Highest density of feathers

The bird with the highest density of feathers is the penguin. In his book The General Biology and Thermal Balance of Penguins (1967), Dr Bernard Stonehouse (UK) counted 11 to 12 feathers per cm2 in emperor, Adelie, yellow-eyed and fairy penguins. Each feather has its own small muscles associated with it to allow control. On land the feathers stay erect to trap air to insulate them, in the water they flatten to form a watertight barrier. Although emperor penguins have the longest feathers of all penguins, the types of penguins mentioned above share the record for densest – there is no info on which type of penguin has the densest. Penguins may have the thickest layer of fat for any bird, 2.3 cm (0.9 in) on an emperor.