Birds might not have sweat glands however they do lose water via respiration and in their droppings so most small birds might want to drink a minimum of twice a day. And, bathing is crucial for good feather maintenance. Birds dampen their feathers to loosen dust and help with preening. https://chancefghfe.bloguerosa.com/19600229/winterize-your-bird-baths-carlisle-pa-carlisle-pa