Early one morning in the CCZ, Choi takes me to a river where cranes gathered for the night. Several dozen are still there. Choi says cranes prefer to roost in running water. We huddle behind a barbed-wire fence. Although it’s too dark to see the birds well, we can hear them nattering among themselves. Then we hear a series of louder calls. “Unison call,” Choi says.
The unison call is an elaborate duet by a mated pair of cranes. It is thought to strengthen the pair bond, claim territory and intimidate competitors. Each species of crane has a unique unison call. For a pair of red-crowned cranes, the male initiates the call, throwing his head back and letting out a loud rising whoop. The female answers with two notes descending. Standing next to each other, the pair will repeat the call several times.
We watch as other cranes glide in to join those already in the river. They fly awkwardly, their long legs bent and tucked under their feathers. They have come from the opposite hillside, where a line of large, widely spaced orange squares stretches as far as I can see. Choi says the patches are a warning for South Korean pilots, marking a boundary they are not to fly over; if they do, they risk crossing the border and getting shot at by the North Koreans.
I ask Choi if he ever worries about his safety, working as he does so close to the border. He shrugs. The cranes are not scared, he says, so he is not scared. We fall silent and listen to the cranes in the silver river, silhouettes against shadowed mountains in the cold dawn crying out to each other.
Eric Wagner wrote a series of dispatches from a penguin colony in Argentina for Smithsonian.com. He lives in Seattle.