Swallows belong to passeriformes 1 genus. This genus of birds is small in size, with a body length of130 ~180 mm. The wing tip is long and the tail is forked. Most of the feathers on the back are blue-black, so they were called mysterious birds in ancient times. The wing tip is long and good at flying, the mouth is short and weak, and the mouth is wide, which is typical.

Mouth shapes of insect-eating birds. Short feet and strong claws. There are 20 species in the world and 4 species in China, among which domestic swallow and Jin Yan are more common. Swallows are chestnut red in the front waist, with irregular horizontal bands in the back chest and milky white in the abdomen. Swallows usually breed from April to July. Domestic swallows nest under the eaves of farmhouses. This kind of nest is made of saliva bonded with soil and grass stalks, and it is covered with fine and soft materials.

Grass, feathers, rags, etc. And some Artemisia annua leaves. The bird's nest is dish-shaped. Breeding 2 nests every year, mostly from May to early June and from mid-June to early July. Each nest lays 4 ~ 6 eggs. The second nest is less, 2 ~ 5 pieces. Eggs are milky white. Males and females hatch eggs together. 14- 15 days, chicks hatch and parents eat together. The chicks fly out in about 20 days, and then feed them for 5 ~ 6 days, so they can feed themselves. The food is full of insects. The golden waist swallow is similar in shape to the domestic swallow, but slightly larger. This swallow has a chestnut waist, which is very eye-catching, and a small black line in the lower body, which is easy to distinguish from domestic swallows. Habits are similar to those of domestic swallows, but most of them live in mountain villages. Yan is a typical migratory bird. After the breeding, the young birds still follow the adult activities, gradually integrate into the large group, and move south for the winter before the first cold wave comes.