Hundreds of birds crashed to the ground at once! What happened?

Recently, in Chihuahua State in northern Mexico, an outdoor surveillance camera recorded a strange scene: a black flock of birds suddenly fell from mid-air and collectively crashed to the ground, instantly flooding the streets and houses, and then immediately flew away, leaving behind the corpses of birds on the streets.

Please tell me how much psychological trauma this video leaves on people | cbsnews.com

Subsequent reports by local media revealed the true identity of the bird. The blackbird in the video is a yellow-headed blackbird (Xanthocephalus xanthocephalus), which often gather in large groups and form mixed groups with other blackbirds. Every winter, flocks of yellow-headed blackbirds migrate from the United States and Canada to Mexico for the winter.

Flocks of Yellow-headed Blackbirds | Michael Andersen / flickr

The truth behind the impact

What happened to the birds outside of surveillance? At first, local veterinarians believed that they had inhaled toxic fumes or were electrocuted en masse by overloaded cables.

Ecologist Richard Broughton speculates that this is most likely caused by natural enemies (he claims to be 99% sure of this view). Predators may be chasing the birds from above, forcing them to the ground; at this time, the birds flying higher in the sky will also dive to the ground out of their instinctive escape reaction, forcing the lower birds in the flock to crash into buildings or the ground.

Raptors and starling flocks | solentnews.co.uk

The mass deaths of birds trying to escape their predators may seem bizarre and horrifying, but it actually happens from time to time.

In September 2018, a Vancouver resident witnessed a flock of birds falling from the sky after a raptor chased them. More than 40 birds died in the chaos.

In December 2019, 225 dead birds were found on a path on the island of Anglesey, Wales. Veterinarians performed autopsies on 41 of them and found that they had neither avian influenza nor toxic substances in their bodies, only trauma caused by impact. Therefore, it is more likely that they dived down and hit the ground while avoiding predators.

Bird carcasses are collected on Anglesey | bbc.com

Unlike the incident in Mexico, the protagonists of these two incidents are purple-winged starlings (Sturnus vulgaris), which are widely distributed on all continents and are the most likely flocking birds to be seen around us. Thousands of birds merge into one in the air, forming unpredictable geometric shapes, and if you witness this scene with your own eyes, you will be deeply shocked.

Spectacular bird waves | youtube

But in Rome, this shock has caused trouble for the citizens. The size of the starlings in Rome can reach millions, blocking out the sun and being very noisy. What's worse, they produce about 7 tons of feces. The bird droppings that fall like raindrops are all over the streets and alleys, whether it is cars, roads, or ancient buildings and sculptures.

Cars in Rome covered in bird droppings after bird storm | bbc.com

Why do we hold together?

Since flying in groups can cause serious "trampling accidents" when avoiding natural enemies, why do these birds still gather together? Currently, the academic community has proposed two possible reasons.

The first is to "huddle together for warmth," like penguins huddling together for warmth in an Antarctic snowstorm. When the cold night falls, the flock can also serve as a signal for more solitary birds in the wild to join in. After all, spending the night with so many companions is definitely much warmer than being alone.

Emperor penguin chicks huddle together for warmth | marcelalibertelli / inaturalist

But later, studies have shown that the size of the flock has nothing to do with temperature. The main reason they gather together is to defend against predators. Researchers believe that based on the dilution effect, the more birds there are in a flock, the lower the probability that each bird will become a meal for a bird of prey. Moreover, one more bird means one more pair of eyes, so the flock can more easily spot predators and react more quickly to escape.

In addition, the flock of birds constantly changes its shape in the air, which can also dazzle predators and make them wonder where to start. If you observe carefully, you will find that when facing the attack of predators, the changes of the flock of birds are like waves - the wave starts from the attack position of the predator and then spreads to the distance. Studies have confirmed that the formation of "waves" can indeed effectively reduce the success rate of predators.

When faced with a predator, a flock of birds suddenly becomes denser and changes shape | youtube

Flocks of birds constantly transform, split and reassemble, just like a single intelligent being. How do they achieve harmony and unity? In the 1930s, British writer and ornithologist Edmund Selous proposed a wonderful hypothesis: birds coordinate their movements through telepathy.

Now, people can use 3D photography to explore the secrets behind bird flocks. Andrea Cavagna, a physicist at the University of Rome, used this method to study the flocks of starlings over the city of Rome. In the end, he found that they had no leaders and no "collective intelligence". Instead, they followed a simple principle: when flying, each starling would refer to the 6 or 7 birds next to it to adjust its direction and speed. No matter how big the flock is, they will only follow the "pace" of their neighbors.

The researchers used different camera angles to photograph the flock of birds, matched the corresponding birds (red squares), and created a 3D model of the flock. | References [3]

Strange things happen from time to time

Not all cases of birds falling to the ground in large numbers are caused by being hunted by natural enemies.

On the afternoon of February 17, the campus of Radford University was as busy as usual, until dozens of lifeless robin (Turdus migratorius) fell from the sky. Students found more than 50 dead birds on the road and in the grass, as well as two survivors in a coma.

Biology professor Karen Powers speculated that the birds were actually drunk. The area had just experienced a sudden drop in temperature, and then warmed up again. The berries fermented in the cold and heat, forming alcohol. The birds ate too much fermented berries, but they were not good at drinking, so this tragedy happened.

Birds that eat berries are more likely to get drunk | Jean-Guy Dallaire / birdnote

Power lines can also be a "bird killer." Yes, birds standing on power lines can actually get electrocuted.

In early February, such an incident occurred. In Pembrokeshire, Wales, a woman was stopped by 200 dead starlings on the street while walking at night. Another witness provided a key clue-he heard a loud noise, similar to the explosion of lightning. Then several starlings fell from the sky and landed on his car.

Overcrowded flocks of birds caused short circuits in power lines | youtube

The worst mass die-off of birds occurred in September 2020. Hundreds of thousands of migratory birds in the southwestern United States could no longer reach the end of their migration and became cold corpses on the grass. When people found these birds, they had no excess fat reserves and very little muscle mass.

Some dead birds found by biologists at New Mexico State University. Most of them are long-distance migrants | theguardian

Normally, these migratory birds take off from the tundra of Alaska and Canada, pass through the southwestern United States, and finally reach their wintering grounds in Central America and South America. During the long journey, they need to rest every few days to replenish their energy before setting off again. The southwestern United States is one of the most important "gas stations" on this migration route.

Unfortunately, the western United States was experiencing a massive forest fire at the time, and these migratory birds had to take a detour through the Chihuahuan Desert, which was even more arid and barren, where water and insects were scarce.

Angeles National Park on the west coast of the United States, a fire is burning on the hillside | theguardian

In addition to the wildfires, the area also experienced a cold snap during that period, which brought extreme weather such as strong winds and snowfall, and a large number of insects were reduced. The extreme weather forced migratory birds to start migrating early, but they did not have enough food to replenish their energy and eventually starved to death on the way.

If you encounter injured wild animals, you should call the police, contact the local forestry department or wildlife rescue station as soon as possible. Even if you need to rescue them yourself, you must follow the guidance of the relevant departments. If you are at a loss when facing an animal in need of rescue, you might as well click on this article: Want to save animals? Here you will find all the answers you need. Helping injured animals requires love and scientific methods.

References

[1]Goodenough AE, Little N, Carpenter WS, Hart AG. Birds of a feather flock together: Insights into starling murmuration behavior revealed using citizen science. PLoS One. 2017 Jun 19;12(6):e0179277. doi: 10.1371/journal.pone.0179277. PMID: 28628640; PMCID: PMC5476259.

[2]Procaccini A, Orlandi A, Cavagna A, et al. Propagating waves in starling, Sturnus vulgaris, flocks under predation[J]. Animal behavior, 2011, 82(4): 759-765.

[3]Cavagna, A. and Giardina, I. (2008), The seventh starling. Significance, 5: 62-66. https://doi.org/10.1111/j.1740-9713.2008.00288.x

Author: Jian Er

Editor: Mai Mai

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