Why is it that duck and goose can forage even under water even without drowning or drinking too much?

Answer 1

They have a lamella. A lamella is a thin plate-like structure, often one amongst many lamellae very close to one another, with open space between. Aside from respiratory organs, they appear in other biological roles including filter feeding, the traction surfaces of geckos, and chloroplast membranes where high permeability is important.

Answer 2

Ducks and geese have adaptations that allow them to forage under water without drowning. They have specialized bills that filter out water and trap food, as well as a layer of oil on their feathers that repels water. Their bodies are also adapted to handle ingesting water while foraging by swallowing it and then expelling excess water.