Cormorant, like most animals, are naturally buoyant which doesn’t help when you earn your living by diving for fish. What I didn’t know, until I looked it up, was that cormorants and their close relatives the darters decrease their buoyancy by having easily saturated plumage.
The microstructure of the feathers allows water to spread across the barbules, reducing the number and size of the air pockets between the water droplets and so increasing the amount of water within the structure of the feather.
The downside to this evolutionary strategy is the difficulty the birds have in shedding water after a dive. Which brings me to the contentious issue of why do cormorants stand for hours with their wings spread? Depending on which theory you subscribe to the behaviour is either to aid digestion after feeding, defend their territory or to dry out.
With so much now known about the hydrophobicity of their feathers and having personally watched the violent fully body shake immediately after leaving the water, I’m inclined to go with the drying out theory. They shed an enormous amount of water when they shake, but still look wet afterwards. I do wonder about the extended open beak behaviour. They don’t make a noise, just open up and almost gag; as if they have something stuck in the throat and are stretching the neck muscles and then contracting them to move it down.
As to issues with territory. I’ve not seen anything to suggest that they defend a particular area. There are at least a dozen birds on Cheddar Reservoir and they all use the bouys for drying.