Linked from
The 9 pages that link to Regurgitation, each with the reason it gives.
TrophallaxisRelated: Many ants deliver stored liquid food by regurgitating it to another insect.
Pigeon milkRelated: Adults transfer the secretion to chicks by feeding mouth to mouth.
AchalasiaRelated: Retained food and liquid can return from the poorly emptying esophagus.
Egyptian vultureRelated: Egyptian vultures may regurgitate food to feed their chicks.
Black-crowned night heronRelated: Adults feed nestlings by bringing up swallowed food.
SkuaRelated: A pursued bird may regurgitate its meal, which a skua can seize in flight.