Determine which birds fly south first: insectivores or granivores. Why?

Birds fly south when they have nothing to eat.

Insectivorous birds fly away earlier. When the outside temperature drops, the insects gradually disappear, and the birds simply have nothing to eat.

Granivorous birds are much easier. In addition to the grain itself (wheat, etc.), which begins to ripen only closer to autumn, they can feed on various seeds, cones and seeds. Such food is easier to find: in addition to natural food sources (fields, plants, etc.), granivorous birds are often fed with various cereals, bread crumbs, etc., so they can remain for a long time.