Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

CHEORWON, South Korea — Moments before dawn, in a still black sky, a trembling roar is heard near the Demilitarized Zone separating North and South Korea.

The sound is not the latest volley in a 65-year-old conflict. Instead, it is from thousands of migratory birds taking flight, rising in unison from the frozen surface of a reservoir. Among them are hundreds of endangered red-crowned cranes, which scientists are now working hard to save.

“Cranes bring peace, long life,” said Dr. Chun Jae Kyong, CEO of South Korea’s National Nature Trust. “Korean people believe they give them happiness.”

Yet peace is the very thing that could threaten these majestic birds, among the largest and heaviest of all crane species. Since its creation 65 years ago, the DMZ has become an accidental nature preserve home to some 5,000 species, more than 100 of which are considered protected by the South Korean Ministry of Environment.

As the sun rises on one frozen morning, South Korean guard posts stand nearby. A look through binoculars reveals North Korean guards two and a half miles away. The space between the countries stretches 160 miles, creating a vast, largely untouched no man’s land where nature has been allowed to flourish. Now as the two Koreas are exploring ways to reconnect, the long-awaited diplomacy is potentially putting the unspoiled ecology between them in peril.

An abandoned guard post near the DMZ. Kyle Eppler / NBC News

Just south of the DMZ sits Cheorwon. Once bustling, today it is a small farming town. Residents here have embraced the annual arrival of the endangered red-crowned crane and the vulnerable white-naped crane before the birds return north to China and Russia. The best estimates suggest about 850 red-crowned cranes — or 30 percent of their worldwide population — visit each winter.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Local hospitality has helped attract the birds. Their winter habitat used to sit squarely inside North Korea, but famine there in the 1990s forced them south. Here, fallow paddy fields provide nourishment along with rice and corn spread twice each week by environmental preservation groups.

Slowly, biologists have seen their numbers in the region increase — but they have reason to fear a setback.

Today, railway tracks that would connect North and South Korea end abruptly at the edge of the the DMZ and a locomotive sits idle. Last year, however, the United Nations approved a joint study by the two countries to examine re-linking the line, making development a real possibility in a region previously considered too risky to invest.

“If the railway was built up, this area will be the center of commerce,” Chun said. “So it will encroach the habitat of the cranes.”

There’s already one big investor — the South Korean government.

A white naped cane in a field. Kyle Eppler / NBC News

In February, South Korea announced an $11.75 billion-dollar plan to revitalize the country’s inter-border regions. Some of the money will be set aside for eco-tourism projects, but plans also call for a unification and cultural exchange center to be built in Cheorwon. Hotels and shopping malls would likely follow. Should a “reunification city” be constructed as some have proposed, and the fortified border soften, the building could eventually encroach into the pristine land of the DMZ itself.

“Obviously, we have to achieve reunification and need to have development,” said Baek Jong Han, chairman of the Crane Association of Cheorwon. “As long as the government can help create some kind of environment where these cranes can be protected.”

For its part, South Korea’s Ministry of Unification said it will “protect the habitat for the cranes as much as possible.”

“This is really the big picture of the design for the new economy that we will pursue — not only development, but preservation of the environment,” ministry spokesperson Baik Tae Hyun told NBC News.

The International Crane Foundation, headquartered in Wisconsin, said serious reunification talks must include a focus on the ecology of the area.

“The key to it all is getting conservation on the agenda,” said Spike Millington, vice president of international programs for the ICF. “People always want to improve on nature, but what would have the longest-lasting impact is ‘Wow, this is a pristine ecosystem, it’s the only place in the whole world you can see this,’ so I think we have a chance.”

Chun’s National Nature Trust hope the cranes symbolism can serve as that olive branch.

“Cranes could connect North Korea people and South Korea people in history and culture,” he said.

He’s not alone. In Cheorwon depictions of cranes adorn buildings, bridges, and signs, but for Baek they are much more than a mascot: “If these cranes no longer come to Cheorwon because of environmental damage, then Cheorwon will be losing its children.”