What? City life makes birds smart?

Imagine a hundred years ago in an European town, a milkman in braces placed two glass bottles of milk on the steps of a house on a bright morning, accompanied by birds. When he turned around, a group of prepared sparrows would biologically poke their heads into the bottle.

European blue tits and milk. Picture: Steve Magennis

In 1949, an article in British Birds about tits stealing milk fully exposed how humans were defeated by their bird rivals. The article is based on ornithologists Hinder and Fisher based on hundreds of surveys of British birdwatchers, milkmen, milkmen and others.

All birds can't digest milk, and neither can tits. There is a lack of lactose-breaking enzymes in birds. But the cream that floats on top of old milk contains little lactose, and these fats are important for birds that lack food in winter. In the late 19th and early 20th centuries, milkmen were used to leaving open milk bottles on their doorways in the early morning, when tits in Britain and Europe rushed their heads into the mouth of the bottle and ate a few centimeters of cream before other animals arrived.

In order to protect the milk, people launched several rounds of attack and defense with tits. In the beginning, people can only run to the door at the moment of the arrival of the milk delivery truck, and the tits who are not to be outdone will wait at the door on time to deliver milk every day. At some point in the 20th century, milk suppliers began to seal bottles with wax cardboard. It didn't stop for long, and in 1921, tits in Southampton, England, began to peck through and peel off the boards until the lid could be pierced by their sharp beaks. It wasn't long after replacing the aluminum cap, and by 1930, tits in 10 towns in England had learned to open metal bottle caps. To deal with metal lids, they first drill a small hole in the surface and then pull out the tin foil inside. The tit may pull the whole lid out and grab it with one claw and fly away until it is safe before pecking at the cream on the inside of the lid. If you can find the favorite tree of birds, you can clear a pile of covers under that tree.

Blue tits that have stolen a lot of cream. Picture: pinterest

Although there are tits that unfortunately drown in milk bottles while stealing food, human opponents are obviously at a disadvantage. In the Hinder and Fisher survey on tits' bottle-opening skills and human defenses, people complained indignantly about how fast the tits rushed to the bottle, usually within minutes of putting the milk on the steps-as if waiting. Maybe the birds are just waiting, and a milkman complains that some tits don't even wait for him to deliver the milk to the door, but attack his milktruck when he puts the milk bottle on the steps of the household! By the time he got back to the car, the birds would fly to the milk bottle that had just been delivered.) worst of all, a group of tits opened 57 of the school's 300 bottles of milk before the headmaster arrived. In some areas, milkmen are provided with heavy metal lids, stones or clothes to cover the delivered milk. But without exception, these tits have learned to remove obstacles.

In recent decades, tits seem to have finally been defeated by human rivals who drink milk. First of all, skim homogenized milk without cream layer is more popular. Over time, tits have learned to choose targets by distinguishing the colors of old-fashioned milk bottle caps. But after that, other materials replaced the aluminum lid glass bottle, the milkman also disappeared, and the supermarket was favored. Today, few people know the anger of milk stolen by birds.

Are the birds in the city smarter?

Urban tits without cream will not always go hungry in winter, and there is plenty of food in the city-the problem is that it is not easy to use these resources.

Arrogant to the city. Photo Source: ZeroOne/Flickr

Cities are the latest ecosystem on the planet, and tits have never encountered such an environment in the past thousands of years. In the natural ecosystem, resources are relatively scattered, individual density is not high, and predators are around all the time. A good strategy is to observe and wait patiently, and then show up after being sure that it is safe. In our view, we are shy, conservative and afraid of life. However, the city is rich in resources, a large population, and new things emerge in endlessly. Shyness means that the living space is squeezed, too conservative and underutilized. If you are afraid of life, you can't survive in the face of dense population, man-made machines and the noise and lights of modern society. Therefore, urban birds need to evolve more active survival strategies. They need to be bolder, more receptive to new things, and better able to take advantage of human neighbors who are inescapable and have a lot of resources.

We have seen the bold performance of European tits in the milk battle, and they are quite good at exploring resources and solving problems (removing paper caps, metal caps, bottle coverings). In fact, urban birds not only consider taking human property as their own, but also use human beings to solve old problems.

This is the case with the Japanese crow (Corvus corone) observed by Yoshiaki Ren, a scholar at Tohoku University in Japan in the 1990s. This kind of crow is a scavenger. It also eats fruits, seeds, insects and so on, especially walnuts. But Japanese walnuts are so small and hard that crows can't pry open their shells with their mouths. One way they use is to fly walnuts to an altitude of 10 meters and throw them back and forth until they break open the hard shell. The problem is that flying up and down is very tiring, and not every walnut can be broken. In 1992, Ren Ping Yiming observed an alternative way for crows to open walnuts in Sendai-putting them on the road and letting cars run them down. He recorded a total of 43 cases in 21 months. Most recorded crows put a walnut on the road where traffic is about to pass; more than 1/4 of crows choose an intersection with a signal so that they can accurately put the walnut under the wheel waiting for the light; he also observed that two crows placed walnuts on roads where cars were less likely to pass, which may be a failure imitation of their own kind. These behaviors appear in eight sections of Sendai. Renping Yiming believes that crows use cars to press walnuts through invention, learning, dissemination, and improvement, which is a systematic and intentional behavior.

The crow that is moving the walnut to the ideal position. Picture: Renping Yiming

City birds are bolder and better at solving problems.

Here is the question: are urban birds really smarter and more problem-solving, or do we lack a record of observing the clever practices of rural birds?

Tests of two groups of birds in the laboratory environment show that city birds may really be better at solving problems. A 2016 study of urban and rural red-bellied greyfinches (Loxigilla barbadensis) in Barbados by scholars at McGill University in Canada found that urban birds opened drawers faster than those from rural areas to eat in laboratory environments. In 2017, a study by the University of Arizona showed that Vermilion Bird, captured from urban and rural areas, performed similarly in undisturbed open-lid feeding tests, while urban birds had a slightly higher success rate, but when disturbed, the rural group was wiped out. These studies suggest that city life may have trained birds to solve problems and adapted them to human existence.

Neither the human wheel nor the human itself seems to be able to stop the resource expansion of urban birds. Even in 2016, Polish zoologists found that some urban birds are not only not afraid of strange human inventions, but even interested in new things. At 160 feeding sites in the city and surrounding countryside, they placed something that birds had never seen before-a bright green children's toy about the size of a lemon with a pinch of hair on top. The study found that in the absence of toys, the number of great tits in the city and in the countryside was similar; after putting the toys on the bird feeder, the number of birds coming to feed in the countryside was almost halved, while the number of great tits in the city was even more. The researchers believe that they may do so out of the need to be ready to take advantage of new resources.

Green toys look like this. Photo source: Tryjanowski et al.

There's a price to pay for being smart.

From this point of view, the increasingly pressing city birds are not going to turn against the sky. Almost every year, birds snatch sandwiches and ice cream from people's hands, leaving frightened passers-by. Since the city birds are so neat, they should live a very comfortable life in the city. But in fact, some comparative studies on the living conditions of urban and rural birds have come to the opposite conclusion-urban birds are under more pressure.

Indeed, urbanisation provides benefits such as food feeding, safe incubators and a warm winter environment for animals, including birds. But these animals are also subject to intraspecific and interspecific competition, as well as light, noise, diet and other pollution caused by humans, which has been shown to be associated with inflammation.

French scholars have studied the content of heavy metal zinc in Parisian pigeon feathers. Long-term exposure to heavy metals will damage the fertility of birds. In 2009, Marion Chatelain, a theoretical ecologist at the University of Paris VI, and his colleagues caught 97 pigeons from the streets of Paris and kept them in captivity for a year. After a year of feeding, the average zinc content in the feathers of the pigeons in the same part dropped to 1/3.

We may think that the continuous intake of heavy metals by urban pigeons is a single condition, and we are not sure how the urban environment affects birds as a whole. However, the results of a study on the exchange of urban and rural chicks at Lund University in Sweden almost made people cry.

In 2013, four researchers from the Department of Biology at Lund University conducted an exchange rearing experiment with Parus major chicks from urban and rural areas in southern Sweden. Fifteen days later, they took blood to measure the telomere length of the chicks' chromosomes. it was found that the chromosomal telomeres of birds growing up in cities (including half-nests born in cities and half-nests moved from the countryside) were more than 10% shorter than those of their brothers and sisters who grew up in the countryside. Telomeres are located at the ends of chromosomes, like plastic knots at the ends of shoelaces, maintaining the structural stability of genetic material. For humans, age and stress-especially in childhood-cause telomere depletion, which in turn affects gene function. For animals, telomere length is also associated with longevity. The experimental results show that the urban environment may accelerate the aging of the great tits and shorten the life expectancy, although the specific factors and mechanism are not very clear.

What did the environment do to birds: urban birds that grew up in the countryside (left) and country birds growing up in the city (right) in the Lund University experiment. Photo: P. Salm ó n

Even the biggest advantage of the city, more food, does not make the birds of the city live more calmly. Researchers at Virginia Tech found that although cities have more food, urban male songbirds (Melospiza melodia) are more aggressive than their rural counterparts, possibly because of cherishing and guarding territory and food, and they are not sure whether this is an offensive or defensive strategy.

Finally, it may be said that city life does make birds smarter, but smarter doesn't mean it's easier.

Compilation: vicko238

Original: Menno Schilthuizen

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