This anniversary is celebrated twice a year!

Most anniversaries are celebrated only once a year, such as the annual World Animal Day on October 4. However, there is one global commemoration day that is very special. It is a "twice-a-year" festival, celebrated on the second Saturday of May and October each year.

October 8th is the second Saturday of October. Let us learn about this special commemorative day - World Migratory Bird Day .

Migratory birds are the "king of marathon"!

When it comes to migratory birds, many people's first reaction may be the wild geese that form a V-shaped or straight line in autumn, or the swallows that come here every spring. Indeed, it is possible to see birds migrating in autumn and spring. This is a journey that goes back and forth: in spring, birds leave their wintering grounds and head for their summer breeding grounds; in autumn, they return from their breeding grounds and fly to their wintering grounds; and then repeat this journey the next year.

Of all the birds, the Arctic tern (Sterna paradisaea) has the longest round-trip migration. They travel between the Earth’s poles, breeding in the Arctic summer and then flying to Antarctica to escape the cold winter in the Northern Hemisphere . In a study published in 2013, scientists tracked the round-trip migration of a population of Arctic terns and found that they migrated more than 90,000 kilometers a year, a little more than twice the circumference of the Earth! [1]

One and a half month old Arctic tern chicks (two on the right) are waiting to be fed by their parents. They have followed the flock from the Arctic to the Scottish town of Lerwick. Image source: Mike Pennington / geograph.org.uk

Migration ensures that birds have a stable food supply throughout the year and can avoid extreme weather conditions[2]. However, not every bird can successfully reach its migration destination. Bird migration can be imagined as a flying "marathon". Birds will overeat for more than two weeks before migration, storing energy in the form of fat in preparation for the upcoming "fat-burning" flight.

Newly born Arctic terns need to grow up quickly. One and a half months after birth, the young Arctic terns, who have just learned to hunt for food on their own, have to follow their parents to forage for food for several days, eat and drink enough to prepare for the migration "marathon" that will begin in half a month. However, when it comes to "overeating" before migration, the Ruby-throated Northern Hummingbird (Archilochus colubris) has a record of gaining nearly half its body weight in just four days before departure [3].

"Fat burning" flight, you need to

Supply Point

The fat stored before departure is actually consumed very quickly and is not enough to provide birds with all the energy they need for long-distance flights. Therefore, birds also need to be fed in a timely manner during migration. High-quality stopover habitats are crucial for successful migration[4]. Our urban green spaces and park wetlands are essential supply points for birds during migration.

For example, in October, it is easy to encounter wild ducks in the wetlands of North China. They may have just flown to the lake the night before and are resting and foraging on the lake during the day. The largest wetland reserve in the capital, Beijing Wild Duck Lake National Wetland Park , is named after the largest number of migrating geese and ducks . If the area of ​​such wetlands decreases or even disappears, migratory birds that need to rest in the wetlands will have nowhere to go, which may result in them being unable to complete the "marathon", seriously affecting the survival of the entire species.

Urban green spaces shelter migratory forest birds, such as small finches . However, these birds living close to human cities have encountered new challenges in recent years: glass windows and artificial lights at night in human cities have become the "death god" of many birds .

Who "killed" the migratory birds?

This is also a problem that has worried scientists in recent years. Researchers in the United States have found that in the United States alone, as many as 1 billion birds die each year from colliding with buildings, and most of these collisions occur on glass surfaces[5]. Glass windows have become the second largest cause of bird deaths.

Previous media reports have mainly emphasized the impact of glass itself on birds - glass windows are too "transparent" for birds to identify them as obstacles, so they fly into them. However, a study published in the journal Biological Conservation in 2020 pointed out that "light pollution" is also an important factor that needs to be considered independently, causing birds to fly into glass .

Through an investigation of bird collision accidents on 48 facades of 13 buildings in Minneapolis, Minnesota, scientists confirmed that the area of ​​artificial light shining through glass windows is the most important factor leading to collisions. The larger the illuminated area, the more likely it is that birds will collide with buildings; and this effect is unrelated to the size of the entire glass[5].

In addition to causing collisions, urban lights also affect the habitats that birds choose during migration[4], and even change the timing of when birds start migrating[6]. When it comes to migration, it is not the case that “the early bird catches the worm” and the earlier the better. If birds misjudge the timing of migration due to artificial light and arrive at their breeding grounds too early , they may arrive at a “marathon finish line” where food is not plentiful enough, the weather is not warm enough , and the environment is not ready to welcome them. After consuming a lot of energy, burning fat and even muscle, and finally reaching the “finish line”, migratory birds will basically starve to death if they cannot find food to replenish their energy within a few hours[3].

Purple martin (Progne subis) whose winter habitats have artificial light at night start their spring migration eight days earlier than their counterparts without artificial light, and arrive at their breeding grounds eight days earlier. This is not a good thing. Image source: Reference [6]

What many people may not realize is that the "geese flying south from north" we see during the day is just the tip of the iceberg of bird migration. Most bird migration actually occurs at night. This is why artificial light has such a big impact on bird migration, confusing or even killing migratory birds.

This year’s World Migratory Bird Day focused global attention on the threat of artificial light , and the campaign slogan was “ Turn off the lights, so migratory birds can return home safely ”[7]. In fact, we don’t even need to turn off the lights. We can contribute to the protection of migratory birds by simply closing the curtains and not letting the light through the windows affect the birds .

We admire the wonders of nature and celebrate the migratory birds twice a year. At the same time, every choice we make is also changing nature. For the safety of migrating birds, please draw your curtains at night .

References:

[1]Fijn RC, Hiemstra D, Phillips RA, et al. Arctic Terns Sterna paradisaea from the Netherlands migrate record distances across three oceans to Wilkes Land, East Antarctica[J]. Ardea, 2013, 101(1): 3-12.

[2]https://nationalzoo.si.edu/migratory-birds/introduction-migratory-birds

[3]http://www.shidicn.com/sf_4E11DA563B89438AA955997F47E6CD35_151_66FA58E1101.html

[4]McLaren JD, Buler JJ, Schreckengost T, et al. Artificial light at night confounds broad-scale habitat use by migrating birds[J]. Ecology Letters, 2018, 21(3): 356-364.

[5]Lao S, Robertson BA, Anderson AW, et al. The influence of artificial light at night and polarized light on bird-building collisions[J]. Biological Conservation, 2020, 241: 108358.

[6]Smith RA, Gagné M, Fraser K C. Pre-migration artificial light at night advances the spring migration timing of a trans-hemispheric migratory songbird[J]. Environmental Pollution, 2021, 269: 116136.

[7]https://www.cms.int/en/news/dim-lights-birds-night-%E2%80%93-world-migratory-bird-day-2022-slogan-announced

Author: hannah

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