Some birds swallow the food as they forage. When they return to the next, they regurgitate (vomit) it for the young.
Some birds, such as pigeons, produce a special liquid, called crop milk. This “milk” is part of the regurgitated food the baby birds receive.
The regurgitated food of petrels is mixed with an oil produced in the body of of the parent.
Raptors usually carry their prey back to the nest and tear it into bite-sized chunks for their chicks. This cuts down on all those trips to find more food.
The male and female cardinals in the video below are both collecting food to feed their hungry babies.