Recently, a video on the Internet attracted everyone's attention: in front of a residential house in Wuchang City, Heilongjiang Province, dozens of swallows were scattered on the ground. The photographer of the video said that these swallows are no longer able to fly to the south to overwinter because the weather is too cold, and their fate may be coming to an end here. Coincidentally, a similar situation also occurred in Hunan.
Image source: Screenshot from social platform
Why are these swallows in such trouble? What kind are they? How can we help them?
Too long to read: During migration, swallows usually choose to migrate actively when the temperature is higher. When the temperature suddenly drops, the activity ability of swallows will decrease accordingly, and they will try to find a resting place with higher temperature.
The weather rhythm is disrupted, and low temperatures cause the flying height of insects to decrease, and swallows have to hunt at lower altitudes. Swallows that rely on flying insects cannot find food and are exhausted, so they become stranded or even die.
During extremely cold weather, swallows roost in clusters to stay warm, but if the weather continues to be severe, they may become unable to rejuvenate and remain dormant. The swallows in Heilongjiang were trapped this time because of the "cliff-like" temperature drop that prevented them from continuing their migration.
Why can't swallows migrate?
Swallows usually migrate in small groups of dozens of sizes when migrating. When these small groups gather during migration or at resting places (such as oasis in the desert, the coast before crossing the sea), they will form hundreds or even thousands of swallow flocks. Swallows usually prey on insects to supplement energy while migrating, so they prefer to fly at low altitudes during the day to feed. At the same time, swallows often gather food at resting places to reserve energy before crossing geographical barriers on their migration routes such as oceans and deserts.
Compared with low-temperature weather, swallow migration activities are usually more active when the temperature is higher. When the temperature drops, on the one hand, the activity ability of swallows decreases, and they will also seek resting places with higher temperatures; on the other hand, when the temperature drops, the flying height of insects will also decrease, forcing swallows to hunt at lower altitudes.
In cold weather, swallows will also roost in clusters to stay warm - they will line up in crowded rows, or even gather one on top of another in nests, tree holes and other places where they can avoid the wind and keep warm. In extremely bad weather conditions, swallows may no longer be able to resume their activities and sleep here, so people can sometimes find groups of frozen swallows in these places; this may also be the reason why early people (before the application of banding technology) thought that swallows overwintered in rock crevices or tree holes.
Researchers found many frozen barn swallows in a barn swallow nest in Zhanjiang | Photo by Tian Li
Low temperature weather will delay or interrupt the migration of swallows, forcing them to deviate from their normal migration routes, and even lead to migration failure. Especially for the young birds born in the same year, some of the young birds leave the nest late and will embark on a migration journey soon after leaving the nest. Completing the migration is a more severe challenge for these individuals.
What kind of swallows are these?
The swallow species we see in the video are mostly golden-rumped swallows (Cecropis daurica), with a small number of barn swallows (Hirundo rustica) mixed in.
Golden-waisted Yan丨Photographed by Wu Keying
From a taxonomic perspective, the “swallows” familiar to the Chinese people usually refer to members of the passerine order Passerineidae, of which there are 14 species in total. In the northeastern region of my country, golden-rumped swallows and barn swallows are common swallow species, and they are often distributed in the same tract, that is, both golden-rumped swallows and barn swallows are distributed in one area.
If you observe carefully, there are some differences in morphology between the two. The most obvious point is that the golden-rumped swallow has brown and maroon horizontal stripes on its waist, which is the origin of the "gold waist" in its name, while the barn swallow does not have this. In addition, the golden-rumped swallow has a body length of 16 to 20 cm, which is larger than the barn swallow (body length is about 13cm); the golden-rumped swallow has black vertical stripes on its lower body, while the barn swallow has no vertical stripes on its lower body.
Jiayan丨Photographed by Liu Yu
In spring and summer, two species, golden-rumped swallows and barn swallows, breed in northern my country. Their nests are often located under the eaves of residential buildings. The nest types of the two are also very different: the barn swallow's nest is an open bowl-shaped nest with the opening facing upward;
Jiayan’s “single-family apartment”丨Photo by Liu Yu
The nest of the golden-rumped swallow is a closed nest, usually with only one opening and shaped like a gourd.
Jinyaoyan’s “townhouse”丨Photo by Liu Yu
In Northeast my country and most other areas, golden-rumped swallows and barn swallows are summer migratory birds that come to breed in spring and leave for wintering grounds in autumn.
The wintering areas of golden-rumped swallows are mainly in Southeast Asia, and even extend to northern Australia. The wintering grounds of barn swallows in Northeast my country are also mainly in Southeast Asia: Between 2020 and 2022, researchers used photosensitive locators to study the migration of barn swallows in Northeast China (Panjin, Liaoning). The results showed that the autumn migration route of barn swallows is to the southwest, and most of their wintering grounds are in Thailand.
Facing the frozen swallows,
What can we do?
There are many things we can do to deal with frozen swallows. From a large perspective, climate warming is one of the important reasons for the frequent occurrence of such events. Each of us can practice green travel, avoid waste and other actions in our daily lives, and contribute to delaying climate warming.
If you encounter an injured or frozen swallow, you can contact your local wildlife rescue department for help. It is undeniable that rescue in similar situations is more difficult, requires higher levels of rescue personnel, and the success rate of rescue may also be very limited:
First of all, you must successfully capture the swallows without causing harm to them, and you must also protect yourself during this process;
Secondly, hypothermia may cause irreversible damage to birds, and most of the time we can only place hope on their tenacious vitality.
In addition, swallows feed on flying insects, so how to feed them is also a problem; weather and location suitable for release are also needed before the swallows can embark on their migration journey again.
But no matter what, for us, paying attention to and caring for wild animals and actively participating in biodiversity conservation is already a great act of kindness.
In addition, you can also participate in some swallow conservation projects. For example, the "National Swallows and Swifts Survey and Protection" project launched by the China Bird Watching Society in 2017 aims to pay attention to the survival status of swallows and protect their populations and ecological environment. (Everyone can participate in the national swallow nest survey by following relevant public accounts or video accounts, use the mini program to observe swallow nests, and contribute scientific data to the protection of swallows. You can also apply for artificial nest supports, etc., to help swallows survive better)
Potential impacts of relative climate and phenological changes on ecological mismatch in migratory birds. Migratory birds can only fully compensate for the effects of climate change if their arrival dates are significantly advanced (Saino et al. 2010).
As many netizens said in the video comments, the swallows in Heilongjiang are trapped in place because of the "cliff-like" temperature drop. They can only hope that the warmer weather will help them regain their vitality and start their migration journey again. The natural phenomenon of swallows being trapped due to sudden drops in temperature is not new, but it is undeniable that the frequency of such events may be increasing under the general trend of global climate change.
Birds that need to migrate are "risking their lives". The twice-yearly migration requires not only excellent technology, but also a lot of luck. Are the swallows that cannot move away just bad luck? I think this may be a wake-up call from nature to us.
References
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[2] Maclean, I. M. D., and R. J. Wilson (2011). Recent ecological responses to climate change support predictions of high extinction risk. Proceedings of the National Academy of Sciences 108:12337–12342.
[3] Malanoski, C. M., A. Farnsworth, D. J. Lunt, P. J. Valdes, and E. E. Saupe (2024). Climate change is an important predictor of extinction risk on macroevolutionary timescales. Science 383:1130–1134.
[4] Qin, P., Z. Xie, J. Zou, S. Liu, and S. Chen (2021). Future precipitation extremes in China under climate change and their physical quantification based on a regional climate model and CMIP5 model simulations. Advances in Atmospheric Sciences 38:460–479.
[5] Saino, N., R. Ambrosini, D. Rubolini, J. von Hardenberg, A. Provenzale, K. Hüppop, O. Hüppop, A. Lehikoinen, E. Lehikoinen, K. Rainio, M. Romano, and L. Sokolov (2010). Climate warming, ecological mismatch at arrival and population decline in migratory birds. Proceedings of the Royal Society B: Biological Sciences 278:835–842.
[6] Turner, A. (2006). The Barn Swallow. T & A D Poyser, London, UK.
[7] Turner, A., and G. M. Kirwan (2024). Eastern red-rumped swallow (cecropis daurica). In Birds of the World (S. M. Billerman, B. K. Keeney, P. G. Rodewald and T. S. Schulenberg, Editors). Cornell Lab of Ornithology.
[8] Ding Ping, Zhang Zhengwang, Liang Wei, and Li Xiangtao (2019). Chinese Forest Birds. Hunan Science and Technology Press.
[9] Zhang Fuyun and Yang Ruoli (1997). Research on bird migration in China. China Forestry Press.
[10] Tian Li, Zhou Caiquan, and Hu Jinchu (2006). Comparison of the reproductive ecology of Nanchong golden-rumped swallows and barn swallows and experiments on easy egg and chick production. Journal of Ecology 025:170–174.
[11] Zhao Zhengjie (1985). Birds of Changbai Mountain.
[12] Zheng Guangmei (2023). Catalog of Bird Classification and Distribution in China. Science Press, Beijing.
Planning and production
Author丨Liu Yu China Academy of Environmental Sciences
Review丨He Xin, researcher at Shanghai Museum of Natural History, PhD in Ecology from East China Normal University, director of Shanghai Science Writers Association
Planning | Fu Sijia
Editor丨Fu Sijia
Reviewer丨Xu Lai, Zhang Linlin