Despite being reluctant to see them go, Yang Wei still felt quite happy watching the two young birds she had cared for soar into the sky with their migratory flock that had returned for spring.

Yang, a 51-year-old photographer, had helped an injured Oriental white stork and its companion safely endure the extremely cold winter in Harbin, Northeast China's Heilongjiang province.

The International Union for Conservation of Nature has classified the Oriental white stork as critically endangered, with only about 9,000 remaining.

On Dec 2, Yang was taking photos of the sunrise near the Binbei Bridge of the Songhua River.

"There is a wastewater discharge outlet near this water area, and the treated wastewater maintains a relatively high temperature, so it does not freeze in winter," she said. "Wild ducks and other birds are always found on the unfrozen water surface, so I went there twice a week to capture photos of the birds."

As she was shooting, Yang saw a large bird fly out of the mist and land on the riverbank. Another bird arrived a moment later.

"I failed to take clear photos of them before they flew away," she said. "From that day on, I went to the area every day to search for them, but I only found some bird footprints on the shore."

It wasn't until Dec 10 that Yang and her photography friends finally got a clear view of the birds using a drone. "I determined that they were Oriental white storks because I had photographed some that were migrating before," she said. "Then I asked experts for further confirmation, and they agreed with me, which made us very excited. We had never seen Oriental white storks that should have migrated south wintering in Harbin."

Yang soon discovered that the smaller of the two storks had a gash on its right wing, and she reasoned that the injury, coupled with exhaustion, were why the birds were stranded in Harbin. Experts told Yang that the two birds were probably born only several months before and had likely just learned to fly.

As temperatures continued to drop, the water surface grew increasingly smaller, with no fish visible. "I thought it must be very difficult for the storks to survive the cold winter, so we decided to help them," Yang said.