When birds fly south, which “South” are they heading to?

Author: Yunhai Science Popularization

The article comes from the Science Academy official account (ID: kexuedayuan)

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Not long ago, Dayuaner saw a video: In a certain place in Northeast China, some birds that were illegally captured were rescued, but they missed the migration time. In order to help them go to the south for the winter, people drove them for 2,000 kilometers and then released them.

It seems like a very heartwarming story. But after watching the video, the courtyard worker couldn't help but have some questions in his mind: Is it really reasonable to send birds to the south by car? Where is the final destination of the birds' flight south?

One arrow deciphers the flight path of birds

Time goes by, and migratory birds always go from autumn to spring. Where do migratory birds go after autumn? Are the birds you see in spring the same ones you saw last autumn?

In order to get answers to these questions, humans have been thinking for more than two thousand years.

(Photo source: veer)

In the pre-Qin period in China, some people were curious about this. Especially the palace maids and princesses, who did not have much entertainment on weekdays, caught the swallows in the palace and tied colorful silk to them to observe whether they would come back the next year. Europeans in ancient Greece also thought about the phenomenon of birds disappearing in winter. Aristotle was inspired by the behavior of swallows carrying mud to build nests, and believed that swallows would dig holes in winter and hibernate in the holes, just like the toads we are familiar with. Even though no one had ever seen a swallow buried in the ground, due to the authority represented by Aristotle, most people at that time regarded this statement as a golden rule and never questioned it.

But the truth of nature will not change because of authority. With the progress of people's wisdom, evidence inconsistent with Aristotle's conclusions continued to emerge. In 1822, a very famous white stork in the history of bird migration research appeared near a village in Germany. The white stork is a common bird in Europe, and the legend of this white stork is that it has an arrow about 80cm long stuck in its neck, which can also be said to be a spear. This weapon originated from some tribes in central Africa. It was this arrow that made people know the trajectory of this bird: it crossed the Mediterranean in winter, arrived in Africa, was unfortunately shot by Africans, and flew back to Europe alive. After that, humans recorded 24 white storks with arrows in their bodies one after another. These unlucky and lucky white storks are called Pfeilstorch, which means "arrow stork" in German.

The first Pfeilstorch now exists as a specimen at the University of Rostock in Germany. In addition to its iconic significance in the history of bird migration research, these birds are also worth remembering for their perseverance - after being injured by an arrow, they still need to cross the Sahara and the Mediterranean from their wintering grounds in Africa, a distance of 3,000 kilometers back to Europe.

The first Pfeilstorch (Image source: Zoologische Sammlung der Universität Rostock)

Bird banding made easy

In 1899, a Danish teacher named Mortensen put aluminum rings with different numbers on the legs of birds to study bird migration. His method is similar to the ancient practice of palace maidens tying colorful silk to house swallows, but it is obviously more scientific and systematic. This marking method is called banding. It is simple and easy to use and quickly gained recognition from ornithological circles around the world. Special banding stations have sprung up like mushrooms after rain. In 1983, ornithologist Zhang Fuyun and others conducted the first bird banding work on the mainland at Qinghai Lake. At present, my country has become the country with the most banded birds in Asia.

The recovery of banded birds requires recapture, but the world is so vast. The recovery rate of banded birds is obviously not very high. It can reach more than 20% for large birds and even less than 0.1% for small birds. In the 1990s, ornithologists began to use flags to study migratory birds, especially waterfowl. Flags are tied to the legs of birds like metal rings, but the difference is that flags are colorful, and the colors and combinations of flags on birds banded in different regions are different. The location of the banding can be determined by the color combination of the flag, and if the code on it can be clearly seen, the individual can be confirmed. This method does not require recapture and recovery, and can be found using a telescope or telephoto lens, which is more efficient.

The combination of blue on top and blue on the bottom indicates that the Mongolian sand plover individual No. 00J was banded in Tiaozini, Jiangsu (Photo source: Haidongqing)

Global banding to map bird migration

Through the observation records provided by banding stations around the world and bird watching enthusiasts, we can know where birds come from, where they go, where they pass through, and outline their life trajectories. At present, there are 9 major migration routes in the world, 3 of which pass through my country.

The world's nine major migratory bird routes (Image source: Global Flyway Network)

Bird banding is a model of scientific research cooperation on a global scale. Even during the Cold War, academic exchanges could not be completely blocked. In 1964, Won Hong-gu, director of the Institute of Biology of the Academy of Sciences of North Korea, recorded a northern starling wearing a Japanese leg ring in Pyongyang. Due to the political environment at the time, the ornithological communities of North Korea and Japan could not communicate directly. Won Hong-gu's letter was forwarded to the Yamashina Ornithological Research Institute in Japan through Russia, hoping to know the detailed banding information of this northern starling. Japanese ornithologists checked the banding records based on the leg ring number C7655 and found that this northern starling was banded by Won Pyong Oh in Seoul, South Korea in 1963.

Careful friends may have discovered that both of these ornithologists have the surname Yuan, which is not accidental. There is a sad story behind this: Yuan Hongjiu is Yuan Bingyu's father. Because of the division of Korea, the family was separated in the war and had no news for 15 years. The recapture recovery rate of banded birds is very low, and the probability of father and son recapturing the same bird in two places is even smaller. Miraculously, the two learned that each other was still alive through a small leg ring. Unfortunately, they never met. Mr. Yuan Hongjiu passed away in 1970, and it was not until 32 years later in 2002 that Yuan Bingyu was able to see his father's tombstone.

Banding has advanced our understanding of bird migration and allowed us to witness the magnificence of bird life.

In 1956, ornithologist Chandler Robbins banded a black-backed albatross later named "Wisdom" at Midway Island. The albatross was wearing a flag numbered Z333. At that time, it was at least 5 years old. Since then, people have seen it at its birthplace almost every breeding season. It has continuously refreshed the record of the oldest wild bird known to breed, and has also been refreshing the record of the longest known bird banded.

Every year, whether it will return to Midway Island to breed concerns countless people. In 2020, Wisdom is at least 69 years old, and the flag on his feet has been changed 6 times. His age is much higher than the average lifespan of Laysan albatrosses. Scientists speculate that he has changed his mate several times. Even Robbins died three years ago, but he still came back and still showed us the miracle of life.

Technology upgrade, birds equipped with trackers

Although banding is simple and economical, it often depends on luck. The bird has to fly right in front of you for you to see it. Wouldn't it be better if you could also equip the bird with a small device to actively record its flight time and location while banding it? New technologies such as satellite tracking and geolocators have emerged.

With the development of artificial satellite technology, satellite tracking has also been used in the study of bird migration. Simply put, it is to let the bird carry a GPS tracker on its back, which can record the bird's location, transmit it to the ground via satellite, and then reach us after processing.

In 2007, ornithologists put a tracker on a bar-tailed godwit numbered E7. According to tracking data, it departed from New Zealand in the spring, flew to the mouth of the Yalu River in my country to rest, and then continued to fly to Alaska to breed. When migrating south in the fall, it flew for 8 consecutive days without eating or drinking, flying a distance of more than 11,000 kilometers, crossing the Pacific Ocean and returning directly to New Zealand, setting a new record for birds flying continuously without stopping. Some time ago, its partner flew for 11 days without sleep, and the distance increased by 10% to 12,200 kilometers, breaking this record.

Bar-tailed Godwit E7 wearing a satellite tracker (Image source: BBC News)

The flight path of Bar-tailed Godwit E7 (Image source: Global Flyway Network)

A photosensor is a device that records longitude and latitude based on sunrise and sunset times and daylight length. It cannot transmit data in real time and needs to be recaptured like a leg ring. However, compared with a satellite tracker, it is lighter and can be placed on small birds that cannot wear satellite trackers.

Arctic tern (Photo credit: AWeith under CC BY-SA 4.0)

Ornithologists have equipped 11 Arctic terns Sterna paradisaea with light-sensitive locators and found that these small birds, weighing only a little over 100 grams, can fly from the southernmost tip of the Earth to the northernmost tip of the Earth in 40 days, a distance of more than 40,000 kilometers. This trip across the poles is made twice a year. Most Arctic terns have a lifespan of 20 years, and the cumulative distance they fly is enough to travel from the Earth to the Moon and back twice.

The flight path of the Arctic tern (Image source: Egevang et al, 2010. )

Conclusion

Ornithologists have done everything possible to explore bird migration, returning to the original question: where is the destination of the birds' flight south?

In the video mentioned at the beginning, we can see finches and yellow finches, which are birds that can spend the winter in the north. In fact, they can be released where they are. Most migratory birds in the northern hemisphere do go to the south in winter, but the concept of "south" is relative, just as Hainanese people think that other provinces in China are in the north. Hedwig in "Harry Potter" - the snowy owl, usually lives in the Arctic and flies south in winter. Where do they fly south? Answer: Northeast China.

See the furry little paws? The snowy owl is wearing a down jacket. It will be too hot if it is sent to southern my country! (Photo credit: Bert de Tilly, CC BY-SA 3.0)

At present, these birds have been released in Dongting Lake. They may have a good life in Dongting Lake this winter, but no one knows what problems they will encounter when they migrate next spring. I hope these birds will migrate smoothly and continue to fly in the sky.

Author information: Wu Yang, PhD in Ecology, Beijing Normal University

Team introduction: Yunhai Science is an interesting science popularization team from Ocean University of China. They deconstruct seemingly profound scientific problems from the unique perspective of young people, allowing you to discover that nature is so interesting.

References:

[1] Wikipedia contributors. (2020, December 18). Pfeilstorch. In Wikipedia, The Free Encyclopedia. Retrieved 15:17, December 21, 2020, from https://en.wikipedia.org/w/index.php?title=Pfeilstorch&oldid=995037748

[2] Wikipedia contributors. (2020, December 5). Wisdom (albatross). In Wikipedia, The Free Encyclopedia. Retrieved 14:55, December 21, 2020, from https://en.wikipedia.org/w/index.php?title=Wisdom_(albatross)&oldid=992495889

[3] Gill, RE; Tibbitts, TL; Douglas, DC; Handel, CM; Mulcahy, DM; Gottschalck, JC; Warnock, N.; McCaffery, BJ; Battley, PF; Piersma, T. (2009). "Extreme endurance flights by landbirds crossing the Pacific Ocean: ecological corridor rather than barrier?". Proceedings of the Royal Society B. 276 (1656): 447–457. doi:10.1098/rspb.2008.1142.

[4] Egevang, C., Stenhouse, IJ, Phillips, RA, Petersen, A., Fox, JW, & Silk, JR (2010). Tracking of Arctic terns Sterna paradisaea reveals longest animal migration. Proceedings of the National Academy of Sciences, 107(5), 2078-2081.

[5] MA Zhijun. (2009). Research methods and progress in bird migration. Bulletin of Biology, 44(3), 5-9.