What is this? If you say: two Red-whiskered Bulbuls huddled together on a tree, then you must have very sharp eyes. They normally look more sleek and is one of the most common birds in Hong Kong. I have indeed seen them in many places around Hong Kong Island and Kowloon. These puffed up their feathers to look like fat hairballs because it is still quite cold, 14 degrees this morning, when I took the pictures in Shatin.
They are also called 高髻冠, for obvious reasons.