The legendary "bird without feet" turns out to be right next to us!

The beginning of autumn has passed and the weather has turned slightly cooler. Just as we were lamenting the change in the weather, a kind of bird quietly embarked on its journey. The empty nests showed that these lovely elves were already heading towards Africa.

This bird that "loves to travel" is the Beijing Swift. From April to July every year, the Beijing Swift will come to Beijing from afar, lay eggs, hatch and raise chicks in about 90 days, and then go to Africa when the weather turns cooler , waiting to meet everyone again in the spring of next year.

Beijing swifts flying in the sky (Photo source: globaltimes.cn)

01

The "pilot" who almost never lands

Speaking of the Beijing Swift, you may not be very familiar with it, but when it comes to Nini, one of the "Fuwa" of the 2008 Beijing Olympic Games, everyone must be familiar with it. In fact, the prototype of Nini is the Beijing Swift .

The Beijing Swift (Apus apus pekinensis) is actually a subspecies of the Swift (Apus apus) .

In 1870, British naturalist Robert Swinhoe discovered that the Beijing swifts were different in morphology from the European swifts, so he called them the Beijing subspecies of the common swift, also known as the Beijing swift.

Beijing Swift (Photo source: pbase.com)

Beijing urban area is the main distribution and breeding ground of Beijing swifts , while there are relatively few in remote suburban counties and districts.

Because swifts are climbing birds, they need to build nests in mountain crevices or caves. Since Beijing moved its capital to Beijing in the Ming Dynasty, a large number of buildings have been built. The beams, purlins and rafters in these buildings have formed artificial caves, which are safer and more comfortable than in the wild. Over a long period of time, swifts have gradually become accustomed to building nests and breeding in Beijing.

Whether it is the European common swift or the Beijing swift, they leave their habitats in July every year and migrate to the central and western regions of Africa. Although they travel long distances to Africa, surprisingly, their feet may never set foot on African land.

They forage for food, mate, and obtain nesting materials in the air. They may land on branches or houses, but they will not actually land on the ground because their legs are short and their wings are long. Once they land on flat ground, they cannot use the power of their legs to take off again .

If they are not rescued, they will almost certainly die, so the swift is also called the "bird without feet". Its genus name and specific epithet "apus" come from the Greek word "apous", which means "without feet". I have to sigh that taxonomists are really good at naming.

The little feet of a swift (Image source: merseysiderg.org.uk)

In order to find out how long swifts stay in the air, several scientists from Lund University in Sweden installed lightweight data recording devices on 19 swifts in 2013 and recaptured them a year or two later. The researchers used the acceleration, body posture and other data recorded by the device to determine whether the swifts were flying or resting at the time.

Data shows that some swifts almost never stop moving during their long migration. For example, scientists found that between September 2013 and April 2014, a swift only rested for four nights in February; in the second year, the swift never rested for a whole night, specifically, it only rested for two hours. According to scientists' calculations, the time spent by swifts on rest during migration accounts for only 0.64% of the entire journey .

Swift (Image source: newscientist.com)

Such long flight times mean that swifts must be able to sleep while flying, and while there are no sensors small enough to monitor brain wave changes in swifts during flight, studies on frigatebirds have shown that birds can indeed sleep during flight.

Perhaps, swifts are like frigatebirds, sleeping for a few seconds each time and then regaining their spirits. Perhaps only in this way can they cross thousands of mountains and rivers and complete this long-distance journey of tens of thousands of kilometers!

02

This is a journey of more than 30,000 kilometers.

In fact, although people have long been curious about the flying ability and migration routes of swifts, swifts are so small and light, weighing only 30-40 grams, that any device that is slightly heavier will affect their normal flight.

A common swift wearing a band (Image source: commonswift.org)

So earlier, people tried to understand the flight tracks of swifts through rings (special metal leg rings with codes). But as we all know, swifts fly fast and far, and the greatest role of rings may be used to estimate the fidelity of swifts to their breeding grounds. If you want to know where they fly and what places they pass through, you have to find other ways.

The photosensitive locator is a new method discovered by scientists in recent years. The net weight of the locator is only 0.65 grams, and the impact on the flight of swifts is relatively small. The photosensitive element on the locator will record the solar altitude angle and the time of sunrise and sunset.

After scientists recovered the locators, they were able to use a set of methods to calculate the relatively accurate migration path of the swifts based on the recorded data.

Photosensitive locator (Image source: References)

Look at the swifts equipped with light-sensitive locators. Do they look like they are carrying a small schoolbag? When the swifts return to their original habitats to breed next spring, scientists can recover these locators and determine where they have been and where they have stayed!

A 2012 paper published in the journal PLOS ONE looked at the migration paths of the European common swift, a species of bird that flies south across Europe and then southwest across the Western Sahara Desert toward the Congo Basin.

Migration trajectory of the European common swift (Image source: References)

Compared with these European relatives, the Beijing Swifts should have to travel greater distances to reach their wintering grounds, and this is indeed the case.

In May 2014, the China Birdwatching Association put locators on 31 Beijing Swifts. In May of the following year, they recovered 13 Swifts wearing locators. Although the number is small, it can still provide us with a lot of effective information about the migration of Beijing Swifts.

This work continued until 2018, and scientists recovered a total of 25 light-sensitive locators, five of which had two years of tracking data. Based on the data provided by these locators, scientists mapped the migration routes of Beijing swifts to Africa for wintering and then returned to Beijing from Africa . The relevant article was published in the journal "Sports Ecology" in July this year.

The left one is the path to Africa for wintering, and the right one is the path back to Beijing in spring.

Image source: References

Amazingly, this migration covered a distance of almost 30,000 kilometers .

Specifically, the Beijing swifts leave Beijing in July and take more than three months to reach their wintering grounds on the South African plateau. This half of the journey is almost 15,000 kilometers, which means that these swifts have to fly more than 130 kilometers every day.

The following spring, the Beijing Swifts will return from Africa to meet everyone. This distance is also not short, but the Beijing Swifts are in a hurry to come back to breed, and their flying speed is relatively fast, so they can complete the return journey in about two months.

So there was a saying at that time that a Beijing swift could fly a distance that exceeded the average distance between the earth and the moon (384,403.9 kilometers) before dying of natural old age (based on a lifespan of 14 years).

Swifts are truly amazing creatures!

03

Beijing Swifts Need More Protection

However, you may not know that this elf bird, which belongs to the sky all its life and has been crossing thousands of mountains and rivers, was even on the verge of extinction more than a decade ago.

According to the China Green Times, the Beijing swift population reached its peak in the early 20th century, with a population of about 50,000. However, with the acceleration of Beijing's urbanization process, by the beginning of this century, there were only about 3,000 swifts left in Beijing, and the number continued to decline in the following decade. In 2014, statistics from the Beijing Bird Watching Association showed that there were only 2,700 swifts left in Beijing .

Beijing Swifts living with humans (Photo source: osme.org)

Beijing swifts are accustomed to building nests and breeding on man-made buildings. However, in recent decades, there have been fewer and fewer buildings in Beijing, such as city walls, temples, and ancient pagodas, that are suitable for Beijing swifts to build nests . This is the key reason for the sharp decline in their numbers.

Not only that, after the 1980s, the protection of ancient buildings by various units also affected the survival of swifts. People believed that swifts' feces might corrode wood and paint, so they set up protective nets under the eaves of ancient buildings. Now the swifts are unable to return to their homes, and their survival is in jeopardy.

The plight of swifts has made bird lovers and experts very anxious. After much deliberation, they decided to provide swifts with a new nesting place. In 2008, the Swift Tower was erected in Beijing Olympic Forest Park . However, the embarrassing thing is that the tower is not inhabited by swifts, but by sparrows.

In 2018, in order to understand whether swifts would have adverse effects on ancient buildings, a project entitled "Research on Ancient Building Protection and Urban Ecology - Taking Beijing Swifts Living on Zhengyangmen as an Example" was officially launched.

According to the data obtained from the project, the pH value of swift feces and nests is neutral, and no fungi, bacteria, or microorganisms in the feces and nests have been found to degrade or corrode wooden building components. In other words, swifts do not have a substantial impact on ancient buildings . In this regard, experts believe that it is better to protect the ancient buildings where swifts can build nests than to build new nests.

Just when everyone was at a loss, experts and volunteers discovered that Beijing swifts were also adapting to the changing Beijing. Their nesting sites spread outward from ancient buildings, under overpasses, on the eaves of antique buildings, and in caves created by old and damaged modern buildings.

Recent data shows that the population of swifts in Beijing has increased to more than 10,000. We hope that in the future, this bird that lives in Beijing will still be able to fly freely in the sky of Beijing!

Author:EVEE

References:

Hedenström, A., Norevik, G., Warfvinge, K., Andersson, A., Bäckman, J., & Åkesson, S. (2016). Annual 10-month aerial life phase in the common swift Apus apus. Current Biology, 26(22), 3066-3070. Morganti, M., Rubolini, D., Åkesson, S., Bermejo, A., de la Puente, J., Lardelli, R., ... & Ambrosini, R. (2018). Effect of light-level geolocators on apparent survival of two highly aerial swift species. Journal of Avian Biology, 49(1), jav-01521.

Åkesson, S., Klaassen, R., Holmgren, J., Fox, JW, & Hedenström, A. (2012). Migration routes and strategies in a highly aerial migrant, the common swift Apus apus, revealed by light-level geolocators. PloS one, 7(7), e41195.

Zhao, Y., Zhao,

This article is produced by Science Popularization China and supervised by China Science Popularization Expo