According to statistics, a swallow can eat 250,000 pests every quarter and 6,543.8+0,000 pests a year. Moreover, in ancient times, farmers found that once groups of swallows flew lower and lower, or groups of swallows slid quickly against the ground, or groups of swallows stood with their wings flapping, it would soon rain heavily.
This is because before the heavy rain comes, the air will become very humid and wet the wings of insects flying in the sky. Because of the airflow, the air pressure will be slightly lower before it rains, the air will become thinner and the oxygen content will be reduced, so insects will gather at low altitude. Swallows will hover at low altitude to prey on insects.
In addition, before the arrival of heavy rain, the airflow in the atmosphere was very chaotic, which made it difficult for swallows to get the correct wind, so it was difficult for them to spread their wings and fly very high, so they could only fly at low altitude.
In ancient times when the economy was dominated by small farmers, people found that the existence of swallows would help them reduce the number of insects and predict the weather through swallows, so they let swallows live under the eaves.
Swallows found that living under the eaves can not only better shelter from the wind and rain, but also resist natural enemies. The house where people live is suitable for building bird's nests, so swallows that don't nest under people's eaves have not been screened out.
But in recent years, the number of swallows has dropped sharply, all because swallows are facing a human-like problem? Housing difficulties.
With the development of China's economy, tile houses in rural areas are gradually renovated into bungalows. Swallows' nests are made of soil and grass stems bonded with saliva, which contain soft weeds, feathers, rags and some Artemisia annua leaves. Such nests are afraid of rain, and swallows will give up when they find water seepage after building their nests.
Therefore, it should be built at the corner of wide eaves and external walls, and the eaves with drooping structures in front guide running water, which is more attractive and prevents water from entering the nest.
The glass, tiles, terrazzo, plastic decorative boards and other surfaces of the bungalow are too smooth to be firmly bonded with the soil, and are no longer suitable for swallows to nest. Swallows can only nest in tree holes or cracks, or make holes in sand banks. In these places, there are often many natural enemies, so swallows can't resist the invasion of birds such as magpies and gray magpies and animals such as rats, cats, dogs and ferrets during their brooding period, and their living environment becomes worse.
Another point is that the rural population is getting smaller and smaller, and swallows will never nest in empty houses, because there will be more snakes and mice in empty houses, which will pose a threat to swallows. So swallows became a good symbol in ancient times. Who will nest in it? Prosperity? ,
Sparrows will also seize the nest of swallows. Swallows are migratory birds. They nest and breed under the eaves of the countryside every spring and summer, and migrate in autumn and winter. At this time, the swallow's nest may be occupied by sparrows, and sparrows are also active in places where humans live. They are extremely lively, bold and approachable, but they are very alert and curious.
Swallows can't compete with sparrows. Even if humans forcibly remove sparrows, the smell of sparrows will remain in the nest and swallows will not come again. In the end, it will only become the nest of other sparrows.
If this was good in the past, swallows could easily find other nesting places, but now swallows need to make greater efforts to find a nesting place.
Swallows don't build nests, so it's difficult to breed normally. Swallows generally breed in April-July, with 2 nests per year, mostly in early May-June and mid-June-early July. Each nest lays 4 ~ 6 eggs. The second nest is less, 2 ~ 5 pieces.
In addition, because of the popularity of pesticides, the number of insects in farmland is also decreasing. Without food source, young swallows can only starve to death, so the number of swallows is much less. In addition, insects will also be polluted by pesticides, and toxins will gather in the swallows who eat insects, which will directly lead to the decrease of swallows.
Swallows are still migratory animals. In winter, the food supply of swallows in temperate regions is greatly reduced, so many species migrate. But unlike most other passerine migratory birds, swallows migrate during the day and fly at low altitude. In addition, they often feed during migration, so their fat reserves are lower than those of other migratory birds of the same size. This makes it easier to encounter danger. According to the statistics of biologists, 80% of swallows die every year.
In recent years, due to the environment, human acquisition and other reasons, swallows continue to explore new living places in order to survive. For example, the distribution of red-fronted swallows has spread southward to Kenya and Tanzania, while the cave-cliff swallows have entered the southern United States from Mexico. And the change of environment will also cause the change of distribution mode. Ru Yan and other British people spent the winter in South Africa, and now their activities have expanded to the west, because the rainfall in the west has increased.
Although with the development of science and technology, humans no longer need swallows for insect control and weather forecasting, people should also pay attention to living in harmony with nature, and over-exploiting, transforming and destroying the natural environment will only pay for itself in the end.