In the summer of 2021, he thrice spotted snakes approaching in the surveillance footage and each time without hesitation, he rushed to drive them away, erecting an invisible barrier for the birds.

In early March 2023, Song captured in the surveillance footage a graceful Chinese merganser circling around the tree hollow.

The rare, beautiful duck has existed for over 10 million years, which is why the birds are often referred to as "living fossils with wings".

The species has been on the Red List of Threatened Species of the International Union for Conservation of Nature, and it's also under first-grade State protection in China.

Its presence in a wetland is indicative of the area's ecological health, as the birds require a clean aquatic environment and generally choose to live near unpolluted bodies of water and in nature reserves.

"The past years' experience told me that the precious bird was going to settle here," he said. "However, worries followed amidst the joy. If the Chinese merganser occupied the sole natural nest, where would the mandarin duck family find their shelter?"

A bold idea brewed in his mind to build more homes for the increasing bird families, which also received support from his wife.

He spent over 10,000 yuan ($1,391) from the family's savings building three artificial nests in 2023 and another 18 in 2024, all equipped with monitoring equipment.

So far, the warm artificial bird nests have welcomed 10 pairs of mandarin ducks and four white-cheeked starlings to settle down. The Chinese merganser Song monitored has hatched eggs for three consecutive years.

"The Chinese merganser hatched 10 baby birds in 2023 and 2024, respectively," he said. "It was observed in the Yalu River Basin on March 9 for the first time this year. From March 27 to April 12, it laid 12 eggs in the nest and after 35 days' hatching, all the baby birds emerged from the shells."

As the last baby bird leaped out of the nest and staggered toward the rippling river on May 16, Song could not help shedding tears.

Over the past seven years, he has saved over 100 birds and animals in distress, including 31 mandarin ducklings orphaned due to their mothers' death, 11 mallard ducks, and a Common Kestrel that mistakenly ingested a poisonous insect.

Han Junhong in Changchun contributed to this story.

Contact the writers at zhouhuiying@chinadaily.com.cn