Why does the insectivorous component of the tanager's diet increase significantly at a specific time during their annual cycle?

Answer

During nesting season when protein demands for rapidly growing young soar

The diet includes a high percentage of insects, particularly during nesting season, because the protein demands for feeding rapidly growing young soar at that time.

Why does the insectivorous component of the tanager's diet increase significantly at a specific time during their annual cycle?
birdfaunacharacteristicaviantanager