When night falls in Beijing, and the world retreats into silence, Terry Townshend knows the predawn darkness is a migrant highway — an invisible river of wings, calls, and journeys spanning hemispheres every spring and autumn.

"As we're sleeping in our beds at night, there's this invisible miracle happening over our heads," he says. "Billions of birds move across continents. And most people never even know."

About 16 years ago, Townshend, a British environmentalist, never imagined this would be his life. Then working for a London-based nongovernmental organization, he arrived in Beijing in 2009 to assist drafting the environmental laws. When funding for his organization dried up two years later, he found himself jobless and "stuck in China", as he puts it. Rather than retreat, he leaned into a childhood passion: birds.