Feathers of birds are water proof due to secretion of?

Explanation

The correct answer is the preen gland. Birds use the preen oil secreted by the uropygial gland to waterproof their feathers. This oil helps maintain the integrity of the feathers and protects them from getting soaked, allowing birds to stay dry and maintain their ability to fly effectively. The other options, sudoriferous glands, endocrine glands, and thymus glands, do not play a role in waterproofing feathers.