Why do you seldom see swallows in the north in recent years?

Swallows rarely appear in recent years, mainly for two reasons:

1, the suitable nesting sites are greatly reduced. Generally, swallows can be roughly divided into two categories, one is passeriformes, the more common ones are golden swallow and domestic swallows, the other is swift, and the more common ones are Louyan in the north and Little White Waist Swift in the south. White-waisted swift, domestic swallow and golden-waisted swift usually nest under the eaves. Nowadays, there are fewer and fewer traditional houses in the city, and many new buildings and buildings are not suitable for swallows to nest, because there is no eaves and glass curtain walls are widely used. Some buildings even poke the bird's nest down for the sake of beauty. Swifts usually nest in cracks in ancient buildings. But now, in order to protect ancient buildings, more and more buildings suitable for nesting are covered with bird-proof nets, which makes it more and more difficult to breed swift, resulting in a sharp decline in the number in recent years and is difficult to see.

2. Destroy human interests. Due to the sudden increase in the price of bird's nest in recent years, some people are greedy for money, looking for some buildings suitable for swallows to live in, destroying the nests of swallows, thus obtaining the sales of bird's nest, hindering the breeding process of swallows and reducing the number.