Australian ornithologist Chris Hassel lives a life that's as migratory as the shorebirds he studies.

Every spring, the 50-year-old takes off from Australia and lands in China's Luannan wetland by Bohai Bay.

Since 2007, he has spent two months a year by the wetland in the coastal city of Tangshan, Hebei province, engaging a shorebird research program funded by Birdlife Netherlands, the World Wide Fund for Nature and Beijing Normal University.

"I love my job. It's really enjoyable to be close to the shorebirds and to nature," the bird researcher of 16 years says, smiling, in a Beijing restaurant, shortly before his return flight to Australia after finishing this year's work in Tangshan.

But it's not just fieldwork. He also must do a great deal of computer analysis and record population counts, Hassel says.

It's common for birds to migrate north to the Arctic to breed and then south for the winter. Studying migration routes is critical to ornithology, Hassel says.

There are eight major flyways globally. The East Asian-Australian Flyway (EAAF) is the most dynamic and is taken by the largest number of birds and the greatest variety of species.

Wetlands in Bohai Bay and Australia's Roebuck Bay - the two most important sites along the EAAF - are Hassel's main study locations.

His job includes banding the birds, especially the red knots - a flagship shorebird species - in Roebuck Bay, where they spend much of their lives, and tracking them afterward.

There are many methods for studying wild birds' lives. Banding is a more common technique because it's much cheaper than other methods, such as satellite tracking.

Ornithologists attach small, individually coded metal or plastic tags to birds' legs or wings to study various aspects of the birds' lives, including migration, mortality, population, territoriality and feeding behavior by recording re-sightings of the same individuals.

"Banding is simple and especially effective for the study of red knots, which have a relatively small size and normally appear in flocks, making them difficult to recapture," Hassel says.

In Luannan, Hassel, sometimes with his EAAF partners of the Global Flyway Network - a collaborative global organization of shorebird researchers and birdwatchers - record re-sightings of the color-banded birds with support from local ornithologists and volunteers.

The Global Flyway Network members at other EAAF sites also photograph and record their re-sightings of the banded birds, and update the information in a database that members share.

"In this way, we have an overall picture of their life cycles," Hassel says.

But up to 95 percent of the EAAF sightings are made in Bohai and Roebuck bays.

A large proportion of the birds banded in Australia pass through Bohai Bay. Among them, about 60 percent of the red knot population and 80 percent of its two subspecies - piersmai and rogersi - have made the narrow piece of mudflat in the Luannan their only stop, Hassel says.

"It's amazing for them to be so concentrated," Hassel explains.

"Industrialization in the area is a serious problem, particularly for these two subspecies, whose long-term futures rely on the remaining mudflat available. That's why it has such immense conservation value."

The red knots take an epic journey of about 10,000 km annually from Australia and New Zealand to the North Arctic.

"They fly nonstop, without eating or resting, for about six days all the way across the Pacific, burning only stored fat. Imagine that!" Hassel explains.

Then, the birds land in the mudflat in Luannan Wetland, which welcomes them with open resting places and rich food, such as abundant shellfish.

"They don't find the place by accident during such an extended flight," Hassel says.

"They know exactly where they are landing."

The red knots are highly specialized feeders and need large areas of inter-tidal mudflats to feed.

Their month-long stay allows them to recover the weight lost during their intense flights. Red knots can double their body weights with fat deposits during their stays at the mudflat.

"This period will decide whether they can arrive in the Arctic in summer successfully and find a mate to breed their next generation," he says.

But this critical migration stopover faces growing threats from industry-led reclamations, ocean traffic and oil installations. The rich wetland may be lost in two or three years.

"This is a problem that happens in China, but it's a global problem," Hassel says.

"We are asking for too much from nature. But there has to be a point when it won't work anymore."

He believes a consensus is needed to keep industrialization at a sensible level for the mudflat to survive.

"Local governments and businesses have always argued that the birds can just move somewhere else," he says.

"But these birds really don't have many alternatives."