Tundra SwanSome of the advantages of flight:
1) Long distance movements (migration). Resident animals are limited by lower critical seasons. Migrants capitalize on seasonal abundances.
2) Short distance movements local access to food improved. Fruit, flowers, seeds are all patchily distributed, yet 27% of all birds are specialized to eat just these items. In fact, the flowering plants evolved at the same time as did birds, suggesting co-evolution.
3) New feeding modes opened. Flying insects now available (10% of birds specialize in eating flying insects). Flight also offers birds quick access to trees.
4) Escape from predators--(perhaps less important since flying predatory birds appear early on-geologically)