The nest of Beijing swifts at Zhengyangmen is empty, and the "epic migration" begins again

The Beijing Swift is the only wild migratory bird named after Beijing. Why did their numbers drop so dramatically? Why do they have to make an "epic migration"? How does Beijing build a comfortable home for them?

Written by Li Peng, Photo and text edited by Chen Yongjie

Photo courtesy of the "Beijing Swift Tracking Project" team

Interview experts

Zhao Xinru (Associate Professor of Beijing Normal University, Professional Consultant of China Birdwatching Society)

Liu Yang (Professor of School of Ecology, Sun Yat-sen University)

Zhao Yanyan (Assistant Researcher, Guangxi Academy of Sciences)

Fu Jianping (Former President of the China Birdwatching Society, Swift Banding Volunteer)

From April to July every year, you can always see flocks of swifts hovering in the sky in Beijing, with the wind blowing through the eaves and the swallows singing. On July 24, people found that the nest of Beijing swifts on Zhengyangmen was empty, which means that they have bid farewell to Beijing and started an "epic migration" of about 30,000 kilometers.

The Beijing Swift is the only wild migratory bird in the world named after "Beijing". It likes to breed and live under the eaves of ancient buildings on the central axis of Beijing. It is a common bird in Beijing and the prototype of "Nini", one of the mascots of the 2008 Beijing Olympic Games.

But around 2000, due to various reasons, people found it difficult to find Beijing Swifts in Beijing. Fortunately, with the continuous improvement of Beijing's ecological environment and the increase in protection efforts, it is estimated that the population size in Beijing has reached more than 10,000.

▲On July 12, at the Zhengyangmen Tower, swifts were flying lightly beside the eaves and brackets (Photo source: Xinhua News Agency)

Recently, an 8-year tracking study on the migration behavior of Beijing Swifts was published in the international journal "Sports Ecology", which accurately revealed the ecological laws of Beijing Swifts' migration for the first time. Why do Beijing Swifts migrate 30,000 kilometers to Beijing to reproduce? What touching stories are there in tracking the migration of Beijing Swifts?

The Beijing Swift has existed in Beijing for a long time. No one can tell exactly how long its history is. In 1870, the famous British naturalist Robert Swinhoe collected a swift in Beijing and found that it was not quite the same as the European species recorded previously. He added a subspecies name (Apus apus pekinensis) to the original species name (Apus apus), calling it the Beijing subspecies of the common swift, which literally means Beijing Swift. The Beijing Swift is called "House Swallow" by old Beijingers because it lives in tall ancient buildings. However, this bird is still not well known to the public for more than 100 years. Some residents of old Beijing city confuse it with the house swallow, and no one knows about the legendary journey it performs every year.

Protecting ancient buildings but accidentally hurting swifts

After the 1980s, Beijing's ancient buildings ushered in a "spring" of protection, and many tall ancient buildings have been carefully repaired. In order to prevent bird droppings from corroding the paint and wood, the cultural relics unit adopted the advice of experts and set up bird-proof nets under the eaves of the ancient buildings.

It was originally an initiative to protect ancient buildings, but what was unexpected was that this move was a "disaster" for the Beijing swifts that rely on ancient buildings to build nests and raise chicks.

In the spring of the following year, when many swifts that had spent the winter in other places returned to Beijing, they found that the caves where they once built their nests could no longer be found or entered, so they had to look for other places to breed.

"We just started counting the number of Beijing swifts within Beijing's Fifth Ring Road and found that there were only three to four thousand," said Zhao Xinru, an associate professor at Beijing Normal University and a professional consultant to the China Birdwatching Society, who has long been engaged in bird protection in Beijing.

▲The first tracking and banding of swifts in Beijing in 2014 was successfully completed (Photo by Wang Yuansheng)

Zhao Xinru analyzed that the change in Beijing's urban habitat is an important reason for the sharp decline in the number of Beijing swifts. The demolition of city gates, city walls and old houses, the reduction of ancient towers and temples, etc., have caused drastic changes in the living environment of Beijing swifts. The change in the nesting and breeding conditions of swifts is one of the basic reasons for the decline in their numbers.

After losing their habitat, the number of Beijing Swifts in Beijing decreases rapidly every year, and many people have begun to appeal and campaign to save the Beijing Swifts.

Rebuild a new nest or protect the old one?

The plight of Beijing swifts has made swift lovers very anxious. "Their nesting sites are gone, why don't we build them a 'new home'?" Some people who like Beijing swifts have put forward their own ideas. On the eve of the 2008 Beijing Olympics, Beijing Olympic Forest Park built a Swift Tower. This tower was advocated by environmentalists and designed by Tsinghua University. The tower is 20 meters high and has 2,240 artificial nest boxes for swifts. The park also hopes to provide a new home for Beijing swifts through artificial attraction.

However, the Beijing swifts did not settle down in the houses specially built for them, but instead became the cozy nests of many sparrows. In Zhao Xinru's opinion, this should be largely related to the unscientific design and attraction methods of the swift tower.

There are fewer and fewer places to live, so why don't the swifts like the "homes" built by people? Many volunteers can't figure it out. In fact, it is not difficult to understand. For thousands of years, Beijing swifts have been accustomed to the ancient buildings in Beijing. The "new home" built by volunteers does not meet their wishes.

But there are exceptions. In order to better protect Beijing swifts, the Beijing Zhengyangmen Management Office began to try to provide swifts with straw-woven artificial nest trays on the ceiling of the city tower in 2019. Two sizes, one the actual size and the other twice as large, were selected and placed in locations where swifts often appear for them to choose. As a result, a pair of swifts were found that year to have chosen an artificial nest tray, and after doing "internal decoration", they began to lay eggs. This successfully helped swifts complete their breeding activities using artificial nest trays.

The experiment of building artificial nest boxes for Beijing Swifts is still going on. The China Birdwatching Society and the China Garden Museum have cooperated to hang some new artificial nest boxes in the Beijing Garden Expo Park. This nest box refers to the nest box plan of the common swift nominate subspecies made by the Germans, but because the Beijing Swift is larger, the size of the nest box has also increased accordingly. In order to attract Beijing Swifts, the China Garden Museum also attracts them by playing high-fidelity swift calls. Guan Xueyan, president of the China Birdwatching Society, has also visited the site many times to discuss and study technical measures to attract swifts with the museum. Zhao Xinru is very optimistic about this project, but he believes that it may take three to five years or even longer to see the effect.

"Instead of building new houses, it is better to protect old houses," said Fu Jianping, former president of the China Birdwatching Society and a volunteer for swift banding. She believes that it is very important to strike a balance between protecting ancient buildings and swifts in Beijing, which requires the support of scientific research.

In recent years, there have been debates about the contradiction between bird habitats and the protection of ancient buildings, but there has been no quantitative scientific research data to support it. To this end, the Beijing Zhengyangmen Management Office has set up a special scientific research team to extract the DNA of microorganisms in the nests and feces of Beijing swifts and quantitatively analyze their impact on the brick and wood ancient buildings of Zhengyangmen. The final test results showed that the pH value of swift feces and nests was neutral, and no fungi, bacteria or other microorganisms in the feces and nests were found to degrade or corrode the wooden components of the building. This proves that swift feces and nests do not have a substantial impact on wooden ancient buildings.

"Such research results show that Beijing swifts do not cause much harm to ancient buildings," said Fu Jianping.

The continuous loss of habitat for Beijing swifts once worried Zhao Xinru and many volunteers. Traditional nesting places are becoming fewer and fewer, and they don't accept the artificial nest boxes built for them. What should they do?

Just when the volunteers were at a loss, some bird-watching enthusiasts brought good news: swifts appeared under some modern buildings in Beijing and under overpasses such as the Tianning Temple Bridge, Jianguomen Bridge, and Guomao Bridge. It turned out that the Beijing swifts were constantly adapting to Beijing's rapidly changing environment and they had found some new nesting habitats.

Surveys on Beijing swifts conducted by the Beijing Wildlife Rescue Center in recent years have also shown that the nesting sites of Beijing swifts are gradually spreading and shifting from ancient buildings to modern buildings, and they are gradually adapting to the changes in the city of Beijing.

Fu Jianping and other volunteers have observed for a long time that the adaptation of Beijing swifts to modern buildings such as overpasses is a gradual process. In the early stage, there were only about 10 Beijing swifts under an overpass, but in recent years, observations have found that some overpasses have 100 to 300 Beijing swifts living there, or even more.

▲The modern building's antique-style roof provides a nesting and breeding environment for Beijing swifts (Photo by Fu Jianping)

"When observing the Beijing swifts under the overpass, we couldn't take pictures of their nests in the caves, but some photos and videos recorded the process of them drilling holes and clinging to the bridge piers," said Fu Jianping.

▲In 2017, a large group of swifts were recorded breeding under the Guang'anmen South Bridge (Photo by Cui Yaqi)

In addition, some other modern buildings have also begun to be used by Beijing swifts. In the 1950s, many 6-story buildings with large roofs were built in Beijing. The underside of the eaves protruding from the edge of the roof was often made of wooden slats and hemp ash. As the hemp ash fell off and the slats became old and damaged, some caves appeared, which became the shelters of many Beijing swifts.

▲Beijing swifts build nests and reproduce in caves of ancient buildings (Photo by Zhang Qianyi)

However, Fu Jianping still suggested that some modern buildings in Beijing, especially those imitating ancient buildings, should leave some space for Beijing swifts to live in when they are designed. "Some imitating ancient buildings are just painted in the colors of ancient buildings. The colors are imitating ancient buildings, but the structure of the eaves is not composed of mortise and tenon joints, purlins, and rafters, but reinforced concrete eaves, with almost no caves and gaps, so there is no cave environment for Beijing swifts to choose nesting sites."

Tracking the migration of 25 Beijing Swifts

Zhao Xinru was relieved by the Beijing swifts' ability to adapt to modern urban buildings. The next step is to uncover the migration routes behind them.

Before 2015, the scientific community still did not know the migration route of the Beijing Swift. Some speculated that after leaving Beijing, they would fly over the Himalayas to the Indian subcontinent, while others believed that they flew along the eastern coastal areas of China to Southeast Asia.

The migration research of Beijing Swifts is not only a macroscopic study, but also involves microscopic research in molecular biology. For example, it is difficult to identify the gender of Beijing Swifts. It is difficult to distinguish between male and female based on their appearance. The best way is to capture Swifts, collect their blood and use DNA to identify their gender. Knowing their gender, we can track and study the different flight strategies of male and female individuals.

Zhao Xinru began to form a team to track the migration of Beijing Swifts. Team members included Liu Yang, a professor at the School of Ecology at Sun Yat-sen University who had participated in the Beijing Swift survey project, Zhao Yanyan, an assistant researcher at the Guangxi Academy of Sciences, Fu Jianping, the former president of the China Birdwatching Society who had extensive experience in banding Beijing Swifts, and many volunteers who love Beijing Swifts.

To track the migration route of Beijing Swifts, the first thing to do is to select a tracking instrument. Since Beijing Swifts spend most of their lives in flight, even mating and hunting are done in the air, they cannot be captured in foreign lands and have their migration information recorded through marking rings like many other birds when they are not in their breeding grounds. In addition, GPS devices have not been miniaturized at low cost in recent years, and there is no way to install them on Beijing Swifts, which weigh only 30 to 40 grams.

Later, micro-photosensitive locators gradually came into the research team's view. This is a low-consumption recycling device that records light intensity and locates and tracks based on the changes of day and night. It can relatively accurately depict the migration path of Beijing swifts.

▲The first step - net capture (Photography by Wang Yuansheng)

▲The second step - banding (Photo by Zhang Weimin)

▲The third step - wearing (Photography by Zhang Weimin)

▲Step 4 - Sampling (Photography by Zhang Weimin)

It is not an easy task to select the right Beijing Swifts to wear micro-photosensitive locators. First, you have to choose the banded Swifts that have migrated and flown back to Bafang Pavilion (Beijing Swifts are loyal to their original nest sites and are easy to be recovered next year). Then put the photosensitive locators on them. In the specific operation, the research team and volunteers have to arrive at Bafang Pavilion at two o'clock in the morning to set up the nets every time they capture them. After wearing the photosensitive locators, the research team hopes that these cute little creatures can fly back smoothly the next year. However, due to various reasons, not every Swift wearing the locator can be recovered. Some did not return to the Summer Palace, some may have died naturally on the way, and some have not been recovered yet.

▲Step 5 - Release (Photography by Zhang Long)

In 2015, the research team released 66 swifts equipped with light-sensitive locators and eventually recovered 25. The tracking results were jaw-dropping: it turned out that Beijing swifts perform "epic-level" flights every year, flying all the way to southwest and southern Africa, with a round trip of about 30,000 kilometers.

Data shows that the autumn migration of Beijing Swifts mostly begins in mid-July. They leave Beijing, head northwest into Mongolia, then west into northern Xinjiang, and enter Central Asia from the Junggar Basin. They cross the Red Sea in mid-August and arrive in central Africa in early September, making a short-distance migration of 40 days in the Congo Basin or adjacent areas. They then slowly head south and finally reach their wintering grounds - the South African plateau at an altitude of about 1,000 meters - in early November. The entire journey is 14,733 kilometers and takes 111 days.

▲Autumn migration route map of 25 Beijing Swifts. The gray shaded area is where the Beijing Swifts breed (Photo courtesy of Zhao Yanyan)

After a 100-day wandering during the winter, the Beijing Swifts began to move northward rapidly in mid-February of the following year, staying in the eastern Congo Basin for nearly a month. They then turned northeast and left Africa in early April, traveling day and night, returning to Beijing in late April. The entire journey was 13,572 kilometers and took 64 days. During the entire round-trip migration, the Beijing Swifts' flights covered 37 countries in Asia and Africa.

"Revealing the secrets of swifts' lives through modern scientific and technological means also makes me feel that it provides important information for protecting this bird." Zhao Yanyan said that she hopes the research can provide a more scientific basis for better protecting Beijing swifts.

There are more secrets for us to uncover.

In addition to revealing the amazing migration route of the Beijing Swift for the first time, researchers and volunteers have also learned more secrets of the Beijing Swift through long-term observation.

It was observed that Beijing Swifts usually lay 2 to 3 eggs per nest. The eggs are oblong, nearly pure white and without spots. The male and female birds take turns to incubate them, and the eggs hatch in about 21 to 23 days. Healthy chicks are naked when they are born, with only a small amount of down feathers, which are flesh-red in color. Their eyes are large in proportion to their heads, so they are affectionately nicknamed "Big Eyed Cute". The little guy is a late-hatched chick. When he is born, his eyes are closed and his parents need to keep him warm with their bodies. About two days later, the chicks begin to be fed by their parents; after a week, they begin to grow some feathers; after 15 days, the feathers are basically grown, and they begin to flap their wings in the nest and learn to fly; they can leave the nest in about 30 days. After leaving the nest, the young birds no longer return to the nest. It was observed that they would gather in the airspace near the nest to learn to fly and exercise endurance, and then embark on the migration journey with the adult swifts.

In order to understand the social methods of Beijing swifts, Guan Zhanxiu, director and deputy research librarian of Beijing Zhengyangmen Management Office, and Hu Bin, head of the Cultural Industry Department of the office, cooperated with technology companies in 2021 to obtain the calls of swifts at different stages through a combination of cameras and on-site microphones. In this way, they understand the specific "language" and communication methods of Beijing swifts, and provide conditions for guiding them with artificial technology in the future. They also plan to spend three years collecting and analyzing the social relationships between swifts, such as the choice of mates, the competition for nests, and the re-combination of widowed families.

In Zhao Xinru's opinion, the scientific research and tracking of Beijing Swifts has just begun. Although many secrets of Beijing Swifts have been learned through micro-photosensitive locators, more secrets are yet to be revealed. For example, how do such small birds complete a 30,000-kilometer migration? How do they navigate and why do they migrate along the same route every year? How do young swifts born in Beijing, who have no migration experience at all, successfully fly to their wintering grounds in southern Africa?

▲Teacher Zhao Xinru (third from right) promotes the event to tourists (Photo by Zhang Long)

Zhao Yanyan, who is in charge of the micro-photosensitive locator at the Guangxi Academy of Sciences, said that micro-GPS devices are constantly developing and their costs are constantly decreasing. In the future, the research team may closely combine micro-GPS devices or Beidou devices with micro-photosensitive locators, so that the research on the migration routes of Beijing swifts will become more accurate.

Next, they will continue to cooperate, and the research team will use genome sequencing technology to decipher the genetic code behind the migratory miracle of the Beijing Swift. It is believed that through these efforts, the secrets behind the extraordinary athletic ability of the Beijing Swift will be gradually revealed. They believe that the Beijing Swift is also an ideal species for studying animal migration and navigation.

The research team will also conduct special research on Beijing Swifts from an ecological perspective, so as to gain a deeper understanding of their population size, age structure, reproductive characteristics, food habits, etc., to provide a basis for the next step of protection.

Let’s see them again in Beijing next April!

Tips

Distinguishing between Beijing Swifts and House Martins

▲Beijing Swift (Photographer: Zhang Long)

The Beijing Swift belongs to the order Noctiluca. It generally weighs around 30 to 40 grams, is 18 centimeters long, and has fine white longitudinal stripes on its chest and abdomen.

The legs of the Beijing Swift are not only very short, but the four toes on each leg point forward, forming a foretoe type.

When flying, the Beijing Swift flies with its wings fully spread out, forming an arc, shaped like a curved sickle.

The house martin belongs to the order Passeriformes, weighing about 14 to 22 grams, and about 15 centimeters long. The feathers on the back are black and shiny, and the abdomen is white. The house martin has three toes facing forward and one toe facing backward. When flying, the house martin flies with its shoulders hunched.