In some members of the Pelecaniformes, but most conspicuously in Pelecanidae (pelicans), the large, distensible pouch below the lower mandible of the bill that is used in catching fish. As it flies low over the water, the bird opens its bill and dips the lower mandible into the water. The mandible distends as it fills with water and fish. As the bird raises its head and closes its bill, the pouch contracts, forcing out water but retaining the fish.
Subjects: Zoology and Animal Sciences.