How do crows live in human cities?

Let me tell you two short stories about crows.

1

Ten years ago, when I was in middle school, the school was a 20-minute bike ride away from home. In the winter morning, when I was riding my bicycle to school, I could see small groups of crows flying from the city to the outside of the city every day.

In the morning rush hour when everything is rushing towards the city, it is really strange to see such a wave of creatures moving outside the city. What's even more amazing is that when school is over, these crows fly back to the city from outside the city as if they have an appointment.

After seeing too many crows coming and going, I began to think about a very high-end question: Why do these crows wander around the city and outside the city every day?

2

There is a famous "Angel Road" near the south gate of Beijing Normal University. From dusk to early morning in winter, the trees on the roadside here will be full of crows, making it completely dark; the road under the trees will be covered with white flowers - those are angels (poop). Legend has it that if you haven't been hit by an "angel", you haven't been to Beijing Normal University.

In the past two or three years, the crows at Beijing Normal University have moved and dispersed. They are not concentrated on "Angel Road" as before, but the total number on the Beijing Normal University campus (and the Beijing University of Posts and Telecommunications next door) is still quite large. .

There are about 10,000 crows active at Beijing Normal University in winter, which is almost equal to the total number of undergraduate students at Beijing Normal University. So, besides Beijing Normal University, where else can you see a group of crows with such regular activity? What is the relationship between the activities of these crows and our lives and local environmental changes?

Today, we will explore the secrets of wintering crows in cities.

Crows in Sijiucheng

There are three types of birds with black feathers called crows in Beijing: large-billed crows, bald-nosed crows and small-billed crows. Among them, large-billed crows and bald-nosed crows are mainly found in the suburbs; while in Beijing, most of the crows that gather in large groups overnight are small-billed crows.

Small-billed crows are basically distributed throughout the country except in the hinterland of the Qinghai-Tibet Plateau, but they are more common north of the Yellow River. Some small-billed crows in the north are resident birds and do not migrate much. Some of them migrate south to East or even South China in winter. Among the large number of small-billed crows in Beijing in winter, there are some that breed in the northwest mountainous areas in summer, and some that migrate from the northeast to experience the winter in the imperial capital.

The Daily Life of a Crow

Around sunrise the next morning, these small-billed crows that stayed overnight in the city center would fly out of the city in twos and threes, and some of the lazy ones would fly out. It took more than an hour after sunrise to start moving. Where do they go when they leave the city during the day?

It is a garbage dump outside the city.

Crows are omnivorous birds - this is a more elegant way of saying it. The truth is, crows eat just about anything, and they especially like scavenging. Therefore, finding food from the organic waste in the garbage dump is one of the crows' favorite activities.

There are more than 20 million people in Beijing, and the amount of garbage produced by so many people is an astronomical figure. Most of this garbage is transported to several garbage disposal sites in the suburbs for landfill, and most of the landfill sites are open. For crows, this is a paradise with unlimited meals.

Why should we go out of heaven during the day?

For the small-billed crow, since so many garbage dumps in the suburbs are paradise, then why come to the city if you can eat and sleep in paradise? You know, you have to fly at least ten kilometers from the city center to the nearest garbage disposal site, and more garbage dumps are far away in places like Miyun, Changping. What’s the point of traveling dozens or even hundreds of kilometers to and from the city and outside the city in one day?

The crow in "Paradise". This photographer captured crows eating garbage in a very refreshing and otherworldly way.

Because - it's cold in heaven. In comparison, it is much warmer in the city. Everyone likes to sleep in a warm place, and crows are no exception.

Compared with suburbs, cities have higher density of buildings, traffic and population, and more efficient winter heating systems. This design makes the temperature in the city significantly higher than that in nearby suburbs, which is the legendary "urban heat island" phenomenon.

The closer to the center of a big city, the more obvious the urban heat island is, and the heat island phenomenon will be stronger at night. For example, in Beijing, the temperature in urban areas at night in winter can be about 3 times higher than in suburban areas.

This is the hourly fluctuation of the heat island intensity in urban Beijing in 2002. The vertical axis is the heat island intensity and the horizontal axis is the time, from 00:00 to 23:00. Obviously, the heat island effect is strongest after 18:00 in the evening and before 08:00 the next morning

For crows, another attraction of the city is the trees. A large number of tall trees are planted along urban highways, parks, and campuses, while most of the suburbs are dominated by farmland, and most of the trees have been cut down.

Crows like to sleep in groups in trees. More trees mean that more crows can rest, which allows the crows to detect danger in time (such as cats or weasels approaching the trees); it also fully satisfies the crows' desire to socialize in groups - they especially like it before going to bed. Make some noise.

Crows resting in clusters on dead trees can easily detect any approaching danger. Therefore, the large number of crows entering the city has no direct relationship with the so-called improvement of the ecological environment.

City of Crows

Not only in Beijing, but also in many places in North China and Northeast China, small-billed crows gather at night in winter. For example, some big cities in Tianjin, Hebei and Liaoning. Moreover, this kind of thing is not uncommon abroad. For example, the small-billed crow in Finland; and the short-billed crow in California, USA, both find cities to spend the winter.

In Tokyo, about 100,000 large-billed crows choose to stay in the city every winter. Local research has found that the number of crows entering the city has increased significantly in the past two decades, which is likely related to the increasingly abundant food sources.

In many big cities, there are stories about crows.

Too many crows will indeed cause some trouble. For example, friends who live near the crows’ night resting place will find it noisy; and a large number of crows means countless bird droppings. If there is a road under the tree, then The cleaning work will be very troublesome. If a car is parked on the roadside, it will be a complete tragedy. Too many crows gathering in the city center will also cause some potential health and epidemic prevention problems.

In addition, some crows bring the habit of digging through garbage into the city. Fortunately, in China, the trash cans are strong enough to withstand the abuse. But in places like Japan, every household will put their garbage bags at the door or at the garbage station, so crows often come to remove the garbage bags and then eat them (they are not responsible for cleaning up after eating). For example, the 100,000 large-billed crows in Tokyo are very keen on doing this kind of thing.

The scene of crows tearing apart garbage bags was very spectacular.

The Japanese solution is to reduce the use of plastic garbage bags and promote woven nets and metal fences so that crows cannot chew them. Of course, not all garbage stations in Japan have this facility, so crows can still find trash bags in the community that can be opened.

However, it is quite nice to see so many birds in the center of a big city - it would be terrible if a city was only densely packed with people and buildings and no other living creatures.