Finding affordable housing in China is tough. There's not enough units in our market. The reserve now provides some one-bedroom apartments for us. There's no room for a microwave and the bathroom is shared. But the rent is free.

The mergansers have high standards for habitat. Their water must be sparkling clean, and they need hollow trees, or something else that does the job.

Over many decades, as humans have left their mark on the planet, suitable nesting places have been reduced.

Unfortunately, the great forests of Changbaishan Mountain have dwindled since the 1970s, and along with them so has the the population of the Chinese merganser.

The species was listed as threatened in 1988, vulnerable in 1994 and endangered from 2002 to 2017, according to a red list prepared by the conservation union.

Critically endangered may come next, but the experts hope to avoid that.

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The nature reserve is putting nesting boxes in trees, removing fishing nets from rivers and requiring that newly hatched fish be released to maintain the ducks' food supply, according to Cui Zhigang, deputy head of the reserve's wildlife protection bureau.

Last year, the government of Jilin province launched a program to bring the population of Chinese mergansers in Changbaishan up to at least 600 during prime reproduction season by 2025, and to 800 by 2030, Cui said.

In the nesting box project, workers attach wooden dwellings to trees 10 to 20 meters off the ground. Some elaborate boxes are disguised as hollow tree trunks to fool adult females into adopting them as home and laying their eggs inside — typically one per day for seven to 13 days.

After a month of incubation, a family of fluffy chicks emerges.

When they're old enough, the mother demonstrates how to leap from the tree. They follow her example, one by one, springing into the air and trying to fly but mainly just falling like fuzzy tennis balls onto a practice court.

In November, after the chicks have grown, most Chinese merganser families wing it south for the winter, returning to Changbaishan Mountain in April. The arduous migratory cycle can stretch over thousands of kilometers.

The round trip includes domestic sights and a few foreign ones. A smattering of the birds have been seen in China's Jiangsu, Jiangxi, Hunan and Taiwan, as well as in Russia, the Democratic People's Republic of Korea and Japan, Piao said.

Their migratory cycle has repeated itself since before the time humans started walking upright.

Chinese mergansers don't need the high-tech navigation gadgets or flight controls of a jetliner. They complete their journeys flawlessly on instinct alone.

On trips to and from Jilin, they like to lay over in coastal cities in Shandong province; Qinhuangdao, Hebei province; Dandong, Liaoning province; and elsewhere. Experts have been cataloging the routes.

For Piao, however, the mergansers are more than a science project. "After three decades of companionship, they are like my children," he said.