Study shows intercontinental flight paths of the Beijing Swift for first time

In late spring, Yuan Xuejun, who works in an office near the Zhengyang Gate in Beijing, loves hearing the sharp, clear notes of birds in the sky.

She is frequently distracted from her work by their chirping, and takes numerous photos of them against the backdrop of the gate.

Each year, the birds appear in the spring, before migrating in the autumn.

Yuan, 56, an associate researcher at the Beijing Central Axis Heritage Protection Center, said: "I wondered where they headed for the winter. I am so grateful for the chance to fully appreciate the birds and enjoy their boundless energy."

In late June, a study published in the international journal Movement Ecology showed the migration routes and preferred habitats of migratory birds for the first time.

Yuan is enchanted by the Beijing Swift (Apus apus pekinensis), the only wild migratory avian species in the world named after the Chinese capital, and a subspecies of the common swift (Apus apus).

These birds travel about 15,000 kilometers annually to spend the northern winter in southern Africa, covering the same distance when they return to Beijing to build nests and start breeding.

The swifts, which are 16 to 18 centimeters long, fly fast and cover long distances. They rarely land during migration, and perform the round trip of 30,000 km every year, passing over 37 countries and regions.

According to the study, Beijing Swifts begin their autumn migration in the middle of July－leaving the city after breeding.

They fly northwest to Mongolia, then west over Xinjiang Uygur autonomous region, the Junggar Basin－a large sedimentary area in northwestern China－and then enter Central Asia.

Around Aug 16 every year, the birds cross the Red Sea and head toward Central Africa. They reach the eastern Congo Basin in early September, where they remain for about one month, before flying south to reach the Southern African Plateau in early November. They stay there for about 100 days.

Liu Yang, corresponding author of the study and professor of life sciences at Sun Yat-sen University in Guangzhou, capital of Guangdong province, said, "To reach Africa, the birds fly in the shape of a parabola.

"The research also suggests that they adapt well to semi-arid areas and have a preference for hot air currents. One of the major reasons for this is that countless insects－the birds' primary source of food－abound in relatively dry regions."

Liu said that rather than heading straight to the hot and humid south, the swifts take a "labor-saving route" by first flying north and then northwest due to their dietary habits.

The return route for the spring migration is almost identical. The birds arrive in the eastern Congo Basin in mid-February from the Southern African Plateau, staying for about a month before crossing the Red Sea. They leave Africa in early April.

Flying almost nonstop, the swifts return to their breeding area after arriving in Beijing from about mid-April to mid-May.

Difficult task

Understanding the behavior of birds is important in protecting migratory species, and the difficult task of tracking Beijing Swifts is made easier by devices known as light-level geolocators, which are carried by the birds.

During the breeding season from 2014 to 2018, a research team from Beijing Normal University and Sun Yat-sen University comprising ornithological experts and volunteers from Sweden, Belgium and the United Kingdom conducted fieldwork at the Kuoru Pavilion in Beijing's landmark Summer Palace.

Zhao Xinru, an ornithologist from Beijing Normal University and a lead researcher for the study paper, said he led the team when it entered the Summer Palace at about 2 am. Fine nets were set up around the Kuoru Pavilion between 3 am and 4 am.

"We were pressed for time as we carried out fieldwork at this ancient imperial garden. As this scenic spot is visited by large numbers of tourists, we had to strictly abide by the rules to protect ancient architecture at the Summer Palace and complete our fieldwork research during the early hours to avoid inconveniencing visitors," Zhao said.

"Five nets were set up in the Kuoru Pavilion, with each one precisely positioned and designed to protect the structure and ensure the birds were not harmed when captured."

After being captured, randomly selected swifts were fitted with the tracking devices by the volunteers.

"We take particular care to ensure that just the width of a pencil separates the devices and the birds' bodies so that the swifts are comfortable and can fly freely," Zhao said.

Liu said a geolocator weighs just over 1 gram, and according to international standards the devices cannot exceed 3 percent of the bird's weight. When tagged to the swifts, the geolocators track sunrise and sunset and record light intensity.

"Dawn and sunset vary according to location, and the devices give us the opportunity to determine the swifts' approximate position based on the birds' circadian systems," Liu said.

Data from small electronic chips installed in the geolocators is downloaded and read by software, according to Liu. After an initial estimate, the approximate migration routes of the swifts are outlined.

By 2018, researchers had successfully retrieved data from 25 swifts, and 66 of the birds had been fitted with geolocators.

Stopover sites

It was widely believed that Beijing Swifts migrated directly to destinations without stopping, but the research results showed otherwise.

Swifts typically travel more than 250 km on average each day. They are considered to have reached a stopover site if they do not travel any farther than 500 km for at least three days, the study found.

Liu said: "The Beijing Swifts visited two to six stopover sites during their autumn migration, while remaining at one or two such sites in the spring migration, according to the observed data. We presume the birds spend more time accumulating fat reserves or flying locally during their time at stopovers so that they can manage a long migration."

The three main stopovers for the Beijing Swift are the Congo Basin and its surrounding areas, the southwestern coast of the Red Sea, and the Caspian Sea's southern coast.

Ancient buildings

In spring, flocks of Beijing Swifts hover in the sky over the capital. They nest in the city's ancient buildings, including the Beihai Park pavilion, the Palace Museum and the city's ancient gates.

The birds have four short, forward-facing claws. To become airborne, they extend their wings to the full, retracting their claws in flight.

Zhao, the ornithologist, said: "This species flies nearly all its life, except during the breeding season. The swifts' forward-facing claws are suitable for clinging to cracks in cliffs and gaps in ancient buildings and walls.

"In Beijing, the roofs of ancient architecture provide ideal wooden perches for the birds, which they prefer due to the layer of thermal insulation that exists in wooden structures."

In 1870, the Beijing Swift was first observed in the capital by British naturalist Robert Swinhoe, before becoming a symbol of the city's avian diversity.

In recent years, surveys on the birds' numbers carried out by the Beijing Wildlife Rescue and Rehabilitation Center indicated that their nesting locations were increasing, with the swifts showing a preference for nesting in tall buildings.

Shi Yang, director of the center's wildlife rescue department, said the birds now nest widely across the capital, while in 2008, they were only found at 40 nesting locations.

Zhao said artificial nesting boxes should be provided for the birds at suitable locations throughout Beijing, and sounds of them chirping should be broadcast near artificial caves to encourage the birds to build nests.

Citizen science

Several decades ago, a large number of volunteers from civil groups in China first took part in observing and banding birds.

As they have become more involved in this work, the volunteers have turned their hobby into a type of citizen science to help ornithological research and protect migratory birds.

One of the volunteers, Fu Jianping, 66, has been banding birds for 24 years as an important way to study migratory species. This work generally involves placing a metal ring with an identification number on a bird's foot.

"It is exacting work," Fu said, adding that to prevent the birds dying of dehydration or isolation, every two hours the volunteers need to inspect the nets they put up during the day.

"If we hold a bird too tightly, we're afraid we will hurt it, but if we hold it too loosely, it might slip through our fingers," she said.

When a bird is recovered, relevant information about it is traced through the ring, and the location, date of discovery and other information are provided to the sharing data platform operated by bird-banding organizations.

Fu said, "In many countries worldwide, bird-banding is carried out by volunteers."

During the May Day and National Day holidays, instead of heading for a number of scenic areas, Fu always visits a location in Beidaihe, a picturesque coastal resort in Hebei province, where after being trained, volunteers place bands on birds.

After several years, the volunteers banding birds with Fu became highly proficient, but she said they might injure their fingers if the bands were not attached properly.

Research on the Beijing Swift is advancing as efforts from different sectors are stepped up.

Yuan, from the Beijing Central Axis Heritage Protection Center, said a study on the birds' living habits carried out in 2018 concluded that they used soil to build their nests, and that the feathers they left on the wooden architecture of the Zhengyang gate had no significant impact on the ancient structure.

After placing seven video cameras at the top of the gate to monitor the swifts' nests, Yuan and her colleagues observed that each bird usually laid two to four eggs. Their young hatched in about 21 to 23 days.

"Despite seeing the newborns every spring and summer, I still feel I'm not that familiar with them and that a lot of work needs to be done in order to fully research and protect the swift," Yuan said.

Zhao said priority should be given to research efforts, as genetic and ecological studies of the swifts are vital for their protection.

"More attention should also be paid to citizens' participation in the scientific research and conservation of the species in China," he said. "Scientific research and environmental protection can attract participation from people in different industries, which is also a positive driving force for the development of society.

"I hope that research on the Beijing Swift is only a beginning, and that more volunteers and citizens from various sectors will actively take part in observations and scientific studies of the species."