population in the exclusion zone had at least doubled. At the same time, the kinds of species that were flourishing in the exclusion zone were vanishing from other parts of the former Soviet Union, likely due to increased hunting, poorer wildlife management and other economic changes.
By 2010, the last year of the on-foot census, the populations for most species were as large as in any of Belarus' four national parks. For one species, the wolves, the population was seven times bigger.
This indicates to researchers that chronic exposure to radiation from the explosion has had no impact on overall mammal populations. Whatever fallout may have come from the initial explosion was completely offset by the benefits of life without humans.
This doesn't mean that the zone isn't dangerous, Hinton stressed. He and his colleagues didn't study the individual- and molecular-level damage caused by lingering contamination. While whole populations aren't dying out, individual animals might be getting sick. And surveys have shown that the soil in areas close to the reactor site still exude radiation.
But, "the environment is very resilient," Hinton said.
The presence of wolves is particularly telling. As apex predators, they are a sign of the health of the entire ecosystem - if they're flourishing, that means that every other level of species, from elk and deer on down to insects and plants, must also be healthy.
Another team of researchers is currently using camera traps to count wildlife on the Ukrainian side of the exclusion zone. Nick Beresford, a radioecologist at the National Environment Research Council in the U.K., said that their work won't be done until the end of the year, but he expects to reach the same conclusions as those working in Belarus.
Beresford praised the Current Biology study and its findings: "People have said before that wildlife in the zone is flourishing, but those accounts were rightly criticised as anecdotal," he said. "This is the first study to really back it up with science."
Walking around the exclusion zone is like being in "a national park without the people," Hinton said. The forests are nearly pristine, the animals abundant. What relics of human presence do remain have been almost entirely reclaimed by nature.
Even the Soviet city of Pripyat in Ukraine, which once housed tens of thousands of workers at the Chernobyl plant, has been subsumed by trees.
"When I was there 15 years ago, it looked like a city with some trees growing in it," recalled Smith. "Now it looks like a forest with some buildings in it."
For Hinton, who is currently studying the effects of the 2011 Fukushima nuclear disaster in Japan, the impact is both astounding and sobering.
"It's an amazing experience from a wildlife perspective, but it's also a sad experience because you see homes that have been abandoned and you imagine the people's lives that have been disturbed," he said. "It's sad to see the houses and the cars and the baseball bats and you envision the life that people had to drop and leave. But you also see wild boar running around and you don't see that as soon as you leave the zone."