A 'gas station' for migrating birds
Every spring and fall, the bar-tailed godwit flies between the Oceania the wintering ground and Siberia the breeding destination. Without pausing to feed, they hold the record for longest nonstop flight for a land bird.
Sitting in the middle of the East Asian-Australian bird migration route, Shanghai receives migratory birds such as waders twice a year.
As the weather starts to cool in the Northern Hemisphere, some birds have already taken off from the far north to reach the warmer wintering grounds. In the middle of their journey, many choose to make a stopover in Shanghai to rest and replenish their energy around Shanghai — the “gas station” on the migration route
Ma Zhijun, professor from the School of Life Sciences at Fudan University, researches migration ecology, habitat ecology and conservation ecology. Part of his job is to track the migratory birds passing by Shanghai.
“The migration distance of birds is different from other animals. They fly thousands of kilometers, some even fly 10,000 kilometers,” he told Shanghai Daily. “With scientific progress, we are now able to learn more about them.”
Bird migration has been a keen interest of Chinese researchers. In the past, the birds are color-flagged, something like an identification card with unique alphanumeric combination.
Once they are released, these birds can be captured and/or identified in a different location to gather information about their migration.
Drawing the lines after tracing the stopovers the birds make isn’t exactly accurate, as the birds don’t fly straight, and it could take them days or even months before reaching their destination. Now, scientists can install a small device on the birds to monitor them 24/7.
“We are focused on the migration of waders, because during their journey, they rely heavily on the tidelands and wetlands of Shanghai,” Ma said. “China’s land reclamation in the past few decades has caused habitat loss for waders, and it influences their migration.
“Without Shanghai the ‘gas station,’ the birds cannot reach the breeding grounds in spring and the wintering grounds.”
North of the Yangtze River estuary is an important resting place. Different species arrive at different times. Most stay 2-3 months between March and May.
A few years ago, Ma and his team installed a small tracking device on a great knot, a relatively large wader that breeds in northeastern Siberia and winters in Australia. When it reached the Yangtze River estuary in Shanghai, Ma discovered the bird only stopped for two days. Other trackers revealed similar results.
“From Chongming Dongtan’s perspective, the bird’s stay was very short — an average of two days. Some only stayed one day. It means that the Yangtze River estuary is only a temporary resting place or emergency safe haven when they encounter something bad,” said Ma.
The researchers then found the waders stayed an average of one month in the Yalu River region north of Bohai Sea. The longest stayed 57 days.
There, the waders could double their body weight in a very short period and prepare for the onward journey. Northeastern China has abundant food supplies — up to 10 times more than Shanghai.
“But even though the birds only stay briefly in Shanghai, it still matters,” Ma said.
For those flying five days and nights non-stop from Australia and traveling 5,000 kilometers, they desperately need to rest in Shanghai if they are flying into the wind.
The great knots can be observed every day from the end of March to the end of April, each staying one or two days.
For decades, research has largely depended on the identification rings attached to the birds’ feet to plot their migration. Even though the good old method requires capturing, inspecting and releasing the birds, it’s still significant in studying birds.
To start with, bird banding is much cheaper than modern hi-tech tools. One can learn where the bird is from and heading to easily while gaining much more information.
It’s also a great way to engage the public to help find the tagged individuals, says Ma. “China came late to the bird-watching trend,” he said. “There are many birders abroad who can help you gather information.
“In some countries, citizens can apply for a certificate to put identification rings on birds after taking training on proper methods. It also bonds people worldwide. And in the big data era, this kind of data is a gold mine for research.”
In China, bird banding is strictly monitored and few people outside the research field can participate.
In Hebei Province, a primary school teacher first started to help others putting identification rings on birds, and the bird banding center allowed him to do it independently soon after.
Modern technologies now include satellites, GPS and geolocator tracking, which provide much more detailed and accurate results that allow scientists to learn the exact migration routes.
GPS tracking is accurate to 10 meters and the satellite tracking is accurate to 100 meters.
Most species can wear tracking devices, which cannot exceed 5 percent of the bird’s body weight — 3 percent is preferred.
The smallest satellite tracker is about 1 gram, and the average is 3g, so birds heavier than 100g can wear them.
For the larger birds, acceleration sensor chips can also be added to learn whether they are in flight or resting on the ground.
Ma and his team has started the fall bird migration survey this month. His focus is whimbrel, a fairly large wader that weights around 300g, so the researchers use 9-10g trackers.
The response rate of modern tracking methods is much higher than the traditional bird banding, 60 percent compared with 10-20 percent, Satellite and GPS tracking also provide more detailed information.
“We are not seeing very obvious changes,” said Ma. “Some birds have changed their habits, like the light-vented bulbul which is usually seen in the south of Yangtze River is now observed in Beijing and northeastern China, the species distribution has changed.”
The number of migratory birds in Shanghai has decreased rapidly. A decade of research found a significant decrease in tideland and wetland in areas. Birds as an indicator of the health of the environment are also crucial to human development.
“When we study the different birds and their roles in different locations, we can have targeted measures like ensuring their safety in energy replenishment sites and providing a scientific basis for policy makers to implement the conservation policies,” Ma said.