Why do swallows migrate in herringbone and word?

In order to save labor, the head swallow bears wind resistance when flying, which reduces the air resistance in the herringbone area behind it. Other swallows flying in the herringbone area will reduce physical exertion, so they can fly farther and farther. Generally, long-distance migratory birds will adopt this method, and they will take turns to be the first swallow to realize uninterrupted long-distance migration.

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.

They often feed during migration, so their fat reserves are lower than those of other migratory birds of the same size. Species that breed in Africa often migrate with rainfall patterns, but the specific situation is little known. Other species, such as the gray-waisted swallows, seem to wander around without a fixed migration route.

Extended data:

Almost all kinds of suborders only eat invertebrates in the air, mainly insects. Plant food only exists in a few kinds of food, and the intake is very small.

Only the two-color tree swallows regularly ingest plant substances (mainly berries), and this only happens during the insect shortage period. Yan is not an opportunistic forager. She won't fly around aimlessly and eat plankton in the air with her mouth open.

But take the initiative to prey on specific prey. Species distributed in the same field often prey on invertebrates of different sizes. As far as a certain kind of individual is concerned, it often chooses the biggest prey it can get.