"Large animals are usually less sensitive to the flying vehicles. But we had to figure out how to avoid scaring small animals like monkeys," Yu says.
"The monkeys would hide if they heard our drones, even if they were a kilometer away."
The crew used such tactics as dangling bananas from drones and fastening cameras to helium balloons. But they lost two cameras when the balloons to which they were connected flew away.
Yu says he remains hopeful someone will find and return the cameras so he can edit the clips into an adventure tale featuring the balloons as the protagonists.
While it's impossible to avoid all mishaps, veteran drone pilots, and especially those who've filmed wildlife for years, can reduce accidents.
For example, an experienced drone operator would fly a certain distance from migrating birds to make them feel more comfortable about their unique "companion". The drone would then slowly move in closer, as the flocks feel more relaxed.
The most breathtaking scenes required patience, persistence and a bit of luck, Yu says.
He recalls that filming the misty Dongjiang Lake in Central China's Hunan province was one of his most impressive expeditions.
