Which order of birds has the most developed coccygeal gland?

The coccygeal gland received the greatest degree of development in birds of the order Anseriformes. This feature is associated with the habitat of these birds. Most of the time, the vast majority of these birds spend in various bodies of water. And the coccygeal gland secretes a secret with a very oily consistency. With the help of the beak, the birds apply the secretion of the gland to the feathers, this creates a protective layer that does not allow water to penetrate the feathers. Therefore, this property helps the birds to stay in the water for a long time and not get wet.