'Regurgitated by the parent birds' means

Directions: Read the following passage and answer the question that follows:
Years ago, people woke up to find sparrows chirping in their backyard. A noisy lot, they took grains right from your hand if you had befriended them. They got over their fear easily and demanded food or water with their loud chirping if you had forgotten to give them their regular share of food. Tiny pink beaks opened to morsels of food or worms sometimes regurgitated by the parent birds. We had a splendid time watching the bird family bond and as children sat gazing at them as they picked up grain or splashed about us in muddy water.
Many people have written poems and lyrics on sparrows, their noisy chirps, their friendly nature, and their spotty feathers. Sparrows were a menace on the fields. There were guards with slings and stones to chase them away as they ate grains from standing crops. Now, people are trying to woo them back to nature.