Swallows usually come and go in a few months.

Swallows usually come in March and leave in September.

Swallows began to migrate to the north in March, because it was beginning of spring in March, the temperature gradually increased, and food resources began to be rich. Swallows like to look for food in warm seasons and breed at this time. They choose to build nests in buildings, caves or trees to prepare their living environment for the next generation. The migration of swallows ends in September, which is the beginning of autumn. The temperature is gradually decreasing, and the food resources are decreasing. Swallows choose to leave the north and return to warm places for the winter.