What does a good mother duck use to distinguish between good and bad?

Judging from the appearance and body shape.

Distinguishing a good female water duck can be judged from the aspects of appearance, body shape and meat quality. The appearance requires the mother duck to have bright feathers, fat body and tender, crisp and fragrant meat.

Mother duck refers to wild ducks. It's a duck, but it's rich in nutrition and tastes much better than the ducks in captivity.